Study population and setting
Researchers in Guangzhou, China used contact tracing data reported to the Guangzhou Municipal Centers for Disease Control reported between January 7 and February 18, 2020. This included 349 confirmed COVID-19 cases that formed 195 clusters of 215 index cases and 134 secondary or tertiary cases. The sample also included 1,964 uninfected contacts from these cases.
Summary of Main Findings
The attack rate for household contacts from index cases was 12.4% when defined based on close relatives versus 17.1% when household contacts were defined based on residential address. The household attack rate was lower among contacts <20 years of age (OR: 0.23, 95% CI: 0.11, 0.46) and contacts aged 20-59 years (OR: 0.64, 95% CI: 0.43, 0.97) compared to those 60 years or older. Overall, the secondary attack rates were not statistically different the incubation period and symptomatic period though the attack rate was non-statistically significantly lower during the symptomatic period (OR: 0.61 [95% CI: 0.27,1.38]). The estimated effective R (average number of individuals infected by a case given the proportion of Guangzhou that were susceptible) was 0.5 (95% CI: 0.49, 0.74).
The study provides further evidence of the occurance of early transmission prior to symptom onset.
Although the researchers included asymptomatic cases in the analysis, there were only a few of these individuals and a proxy date for symptom onset was used, which may not be a valid comparison to symptomatic cases.
This was one of the first studies to utilize contact tracing data to estimate infectivity during the incubation period and contributes knowledge concerning basic epidemiologic features of coronavirus (e.g. effective reproductive number) in the context of social distancing and masking wearing.
This review was posted on: 1 August 2020