HealthDay News – Severe acute respiratory syndrome coronavirus 2 has high transmissibility within households, according to a study published online June 17 in The Lancet Infectious Diseases.

Qin-Long Jing, PhD, from the Guangzhou Center for Disease Control and Prevention in China, and colleagues estimated the secondary attack rate of COVID-19, defined as the probability that an infected individual will transmit the disease to susceptible individuals among household and nonhousehold contacts. One hundred ninety-five unrelated close contact groups (215 primary cases, 134 secondary or tertiary cases, and 1964 uninfected close contacts) were traced between January 7 and February 18, 2020.

The researchers found that the estimated secondary attack rate among household contacts was 12.4% when household contacts were defined as close relatives and 17.1% when household contacts were defined on the basis of their residential address, assuming a mean incubation period of 5 days, a maximum infectious period of 13 days, and no case isolation. The risk for household infection was lower in the youngest age group (<20 years) and for those aged 20 to 59 years compared with the oldest age group (≥ 60 years; odds ratios, 0.23 [95% confidence interval, 0.11 to 0.46] and 0.64 [95% confidence interval, 0.43 to 0.97], respectively). Greater infectivity was suggested during the incubation period than the symptomatic period, although the differences were not statistically significant (odds ratio, 0.61; 95% confidence interval, 0.27 to 1.38).

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“The infectiousness of patients with COVID-19 during their incubation periods is high and could substantially increase the difficulty of curbing the ongoing pandemic,” the authors write.

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