Where the world is gradually (or instantaneously) facing the COVID-19 reality, China claims victory. Yet, it ain’t over till it’s over, and many fear a rebound once daily life has returned to its normal practices and contact patterns. In the meantime our Chinese colleagues keep on producing very impressive epidemiological studies. Such as this one, published today.
They describe data collected by the Shenzhen CDC on 391 cases of COVID-19 (detected between Jan 14 and Feb 12) and 1,286 of their close contacts. This is outside of Hubei province.
They performed “symptom-based surveillance”, which included “symptomatic screening at airport and train stations, community fever monitoring, home observation of recent travellers to Hubei, and testing of hospital patients.” With this approach they identified 77% of the 379 patients in whom the mode of detection was known.
What they did with to control this virus: “Symptomatic cases were isolated and treated at designated hospitals regardless of test results. Asymptomatic positives were isolated at centralized facilities. Close contacts and travelers from Hubei testing negative were isolated at home or a central facility, and monitored for 14 days. PCR testing was required for all close contacts at the beginning of isolation, and release was conditional on a negative PCR result.”
“Overall, 1286 close contacts were identified for index cases testing positive for SARS-CoV-2 between January 14 and February 9, with 83% (244/292) of cases having at least one close contact. Ninety-five percent of close contacts were followed 12 days or longer.”
among these contacts 98 tested PCR positive for SARS-CoV-2 infection, and 1 had presumptive infection. Excluding those with a missing test result, the secondary attack rate was 14.9% (95% CI 12.1,18.2) among household contacts and 9.6% (95%CI 7.9,11.8) overall. In multivariable analysis household contact (OR 6.3, 95% CI 1.5, 26.3) and travelling together (OR 7.1, 95% CI 1.4, 34.9) were associated with infection.
“Notably, the rate of infection in children under 10 (7.4%) was similar to the population average (7.9%).” This really sheds new light on the epidemiology.
“The mean number of secondary cases caused by each index case (i.e., the observed reproductive number, R), was 0.4 (95% CI 0.3,0.5). The distribution of personal reproductive numbers was highly overdispersed, with 80% of infections being caused by 8.9% (95% CI 3.5,10.8) of cases (negative binomial dispersion parameter 0.58, 95% CI 0.35, 1.18).”
That actually means that transmissibility within households in this region was not that high. Of note, this is with all persons aware of being close to an index case and any transmission outside the household setting was not counted. Thus, the true effective R will be somewhat higher, but not above 1, as transmission seems to be well controlled in the region. To me, this sounds as good news, with 3 caveats.
First, to control spread in the population it helps to identify a large proportion of all infected subjects. Given the activities they employed in their “symptom-based surveillance” they probably did, but I wonder how reproducible those activities are. Second, “80% of infections caused by 8.9% of cases” reflects the relevance of superspreaders. Missing them in surveillance, may give the virus a jump start into a population, as apparently occurred in South-Korea and may be in Italy. And third, the infection rate was similar in children as in adults. That still doesn’t proove that children transmit the virus, but we can no longer assume that they don’t transmit.
We know what to do (but can we do what we know?).
One other thing we could learn from China: “This work was conducted in support of an ongoing public health response, hence was determined not to be human subjects research.”
Bye the way: We submitted a protocol for testing BCG vaccination in healthcare workers in order to prevent infection and disease symptoms due to SARS-CoV-2, today.