Household secondary attack rate of COVID-19 and associated determinants.
COVID-19: Household secondary attack rate of COVID-19 and associated determinants. Spencer EA, Heneghan C.
Published on June 30, 2020
Transmission Dynamics of COVID-19
||Jing Q-L, Liu M-J, Yuan et al. Household secondary attack rate of COVID-19 and associated determinants. medRxiv 2020.04.11.20056010 2020
||U.S. National Institute of Health , the Science and Technology Plan Project of Guangzhou, the Project for Key Medicine Discipline Construction of Guangzhou Municipality, and the Key research and development program of China.
||Person to person, Close contact
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.
195 unrelated clusters with 212 primary cases, 137 nonprimary (hospital) cases and 1,938 uninfected close contacts were traced.
The household SAR was 13.8% (95%CI: 11.1 to 17.0%) if household contacts were defined as all close relatives and 19.3% (95%CI: 15.5 to 23.9%) if household contacts included only those at the same residential address as the case.
The odds of infection among children (<20 years old) was one quarter (OR 0.26, 95% CI: 0.13 to 0.54) of that among the elderly (≥60 years old).
There was no gender difference in the risk of infection. COVID-19 cases were at least as infectious during their incubation period as during their illness. On average, a COVID-19 case infected 0.48 (95% CI: 0.39 to 0.58) close contacts.
What did they do?
Using a comprehensive contact-tracing dataset from Guangzhou for 212 primary cases with 195 unrelated clusters, the population-level effective reproductive number and individual-level secondary attack rate (SAR) in the household setting were estimated.
The impact of age on transmissibility and the infectivity of COVID-19 cases during their incubation period were investigated.
- suspected COVID-19 case: a patient meeting ≥1 epidemiological criteria and ≥2 relevant clinical criteria
- confirmed case: a suspected case with positive detection of SARSCoV-2 nucleic acid by real-time RT-PCR or viral genes that are highly homologous to SARS-CoV-2 by sequencing using respiratory or blood specimens.
- asymptomatic: laboratory confirmation but without clinical signs, mainly found by outbreak investigation and contact tracing.
- close contact: an individual who had unprotected close contact (within 1 metre) with a confirmed case or an asymptomatic infection within 2 days before their symptom onset or sample collection.
Transmission estimates depend on assumptions of the duration of infectivity at different stages of infection and may introduce bias. The study did not reliably quantify the infectivity of asymptomatic infections given the limited number
|Clearly defined setting
||Demographic characteristics described
||Follow-up length was sufficient
||Transmission outcomes assessed
||Main biases are taken into consideration
What else should I consider?
The incubation period being more infectious than the illness period differs from the experiences with most respiratory pathogens.
About the authors