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:

5th August: Are you infectious if you have a positive PCR test result for COVID-19? Tom Jefferson, Elizabeth Spencer, Jon Brassey, Carl Heneghan  www.cebm.net/covid-19/infectious-positive-pcr-test-covid-19/

4th August: Viral cultures for COVID-19 infectivity assessment. Systematic review.          Tom Jefferson, Elizabeth Spencer, Jon Brassey, Carl Heneghan. medRxiv 2020.08.04.20167932; 

16th July:  SARS-CoV-2 and the Role of Orofecal Transmission: Evidence Brief. Jefferson T, Spencer EA, Brassey J, Heneghan C. www.cebm.net/covid-19/sars-cov-2-orofecal-transmission/

10th July: Studying sewage could help solve a coronavirus mystery. Carl Heneghan, Tom Jefferson. The Spectator. www.spectator.co.uk/article/studying-sewage-could-help-solve-a-coronavirus-mystery

3rd July: Environmental Weather Conditions and Influence on Transmission of SARS-CoV-2 . Spencer EA, Brassey J, Jefferson T, Heneghan C. www.cebm.net/covid-19/weather-conditions-sars-cov-2/

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 134 papers in this review

Filter papers by Transmission mode




















Title & bottom lineTransmission
mode
Country
1 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
2 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
3 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
4 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
5 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
6 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
7 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
8 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
9 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
10 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
11 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
12 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
13 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
14 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
15 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
16 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
17 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
18 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
19 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
20 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
21 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
22 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
23 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
24 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
25 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
26 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
27 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
28 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 transmission Close contact Orofecal Person to person  China
29 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
30 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
31 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
32 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
33 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
34 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 transmission  China
35 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 transmission Presymptomatic transmission  Global
36 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 transmission  China
37 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
38 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
39 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
40 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
41 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
42 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
43 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
44 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
45 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
46 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
47 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
48 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
49 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
50 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
51 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
52 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
53 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
54 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
55 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
56 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
57 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
58 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
59 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
60 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
61 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
62 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
63 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
64 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
65 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
66 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
67 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
68 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
69 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
70 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
71 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
72 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
73 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
74 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
75 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
76 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
77 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
78 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
79 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)
80 COVID-19 in wastewater

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

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Orofecal  Global
81 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
82 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
83 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
84 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
85 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
86 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
87 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
88 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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Close contact Droplets  Hong Kong, China
89 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
90 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
91 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
92 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
93 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
94 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
95 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)
96 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
97 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
98 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
99 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
100 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
101 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
102 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
103 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 transmission  Singapore
104 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
105 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
106 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, China
107 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
108 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
109 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
110 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
111 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
112 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
113 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
114 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
115 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
116 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
117 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
118 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
119 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
120 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
121 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
122 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
123 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
124 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
125 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
126 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
127 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
128 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)
129 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
130 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
131 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
132 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
133 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
134 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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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.