Transmission Dynamics of COVID-19

Analysis of the Transmission Dynamics of COVID-19: An Open Evidence Review.
Jefferson T, Spencer EA, Plüddemann A, Roberts N, Heneghan C.
https://www.cebm.net/evidence-synthesis/transmission-dynamics-of-covid-19/

In the midst of the COVID-19 pandemic, uncertainty on the characteristics of a novel disease reigns.  The explosive nature of COVID-19 transmission, initially shown by the number of new cases and later by admissions and deaths, remains unexplained.

One of the principal uncertainties regards the means by which COVID-19 is transmitted, with special regard to the factors which may accelerate or delay its spread, the mode of transmission, the role of asymptomatic infected people, its speed, the possible interactions with wildlife or livestock, urban or rural environments and population density.

The first part of this Open Evidence Review consists of searching the evidence and posting summaries of all included studies, which are accessible from the searchable table below. As we make more information available, we will define modes of transmission, publish updates with recommendations for policy, and set out a series of hypotheses to be tested by further work.


Published Updates:

4th September: Viral cultures for COVID-19 infectivity assessment. Systematic review  UPDATE Tom Jefferson, Elizabeth Spencer, Jon Brassey, Carl Heneghan

14th Sep: What does a case of COVID-19 really mean? Carl Heneghan, Tom Jefferson

7th Sep: Covid-19 and the end of clinical medicine as we know it  Carl Heneghan, Tom Jefferson

4th September: Viral cultures for COVID-19 infectivity assessment. Systematic review  UPDATE Tom Jefferson, Elizabeth Spencer, Jon Brassey, Carl Heneghan

1st Sep: Coronavirus cases are mounting but deaths remain stable. Why? Carl Heneghan, Tom Jefferson

21st Aug: It’s a mistake to think all positive Covid tests are the same Carl Heneghan, Tom Jefferson

21st Aug: Viral cultures for COVID-19 infectivity assessment. Systematic review  UPDATE Tom Jefferson, Elizabeth Spencer, Jon Brassey, Carl Heneghan

12th Aug: Could mass testing for Covid-19 do more harm than good? Carl Heneghan, Tom Jefferson

10th Aug: SARS-CoV-2 and the Role of Orofecal Transmission: Systematic Review. C HeneghanEA SpencerJ Brassey, T Jefferson.

5th Aug: Are you infectious if you have a positive PCR test result for COVID-19? T Jefferson, EA Spencer, J Brassey, C Heneghan.

4th Aug: Viral cultures for COVID-19 infectivity assessment Systematic review.T Jefferson, EA Spencer, J Brassey, C Heneghan.

16th July:  SARS-CoV-2 and the Role of Orofecal Transmission: Evidence Brief. Jefferson T, Spencer EA, Brassey J, Heneghan C.

10th July: Studying sewage could help solve a coronavirus mystery Carl Heneghan, Tom Jefferson. The Spectator.

3rd July: Environmental Weather Conditions and Influence on  SARS-CoV-2 Transmission.Spencer EA, Brassey J, Jefferson T, Heneghan C.

The Open Evidence approach

Our aim is to provide accessible summaries of the evidence of transmission dynamics for COVID-19. To achieve this we provide evidence  summaries that  include :

  • Bottom Line: the take-home points  
  • Evidence Summary: a summary of the main results
  • What did they do? the methods used
  • Study reliability: the points to consider when assessing whether the evidence is affected by bias
  • What else should I consider? Any further  points that add value to the research evidence

We will be undertaking systematic and regular searches for those studies that assess COVID-19 transmission, assessing the quality of the included studies and their implications. The review findings will be indexed on the Oxford Research Archive.

As we go we will set out policy recommendations. To interpret the study summaries we recommend not relying on single studies alone to draw conclusions. We will group the exposures into themes to provide a better understanding of transmission, highlight the key emerging messages, and build a useable, searchable database of the transmission variables for COVID-19.

If you are aware of any evidence that we should include, spot an error, or you just want to comment then email  cebm@phc.ox.ac.uk with the subject  line: transmission dynamics for COVID-19.

All the best the Open Evidence Review Team

Evidence explorer

There are 151 papers in this review

Filter papers by Transmission mode


























Title & bottom line Transmission
mode
Country
1 SARS-CoV-2 surface and air contamination in an acute healthcare setting in London

Despite apparent extensive air and surface contamination of  hospital environment, no infectious samples were grown.  A cutoff of RT-PCR of ct 30 or less is likely to be associated with infectious specimens.

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Aerosol, Droplets, Viral load UK
2 Virological characterization of COVID-19 patients that test re-positive for SARS-CoV-2 by RT-PCR

“Re-positive” cases are unlikely to be infectious as no intact RNA single helix was detected or live virus isolated. “Re-positive” discharged cases are caused by intermittent shedding of cells containing remnant RNA.

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Multiple, Viral load Guangdong, China
3 Detection and Isolation of SARS-CoV-2 in Serum, Urine, and Stool Specimens of COVID-19

No viral growth was detected in respiratory, urine, stool and blood samples despite a positive RT-PCR very soon after admission.

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Blood, Respiratory, Stool, Urine, Viral load South Korea
4 SARS-CoV-2 in Nasopharynx of Symptomatic Neonates, Children, and Adolescents

Half of the under 16s who were positive for SARS CoV-2 shed live viruses indicating the possibility of contagiousness. However, numbers were very small (out of 628 samples 23 were positive and 12 were live shedders.

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Respiratory, Viral load Switzerland
5 Cell-based culture of SARS-CoV-2 and safe de-isolation assessments during COVID-19

The threshold PCR Ct value for successful virus isolation was less than 32 for the N gene target. A Ct cut-off of ≥37 was not indicative of viable virus.

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Viral load Australia
6 Diagnostic accuracy of serological tests for covid-19: systematic review and meta-analysis

Higher quality studies of the accuracy of serological tests for Covid-19 are needed. Current evidence indicates that they are insufficiently accurate for use in point-of-care testing for Covid-19.

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Testing Any
7 Cell-based culture of SARS-CoV-2 and safe de-isolation assessments during COVID-19

The threshold PCR Ct value for successful virus isolation was less than 32 for the N gene target. A Ct cut-off of ≥37 was not indicative of viable virus.

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Viral load Australia
8 COVID-19 testing and correlation with infectious virus, cycle thresholds, and analytical sensitivity

Molecular detection of SARS-CoV-2 RNA did not mean infectious virus was present.   The use of Ct values and clinical symptoms in combination with PCR testing for SARS-CoV-2 provides a more accurate assessment of the potential for infectious virus shedding.

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Viral load USA
9 SARS-CoV-2 spillover into hospital outdoor environments

In six UK hospitals in April-May 2020 the point prevalence of SARS-CoV-2 carriage was 2.0% (23/1152 participants) and the median cycle threshold value 35.7 (IQR:32.4–37.6).

When prevalence of COVID-19 is very low, routine and repeated screening is unlikely to have significant value. This is underlined by the finding that the majority of healthcare workers testing positive by PCR in this study were unlikely to be infectious.

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Asymptomatic, Viral load UK
10 Contact Tracing during COVID-19 outbreak, South Korea

During lockdown in South Korea, positive PCR-test cases of COVID-19 were identified among 12% of household contacts and 1.9% of non-household contacts.

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S Korea
11 SARS-CoV-2 virus culture and subgenomic RNA from patients with mild Coronavirus disease

In respiratory specimens of COVID-19 patients mainly with mild disease culturable SARS-CoV-2 and subgenomic RNA (good indicator of replication) was rarely detectable beyond 8 days after onset of illness although virus RNA by RT-PCR remained for up to 70 days.

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Respiratory, Viral load China, SAR Hong Kong
12 Duration of infectiousness and correlation with RT-PCR cycle threshold values in cases of COVID-19 in England.

RT-PCR cycle threshold (Ct) values correlate strongly with cultivable virus and likelihood of infectiousness.

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Droplets, Viral load UK
13 Viable SARS-CoV-2 in the air of a hospital room with COVID-19

Patients with respiratory manifestations of COVID-19 produce aerosols in the absence of  aerosol-generating procedures that may contain viable SARS-CoV-2.

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Aerosol USA
14 Clinical Course and Viral Shedding Among Patients With SARS-CoV-2

Many SARS-CoV-2 infected people remained asymptomatic for a prolonged period, and viral load was similar to that in symptomatic patients. Isolation of infected persons should be performed regardless of symptoms.

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Droplets, Viral load Korea
15 COVID-19: Clinical Utility of Cycle Threshold Values

Lower Cycle threshold values may be associated with worse course of illness and outcomes and threshold values may be useful in predicting the clinical course and prognosis of patients.

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Mixed, Viral load Global
16 Shedding of infectious virus in hospitalized patients with COVID-19

Patients with severe or critical COVID-19 may shed infectious virus for longer periods of time compared to what has been reported for in patients with mild COVID-19. Quantitative viral RNA load assays and serological assays should be used for test-based strategies to discontinue or de-escalate infection prevention and control precautions.

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Viral load Netherlands
17 COVID-19: Prolonged virus shedding even after seroconversion

A 50 year old woman continued to shed live virus until day 18 and non viable virus until day 63 from symptom onset.

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Droplets Taiwan (traveller from Wuhan)
18 Impact pathogenicity of SARS-CoV-2

Viable viral isolates were extracted from sputum (n=7), stool samples (n=3) and  one nasopharyngeal sample  indicating that the SARS-CoV-2 is capable of replicating in stool samples

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Droplets, Orofecal China
19 SARS-CoV-2 RNA at different time points

SARS-CoV-2 RNA was positive in stools, nasopharyngeal and oropharyngeal swabs at different time points.

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Mixed, Orofecal Italy
20 Viral RNA load as determined by cell culture for SARS-CoV-2 patients

There was a significant relationship between Cycle Threshold (Ct) value and culture positivity rate: samples with Ct values of 13–17 all had positive culture. Culture positivity rate decreased progressively according to Ct values to reach 12% at a Ct of 33.

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Droplets France
21 Persistence of intestinal SARS-CoV-2 infection in stool samples

Intestine SARS-CoV-2 infection affects the disease course of COVID-19 and the digestive system is the main target organ of SARS-CoV-2 in some patients.

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Orofecal China
22 Viable SARS-CoV-2 in saliva, urine, and stool from COVID-19 patients

There was viable SARS-CoV-2 in saliva, urine, and stool from COVID-19 patients up until days 11 to 15 of the clinical course suggesting that viable SARS-CoV-2 can be secreted in various clinical samples as well as respiratory specimens.

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Droplets, Mixed, Orofecal Korea
23 Culture-Based Virus Isolation and Potential Infectivity of Clinical Specimens for COVID-19

Cycle threshold may be a predictor of culturability but the small sample size of this study needs developing to propose an acceptable threshold or ways to calibrate PCR to achieve a high PPV on culturability and hence infectiousness. Viral genome integrity isolation is also an important pointer to infectivity

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Droplets Taiwan
24 Prolonged presence of SARS‐CoV‐2 in pediatric patients

Three children showed a prolonged presence of SARS‐CoV‐2 in feces after throat swabs were negative.

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Orofecal China
25 Detection of SARs-CoV-2 in Stool Specimen from an asymptomatic Child

An asymptomatic child was positive for a coronavirus by reverse transcription PCR in a stool specimen 17 days after the last virus exposure.

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Orofecal China
26 SARs-CoV-2 was detected in the throat and rectum of a patient in Vietnam.

In a single case report, SARs-CoV-2 was detected in the throat and rectum of the  patient with COVID‐19.

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Mixed, Orofecal Vietnam
27 Viral load of SARS‐CoV‐2 in stool samples

Stool samples from 9/17 confirmed patients (53%) were positive on RT-PCR analysis.

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Mixed, Orofecal China
28 SARS‐CoV‐2 in 10 patients with COVID‐19 in Macau.

SARS-CoV-2 can be shed in the stool and the assessment of both fecal and respiratory specimen is recommended

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Droplets, Orofecal Macau, China
29 Five cases of COVID-19 in France

SARs-CoV-2 viral RNA was detected in the stools of two women out of the case series of five patients

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Orofecal France
30 The first case of COVID-19 in the USA

Stool obtained in a single case report was positive for SARs-CO-V-2 on day 7 of the illness.

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Orofecal USA
31 Characteristics of the first 12 patients with COVID-19 in the United States

SARS-CoV-2 RNA was detected in at least one nasopharyngeal (NP) swab, 11/12 oropharyngeal (OP) swab and 7/10 in the stool. 

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Droplets, Orofecal USA
32 Detectable SARS-CoV-2 in blood and anal swab

SARs-CoV-2 RNA was readily detected in the blood (6/57 patients) and anal swabs (11/28 patients).

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Mixed, Orofecal China
33 Prolonged SARS-CoV-2 shedding in the respiratory tract and feces of children

Prolonged virus shedding is observed in the respiratory tract and feces of children at the convalescent stage.

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Droplets, Orofecal China
34 Clinical course of 18 patients infected with SARS-CoV-2 in Singapore.

SARS-CoV-2 Virus was detectable in the stool of 4 of 8 hospitalized patients.

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Orofecal Singapore
35 SARS-CoV-2 in urine, blood, anal swabs and oropharyngeal swabs samples

Virus was found in urine, blood, anal swabs (n =2) and oropharyngeal swabs of nine patients diagnosed with COVID-19

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Mixed, Orofecal China
36 Persistence and clearance of SARS-CoV-2

Clearance of viral RNA in patients’ stools was delayed compared to oropharyngeal swabs.

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Orofecal China
37 SARS-CoV-2 productively infects human gut enterocytes

SARS-CoV-2 infects enterocyte lineage cells in a human intestinal organoid model.

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Orofecal Netherlands
38 Predicting infectious SARS-CoV-2 from diagnostic samples

SARS-CoV-2 Vero cell infectivity of respiratory samples from SARS-CoV-2 positive individuals was only observed for RT-PCR Ct < 24 and symptom onset to test of < 8 days. 

Infectivity of patients with Ct >24 and duration of symptoms >8 days may be low.

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Community Canada
39 Aerosol and Surface Transmission Potential of SARS-CoV-2

All samples taken were COVID 19 cases in isolation facilities were contaminated, indicating that SARS-CoV-2 may spread through both direct (droplet and person-to-person) as well as indirect mechanisms (contaminated objects and airborne transmission). The concentration of contamination was independent of patients’ symptoms and coughing. The findings support the use of airborne isolation precautions when caring for COVID-19 patients.

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Close contact, Droplets, Fomites, Person to person USA
40 Virological assessment of hospitalized patients with COVID-19

Nine cases of COVID-19 that provide proof of active virus replication in tissues of the upper respiratory tract.

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Droplets, Orofecal Germany
41 Direct evidence of active SARS-CoV-2 replication in the intestine

SARS-CoV-2 was detected in the rectum of a COVID-19 patient during the incubation period. There was direct evidence of replication of SARS-CoV-2 in the intestine.

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Orofecal China
42 Aerosol and surface distribution of SARs-CoV-2 in hospital wards, Wuhan, China

In a hospital treating COVID-19 patients, SARS-CoV-2 RNA was found widely distributed in surface and air samples.

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Aerosol, Fomites China
43 Environmental contamination of SARS-CoV-2 in healthcare premises

Widespread contamination of commonly used surfaces including personal protective equipment  imply the absolute requirements for routine cleaning and disinfection of surfaces.

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Fomites China
44 The presence of SARS‐CoV‐2 RNA in the feces of COVID‐19 patients

Sixty seven percent (28/42) laboratory-confirmed hospitalised COVID-19 patients tested positive for SARS-CoV-2 RNA in stool specimens; this was not associated with the presence of GI symptoms or severity of illness. Among them, 18 (64%) patients remained positive for viral RNA in the feces after the pharyngeal swabs turned negative, for a duration of 6 to 10 days.

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Orofecal China
45 A familial cluster of pneumonia associated with COVID- 2019 indicating person-to-person transmission

This very early study established the likelihood of person to person transmission of SARS-CoV-2, in hospital and family settings. It also highlighted the possibility of transmission from asymptomatic carriers.

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Asymptomatic, Close contact, Orofecal, Person to person China
46 Transmissibility of coronavirus between symptomatic and asymptomatic patients: reanalysis of the Ningbo COVID-19 data

This reanalysis of data from Ningbo, China, showed no difference in the transmission rates of coronavirus between symptomatic and asymptomatic cases.

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Close contact, Community, Person to person China
47 Transmission and clinical characteristics of COVID-2019 in 104 outside-Wuhan patients, China

Following implementation of control measures in Hunan Province, household transmission accounted for most cases, suggesting effectiveness of lockdown measures. Transmission from asymptomatic relatives was observed (two cases).

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Close contact, Person to person China
48 Detection of SARS-CoV-2 in an independent and assisted living community for older adults in Seattle, Washington

Symptom-based screening might not identify SARS-CoV-2 infections in independent and assisted living facility residents.

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Close contact, Person to person USA
49 Contamination by SARS-CoV-2 from a symptomatic patient

Severity of symptoms is no guide to intensity of viral shedding but all post cleaning samples were negative and current decontamination measures appeared sufficient.

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Close contact, Droplets, Fomites, Orofecal Singapore
50 COVID-19: Hygiene monitoring during the Coronavirus Disease 2019 outbreak in a Chinese hospital.

SARS-Cov-2 RNA were positive from inlets of the sewage disinfection pool and negative from the outlet of the last sewage disinfection pool but no viable virus was detected by culture. Strict disinfection and hand hygiene could decrease the hospital-associated COVID-19 infection risk of the staffs in isolation wards.

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Fomites, Orofecal China
51 COVID-19: Transmission within a family cluster by presymptomatic carriers in China

Within a family cluster of eight  cases among nine family members, clinical manifestations varied from asymptomatic to severe pneumonia, and timing of symptom onset varied.

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Presymptomatic China
52 The role of asymptomatic SARS-CoV-2 infections: systematic review

Evidence from early in the pandemic suggests that most SARS-CoV-2 infections are not asymptomatic throughout the course of infection, and that transmission by presymptomatic accounts for around 40-60% of transmission and asymptomatic cases accounts for around 15% of transmission.

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Asymptomatic, Presymptomatic Global
53 Temporal dynamics in viral shedding and transmissibility of COVID-19

Among 77 transmission pairs, highest viral load in throat swabs was observed at the time of symptom onset and declined thereafter; therefore infectiousness may peak prior to symptom detection.

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Presymptomatic China
54 SARS-CoV-2 clusters in the UK, France, and Spain

This preliminary report shows that 21 people were established to be associated with a COVID-19 case in a ski resort in France that led to 12  subsequent infections in France, UK and Spain.

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Close contact, Person to person UK, France, Spain
55 Transmission risk of SARS-CoV-2 to healthcare workers in a primary care hospital setting

This study of exposure to an index case in a primary care hospital found a low risk of SARS-CoV-2 transmission. It suggests that routine short clinical examinations and short physical contacts did not facilitate transmission.

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Close contact, Person to person Switzerland
56 Investigation of a COVID-19 outbreak in Germany resulting from a single travel-associated case

Cases in this study in Bavaria, Germany presented with predominately mild, non-specific symptoms. Infectiousness before or on the day of symptom onset was substantial. The incubation period was often short and false-negative tests occurred.

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Close contact, Person to person Germany
57 SARS-CoV-2 transmission in different settings: Analysis of cases and close contacts from the Tablighi cluster in Brunei Darussalam

For 71 cases observed in Brunei, factors associated with higher onward transmission among 1,755 close contacts were attendance at local religious gatherings and household contact. Workplace and social setting transmission was low.

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Close contact, Person to person Brunei
58 Household Transmission of SARS-CoV-2, Zhuhai, China, 2020

This prospective study of 148 household contacts found a secondary infection rate of 32% within households.

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Close contact, Person to person China
59 2019 novel coronavirus family clustering in Zhejiang Province

Within family clusters, the number of secondary cases was two to three times higher among spouses than children, parents or other family members.

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Close contact, Person to person China
60 COVID-19: Theories on the proximal origin of SARS-CoV-2.

Three possible origin theories are proposed and discussed. Not enough data are available to accept or reject any of the hypotheses.

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Mixed N/A
61 Gastrointestinal features in COVID-19 and the possibility of faecal transmission.

Gastrointestinal symptoms are common in COVID-19 patients and were observed with increased prevalence as the epidemic progressed in China. SARS-CoV-2 enters GI epithelial cells, and the faeces of COVID-19 patients are potentially infectious.

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Orofecal Mostly China
62 Concentration and detection of SARS coronavirus in sewage in China

No live SARS-CoV was found in any sewage samples from two hospitals receiving COVID-19 patients. SARS-CoV RNA was detected in sewage concentrates of two hospitals receiving SARS patients prior to disinfection, and occasionally after disinfection.

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Orofecal, Waterborne China
63 Sentinel surveillance of SARS-CoV-2 in wastewater anticipates the occurrence of COVID-19 cases.

SARS-CoV-2 was detected in sewage 41 days before the declaration of the first COVID-19 case in Spain and in frozen samples dating back to 12 March 2019. If confirmed, the results suggest SARS CoV-2 has been around longer than first thought.

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Orofecal, Waterborne Spain
64 COVID-19: Differential occupational risks to healthcare workers from SARS-CoV-2

Among 9,809 healthcare employees in a UK hospital in the south-east, an increased risk of COVID-19 was found in staff in acute medicine, among Black and Asian staff, and porters and cleaners. Protective interventions including PPE appeared to reduce risk among intensive care staff.

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Close contact, Person to person UK
65 COVID-19: TMPRSS2 and TMPRSS4 promote SARS-CoV-2 infection of human small intestinal enterocytes.

In a laboratory study, human enterocytes expressing high ACE2 receptor levels could support infection with SARS-CoV-2. However, the virus is rapidly inactivated in the GI tract, and no infectious virus was obtained from stool samples from COVID-19 patients.

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Orofecal USA
66 Digestive symptoms in COVID-19 patients with mild disease

Among a group of hospitalised patients with low severity COVID-19, digestive symptoms were present in 57%. Patients with digestive symptoms were more likely to be fecal virus-positive than those with respiratory symptoms.

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Orofecal China
67 COVID-19: Molecular and serological investigation of 2019-nCoV infected patients

This study indicated that RNA of SARS-CoV-2 maybe shed via multiple bodily routes, and highlights that COVID-19 is found in anal swabs sometimes when oral swabs show no viral RNA.

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Orofecal China
68 Prevalence of gastrointestinal symptoms and fecal viral shedding in patients with COVID-2019: a systematic review and meta-analysis.

This review reports that the Gastrointestinal tract supports the growth of SARS-CoV-2 to an extent similar to previous SARS infections and that gastric symptoms are frequently experienced in COVID-19.

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Orofecal N/A
69 COVID-19: Is SARS-CoV-2 Also an enteric pathogen with potential fecal-oral transmission?

Various observational and mechanistic evidence supports that SARS-CoV-2 can infect and be shed from the human gastrointestinal tract.

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Orofecal N/A
70 COVID-19: Infection of bat and human intestinal organoids by SARS-CoV-2.

SARS-CoV-2 can infect bat intestinal cells, and demonstrated SARS-CoV-2 replication in human intestinal organoids, suggesting that the human intestinal tract might be a transmission route of SARS-CoV-2.

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Orofecal N/A
71 SARS-CoV-2 in serum, urine, and stool specimens of COVID-19 patients from the Republic of Korea.

SARS-CoV-2 RNA was detected in serum, urine or stool samples in 20% of patients hospitalised with COVID-19. However, the virus could not be isolated from these samples and therefore the risk of transmission via these media is not established. 

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Orofecal, Urine South Korea
72 Infectious SARS-CoV-2 in feces of patient with severe COVID-19.

This case series of 28 hospitalised patients for whom faeces samples were available indicated that infectious virus was present in faeces from two cases who also tested positive for viral RNA by RT-PCR.

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Orofecal China
73 COVID-19: Household transmission of SARS-CoV-2 in Wuhan.

The observed rate of secondary transmission among household contacts of hospitalised patients with SARS-CoV-2 infection was 30%.

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Close contact, Person to person China
74 A cluster epidemic of COVID-19 in a supermarket in Liaocheng, Shandong Province.

Several cases were apparently transmitted from a supermarket worker.

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Close contact, Person to person China
75 Asymptomatic and paucisymptomatic SARS-CoV-2 infections

This study of two cases and six subsequent infections amongst close family contacts suggests SARS-CoV-2 transmission through asymptomatic or paucisymptomatic infections is possible.

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Close contact, Person to person China
76 COVID-19: Toilets dominate environmental detection of SARS-CoV-2 in a hospital

Of 107 surface samples (37 from toilets, 34 from other surfaces in isolation rooms and 36 from other surfaces outside isolation rooms). Four samples were positive (2 two ward door door-handles, one bathroom toilet toilet-seat cover and one bathroom door door-handle). Three were weakly positive from a bathroom toilet seat, one bathroom washbasin tap lever and one bathroom ceiling exhaust louvre. One of the 46 corridor air samples was weakly positive.

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Orofecal China, Nanjing
77 The characteristics of household transmission of COVID-19

The secondary attack rate of SARS-CoV-2 within households was 16%. Increased age and being the spouse of the index case increased risk of transmission. Isolation within the home of the index patients, at the onset of symptoms, prevented household transmission.

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Close contact, Person to person China
78 Risk of transmission in COVID-19 among close contacts

2.6% of close contacts of cases contracted COVID-19; almost half were asymptomatic or had  mild infection. The main transmission appeared to take place via household contacts.

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Close contact, Person to person China
79 SARS-CoV-2 infection from contaminated water systems

Based on data from 39 countries, SARS-CoV-2 can remain stable within water for up to 25 Days. Country-specific risk of infection posed by faecal contaminated water is environment-dependent, with water flow and temperature as important variables.

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Orofecal, Waterborne 32 Countries
80 COVID-19: Preparation for Quarantine on the Diamond Princess Cruise Ship

Infection rate was high and clinical harm was considerable onboard the cruise ship. A number of operational difficulties hampered ideal isolation and quarantine procedures onboard.

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Close contact, Fomites, Person to person Japan
81 COVID-19: High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice – Skagit County, Washington, March 2020

This study of choir practice attendees suggests that transmission of COVID-19 was facilitated by close proximity and physical contact and may have been augmented by the act of singing.

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Aerosol, Close contact, Fomites, Person to person USA
82 COVID-19: Cluster of Covid-19 cases in the French Alps, 2020

This study highlights the variation possible in transmission between close contacts and also that cases’ clinical experience is highly variable including asymptomatic.

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Close contact, Person to person, Superspreading France, England and Spain
83 COVID-19: Community Transmission of SARS-CoV-2 at Two Family Gatherings in Chicago

Gatherings likely to involve physical greetings and prolonged close proximity probably increase transmission of SARS-CoV-2.

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Close contact, Person to person USA
84 COVID-19: Potential for Foodborne transmission of COVID-19

Extensive uncertainty on the ecology of SARS-CoV-2 makes it hard to make specific recommendations on handling and prevention of transmission. CoV are susceptible to heat, surfactants and low PH.

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Orofecal Global - New Zealand
85 COVID-19: High temperature and high humidity reduce the transmission of COVID-19.

Some of the variations in COVID-19 transmission between cities worldwide can be explained by higher temperature and humidity being associated with lower transmission rates.

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Meteorological, Urban environment China and USA
86 COVID-19: Temperature significantly changes COVID-19 transmission in 429 cities

Lower weather temperatures were associated with higher COVID-19 transmission. There might be a most conducive temperature for the viral transmission, which may partly explain why it first broke out in Wuhan at that time.

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Meteorological China
87 SARS-CoV-2 in Paris wastewaters

Quantitative monitoring of SARS-CoV-2 genomes in wastewaters may enhance surveillance intelligence of circulation at local or regional scales.

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Orofecal France
88 SARS-Coronavirus-2 in sewage in the Netherlands

SARS-CoV-2 was detected in the sewage of five sites a week after the first COVID-19 case in the Netherlands. Even at low COVID-19 prevalence sewage surveillance could be a sensitive tool to monitor the viral circulation.

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Orofecal, Waterborne Netherlands
89 SARS-CoV-2 Infection in Fecal Samples from Hong Kong

Fecal discharge continues long after respiratory shedding of COVID-19 has ceased.

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Orofecal Hong Kong
90 COVID-19: Fecal-Oral Transmission of SARS-CoV-2 In Children

In children, the orofecal route is an alternative route of transmission, regardless of presenting COVID 19 symptomatology. Exclusion of SARS-CoV-2 infection by single time point nasopharyngeal swabs should not be used in children.

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Orofecal Italy
91 Investigating SARS-CoV-2 surface and air contamination in a London hospital

Many hospital surfaces and air samples contained viral RNA. Viable virus was not cultured from any sample.

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Aerosol, Fomites UK
92 COVID-19: Evidence for gastrointestinal infection by SARS-CoV-2

SARS-CoV-2 may both infect the gastrointestinal system and transmit via a faecal-oral route. 

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Orofecal China
93 Prolonged presence of SARS‐CoV‐2 viral RNA in faecal samples

In 98 hospitalized COVID-19 cases, patients’ faecal samples remained positive for SARS-CoV-2 for a mean of 11 days (maximum 5 weeks) after respiratory tract samples became negative.

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Orofecal China
94 Fecal specimen diagnosis of novel coronavirus‐infected pneumonia

A small pilot sample of 14 cases  indicated agreement for the presence of COVID-19 between oropharyngeal sample and fecal samples.

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Orofecal China
95 First detection of SARS-COV-2 In untreated wastewaters in Italy.

SARS-CoV-2 RNA fragments have been identified in sewage in Italy however the WHO protocol for sewage treatment of enveloped viruses after appropriate modifications is viable. The authors report a novel RT PCR test for screening of waters.

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Orofecal, Waterborne Italy
96 COVID-19: Persistent viral shedding of SARS-CoV-2 in faeces

There is a high rate of PCR positive persistence of SARS-CoV-2 in faecal samples of patients with COVID-19.

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Orofecal Global (Mainly China)
97 COVID-19 in wastewater

Recreational water could have concentration of SARS-CoV-2 agent via faulty wastewater management

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Orofecal Global
98 COVID-19: Children with negative nasal specimens excrete SARS‐CoV‐2 in stools

Three children with mild symptoms who were SARS‐CoV‐2 throat swab specimen negative on discharge from hospital were stool positive 10 days post-discharge

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Orofecal China
99 COVID-19: Viral loads in throat and anal swabs in children infected with SARS-CoV-2

In some children, fecal shedding may be a sign of prolonged mildly asymptomatic infection and represent the final phase of the disease.

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Orofecal China, Wuhan
100 COVID-19: fecal shedding in children

Fecal shedding in children with COVID-19 occurs on average nine days longer than by the respiratory route

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Orofecal Brazil/Global
101 COVID-19: Coronaviruses in water environments

Coroviridae have been isolated in different types of liquids from waste to surface water but in general, they appear to be unstable. Chlorination and higher temperatures lead to their inactivation.

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Orofecal, Waterborne Global
102 Epidemiological Characteristics of COVID-19 Close Contacts in Ningbo City

Transmission rates varied by closeness of contact and by type of contact. A single case travelling on a bus and attending a mass gathering appeared to be responsible for infecting 25 individuals

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Close contact, Community, Superspreading China
103 Household secondary attack rate of COVID-19 and associated determinants.

COVID-19 cases in their presymptomatic period were at least as infectious as during their symptomatic period, and household contacts and elderly people were the most susceptible to infection.

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Close contact, Person to person China
104 Epidemiology and transmission of COVID-19 in Shenzhen, China

Case isolation and contact tracing reduces the time during which cases are infectious in the community.

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Close contact China
105 Hospital transmission of COVID-19 in a general ward in Hong Kong

None of 120 contacts of a patient with initially undetected COVID-19 subsequently became infectious, suggesting SARS-CoV-2 is not spread by an airborne route. 

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Aerosol, Close contact, Droplets Hong Kong, China
106 COVID-19 Outbreak in a Call Center, South Korea.

High attack rates were identified for workers in an office space.  A map of the workspace and cases demonstrates the likelihood of close working contact increasing risk.

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Close contact, Person to person South Korea
107 Isolation of SARS-CoV-2 in untreated wastewater in Australia

SARS-CoV-2 was deleted for the first time in Australia using RT-qPCR assay, confirmed by sequencing

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Orofecal Australia
108 Asymptomatic COVID-19 cases on board the Diamond Princess cruise ship

18% of cases were estimated to be asymptomatic on board the Diamond Princess cruise ship 

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Close contact, Person to person Japan
109 COVID-19: Estimates suggest COVID-19 transmission rates are highly seasonal

Seasonal temperature is associated with COVID-19 transmission globally, with 1°C increase in local temperature associated with 13% fewer cases.

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Meteorological Global
110 The spread of SARs-CoV-2

Rapid spread may have been facilitated by significant numbers travelling outside of Hubei before lockdown.

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Person to person China, Wuhan provinces other than Hubei
111 Potential faecal transmission of SARS-CoV-2

SARs-CoV-2 may be transmitted oro-fecally, but the number of studies in the present study with findings of viable virions in the faeces is small making this mode of transmission uncertain.

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Orofecal China, Singapore, USA
112 COVID-19: Effects of temperature and humidity on the daily cases and deaths

Temperature and relative humidity were negatively correlated with daily new cases and daily new deaths of COVID-19.

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Person to person 166 countries (excluding China)
113 Factors influencing the sharp increase in COVID-19 in Northern Italy.

Administrative organisation issues, human bias, and bureaucracy in relevance to the epidemic are key factors in the extreme outbreak in Northern Italy.

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Meteorological, Pollution Italy
114 High transmissibility of COVID-19 near symptom onset.

The transmission was highest around the time of symptom onset and reduced quickly over subsequent days. Secondary infection was higher among household contacts than that in healthcare or other settings.

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Person to person Taiwan, China
115 Transmission of COVID-19 to Health Care Personnel

Unprotected, prolonged patient contact, as well as certain exposures, including some aerosol-generating procedures, were associated with SARS-CoV-2 infection. 

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Nosocomial, Person to person California, USA
116 Transmission path of COVID-19 cluster cases in Zhuhai, China

Transmission in Zhuhai appears to be occurring mainly within close groups such as families.

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Person to person China
117 Travel-Related Cases of SARS-CoV-2 in America.

No transmission among non-household contacts was detected. Among 15 household contacts, only 2 secondary cases (each the spouse of the respective case) were detected.

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Close contact, Fomites, Person to person USA
118 SARS-CoV-2 infection in health care workers

Among 12 Health care workers diagnosed with COVID-19 asked to recall their working patterns pre-outbreak, poor sleep quality and high working pressure were positively associated with higher risks of COVID-19 diagnosis.

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Fomites, Person to person China
119 Transmission dynamics of children with COVID-19 in China

Children were more likely to have asymptomatic infections, milder conditions, faster recovery, and better prognosis than adults

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Person to person China
120 Presymptomatic Transmission of SARS-CoV-2 in Singapore

Investigation of 243 cases of COVID-19 in Singapore identified seven clusters in which presymptomatic transmission was the most likely explanation for secondary infections.

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Presymptomatic Singapore
121 Transmission of the novel coronavirus onboard the Diamond Princess

Passengers and crew in the cruise ship experienced high transmission rates, hypothesised to be due to the close quarters and confined living spaces.

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Close contact, Person to person Japan
122 Close contact and risk of SARs-CoV-2 infection

In transmission events, after sharing a meal or staying at a chalet the secondary attack rate is estimated as very high.

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Close contact, Person to person China and France
123 COVID-19: Transmission Dynamics in Taiwan

Most transmission of COVID-19 occurred at the early stage or even before symptom onset, as symptoms developed and progressed the secondary attack rate decreased

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Person to person Taiwan
124 A systematic review of SARS-CoV-2 transmission

The mean household SAR was 15% (95% CI: 12% to 19%) – ranging from 6.6% in Taiwan to more than 30% in four Chinese cities. Secondary attack rate from symptomatic index cases contact was greater than asymptomatics

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Close contact, Person to person Various
125 Atmospheric circulation and the spread of COVID-19 in Europe

Strong atmospheric stability with dry conditions favoured viral spread by short-range droplet transmission.

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Droplets, Meteorological Italy, Spain
126 Absolute humidity and transmission of COVID-19

Changes in weather alone will not necessarily lead to declines in COVID-19 case counts without the implementation of extensive public health interventions.

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Meteorological SE Asia
127 COVID-19: Temperature, humidity and latitude analysis to predict potential spread and seasonality

The transmission of COVID-19 is associated with the 30 to 50 degree N’ longitude corridor and weather patterns and low specific and absolute humidity.

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Meteorological Global
128 Effect of Temperature, humidity, and wind speed on COVID-19

Calm, cold, dry and overcast conditions are favourable to the transmission of COVID-19.

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Meteorological 310 regions from 116 countries by 12 March 2020
129 COVID-19: Transmission aboard the Diamond Princess cruise ship

Swift action by diagnosis, testing, contact-tracing and isolation would have probably avoided the majority of 619 cases aboard. 

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Close contact, Fomites, Person to person International waters and Yokohama, Japan
130 COVID-19: Transmission amongst cruise ship passengers

Eighty-one percent of COVID 19 patients on a cruise ship were asymptomatic. Prevalence on affected cruise ships is likely to be underestimated and monitoring after disembarkation is necessary.

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Close contact, Fomites, Person to person South Atlantic
131 COVID-19: Mechanisms for Accelerated Diffusion in Italy

The accelerated and vast diffusion of COVID-19 in Northern Italy was associated with the duration of cities’ exposure to polluted air.

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Pollution Italy
132 Suppression of the COVID-19 outbreak in the municipality of Vò, Italy

In one of the two original epicentres of the outbreak in Northern Italy, Vò Euganeo, cases were  infected in the community before lockdown, or subsequently from asymptomatic infected people living in the same household.

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Person to person Italy
133 Hospital outbreak of COVID-19 in South Africa

Separate access and segregation of potentially infected patients are required to prevent or control nosocomial outbreaks of COVID-19.

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Fomites, Person to person South Africa
134 COVID-19: Early transmission dynamics in Wuhan, China, of novel coronavirus-infected pneumonia

COVID-19 transmission was occurring since mid-December 2019 in Wuhan: the majority in the Huanan Seafood Wholesale Market. A lack of early testing may have missed cases, particularly those with atypical symptoms.

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Person to person China
135 Seasonal coronaviruses and establishing the context for COVID-19 emergence

Seasonal coronaviruses were detected in 4% of patients with respiratory illness who were tested at primary/secondary healthcare settings.

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Seasonality Scotland, UK
136 SARS-CoV-2 Survival in Relation to Temperature and Humidity and Potential for Seasonality

Evidence suggests reduced transmission in high ambient temperatures and humidity, but it is limited and inconsistent.

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Meteorological Worldwide
137 COVID-19: Early transmission dynamics in Nigeria.

The transmission was slow in the early weeks of the pandemic in Nigeria compared with other countries, which may be related to differences in case ascertainment.

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Community, Imported Nigeria
138 COVID-19: Climate and early global patterns of the outbreak

Temperature and humidity are strongly associated with the variation of the growth rate of Covid-19 cases across the globe in the early phase of the outbreak.

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Meteorological 189 countries/regions
139 COVID-19: weather, demographics and infection timeline.

In a multivariable model only population density and the timeline remained statistically significant.

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Meteorological Worldwide
140 Association of Temperature and Humidity with Transmission of COVID-19 in China

Increases in temperature and humidity were associated with lower levels of  COVID-19.

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Meteorological China
141 COVID-19: Associations of climate and public health interventions

Transmission of COVID-19 was associated with weakly associated with relative or absolute humidity and not associated with latitude and temperature.

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Meteorological 144 geopolitical areas worldwide
142 COVID-19: Presymptomatic Transmission in a Skilled Nursing Facility

On the basis of the reconstruction of an outbreak of COVID-19 in a skilled nursing facility, the presence of symptoms is not a sufficient indicator of infection. Viral shedding can continue for at least a week after testing positive.

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Person to person USA
143 Infectivity of Asymptomatic SARS-CoV-2 Carriers

None of the 455 contacts of a single case of asymptomatic SARs-CoV 2 turned positive after a month.

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Close contact, Droplets Guangdong province, China
144 Transmission of COVID-19 in South Korea.

The transmission of SARS-CoV-2 in South  Korea was exacerbated by super spreading events in confined settings, including a hospital, a church and a gym.

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Person to person, Superspreading South Korea
145 Settings linked to SARS-CoV-2 transmission clusters

The results found evidence of SARS-CoV-2 transmission clusters for 152 events, which was classified into 18 types of settings.

For the references see the online database.

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Close contact, Person to person Worldwide (results mostly from Asia)
146 Fecal dissemination of SARS-CoV-2 virus genome in COVID-19 patients in India

This pilot study in India found SARS-CoV-2 RNA in fecal samples from 12 symptomatic and asymptomatic COVID-19 patients.

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Orofecal India
147 Isolation of SARs-CoV-2 from stool specimen of a confirmed case of COVID-19.

Live virus has been isolated from the stools of one severe pneumonia case, pointing to a possible oro-fecal spread.

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Orofecal China
148 Detection of SARS-CoV-2 in Different Types of Clinical Specimens

In this case series from China, two stool specimens out of 44 positives contained live virus, suggesting that orofecal transmission is possible. Transmission of the virus by respiratory and extra respiratory routes may help explain the rapid spread of disease.

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Close contact, Droplets, Orofecal, Person to person China
149 SARS-CoV-2-positive sputum and feces samples in COVID-19 patients

This retrospective study of 133 hospitalised COVID-19 patients identified 22 whose sputum or fecal samples tested positive after their pharyngeal swabs became negative.

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Orofecal China
150 Characteristics of pediatric SARS-CoV-2 infection and persistent fecal viral shedding.

This study of ten children with COVID-19 found that symptoms among children were nonspecific and relatively mild; rectal swabs tested positive among 8/10 cases even once nasopharyngeal tests became negative.

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Orofecal China
151 Aerosol Transmission of COVID-19

Transmission of COVID-19 may take place by fine droplets emitted by infected people with no symptoms when they speak or breathe without necessarily coughing or sneezing.

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Aerosol, Droplets UK

Policy recommendations

Investigate the transmission dynamics of COVID-19 in hospitals, nursing homes and dormitories, using classic investigative methods of testing, interview and graphics to reconstruct an outbreak. Read the full recommendation

COVID-19 Dashboards should aid the understanding of outbreak clusters, highlight super spreading events and facilitate mitigation strategies. Read the full recommendation

Funding

This work is supported by the National Institute of Health Research Evidence Synthesis Working group, and by Maria and David Willetts.