Bi (2020)
Epidemiology and transmission of COVID-19 in 391 cases and 1286 of their close contacts in Shenzhen, China: a retrospective cohort study
Patient characteristics
Contact history (Sharing household vs. Non sharing household)
SARS COV-2 infection
Odds ratio: 6.270 (1.490-26.330) Adjusted model


Retrospective cohort study

Medical records


391 SARS-CoV-2 cases and 1286 close contacts in Shenzhen, China

The mean age of the population was 45 years, and 307 (79%) of 391 cases were adults aged 30–69 years. At the time of first clinical assessment, most cases were mild (102 [26%] of 391) or moderate (254 [65%] of 391), and only 35 (9%) were severe. 330 (84%) of 391 cases had fever at the time of initial assessment, while 25 (6%) of 391 had no signs or symptoms. As of Feb 22, 2020, final clinical outcomes were known for 228 of 391 cases, with three who had died (all captured through symptom-based surveillance) and 225 who had recovered.


12 Day

SARS COV-2 infection


Suspected cases and close contacts were tested for SARS-CoV-2 by RT-PCR of nasal swabs. SARS-CoV-2 transmission by estimating key values, such as the household secondary attack rate, serial interval, and observed reproductive number (R).

Patient characteristics

Contact history

Household contacts and those travelling with a case were at higher risk of infection

Non sharing household

Sharing household

Odds ratio

6.270 (1.490-26.330)




Contact type - household, travel, meal

Infected and uninfected close contacts provide key insights into the epidemiology of SARS-CoV-2. Isolation and contact tracing reduce the time during which cases are infectious in the community, thereby reducing the reproductive number.