The study has major implications for judicious resource use as epidemic nears the peak and health system capacity is stretched. While in Wuhan, every patient with mild illness was isolated in the hospital or other isolation facilities for a prolonged period, this is not feasible everywhere. Hence, countries are isolating such patients at home. This increases the risk of household contacts considerably – a choice between devil and deep sea! This has to be complemented with isolation of the subject within a room in the house and other protective measures. It is also clear that contact tracing could focus on the contacts near or even before symptom onset of the index cases when the number of index cases or contacts is too large for all contacts to be traced, given the available resources.
- The study reiterates the fact that the maximum infectivity window for COVID-19 is 4 days before onset of symptoms to 5 days after that.
- Close contacts were tested only when symptomatic or had high risk. This would have underestimated the secondary attack rate. Ideally all contacts should have undergone RT-PCR tests.
- The current study reports nil asymptomatic transmission. However, there have been case reports on asymptomatic transmission. According to WHO there is inconclusive evidence whether such transmission occurs.
- Limited data on pre-symptomatic transmission as data was collected mostly after symptoms started to appear in the index cases.
Article: Cheng H, Jian S, Liu D, et al. Contact Tracing Assessment of COVID-19 Transmission Dynamics in Taiwan and Risk at Different Exposure Periods Before and After Symptom Onset. JAMA Intern Med. Published online May 01, 2020. doi:10.1001/jamainternmed.2020.2020Epidemiology-Contact tracing and risk at different exposure periods