COVID-19 is an “evolving epidemic” and it has started posing a few challenges to public health officials, bringing in the need for detailed investigation. If persons testing positive for COVID-19 after the incubation period is one challenge, understanding the transmission dynamics is another, they said.

According to the World Health Organisation, most estimates of the incubation period — the time between catching the virus and one begins to have symptoms of the disease — range from one to 14 days. When a few States had a quarantine period of 14 days, Tamil Nadu doubled the number of days, fixing it at 28. In one way, this has proved right, as a few persons have tested positive even after 20 days, said officials.

There were a few cases in Tamil Nadu in which persons tested positive after the estimated incubation period of 14 days, said officials. “We have had a few such cases. For instance, patients have tested positive on the 16th and 20th day. This is why Tamil Nadu had decided to have a double quarantine period of 28 days, right from the start. We are now taking up detailed investigations of such cases. There are chances that these persons picked up the infection from others but we need to investigate to know the reason,” an official said.

Official sources said that persons testing positive at a later point were posing a puzzle. There were similar occurrences in Kerala too. “It is challenging, but COVID-19 is an evolving epidemic,” another official said.

Transmission dynamics

Transmission dynamics is another challenge. Health officials said that some persons who had attended the conference in Delhi tested negative for COVID-19, while their family members tested positive for the virus. In such instances, those testing negative too were put under isolation. “We need to understand transmission dynamics during the asymptomatic period. Who is testing negative is important, and whether the person is capable of transmitting the virus should be looked at,” he added.

Age is also a factor, said officials. “The individual’s immunity response too plays a role,” an official said.

Officials cited these as the reason why they continue insisting on strict adherence to home quarantine norms.