Can COVID-19 incubation period go beyond 14 days?

Health experts are concerned after three people test positive for the infection even after completing 23 days of self-isolation and have tested negative two weeks ago

Published: 27th April 2020 05:33 AM 

File picture of COVID-19 outpatients ward set up at Kilpauk Medical College Hospital in Chennai

By OMJASVIN M D

Express News Service

CHENNAI: Can incubation period for the novel coronavirus go beyond the 14 days as stated by health experts? This question has become all the more relevant in Tamil Nadu as three people were tested positive for COVID-19 after completing 23 days of self isolation and having tested negative two weeks ago. This worrisome pattern has emerged in Tiruchy where a trio returned from Delhi on March 22. They have been quarantined ever since their return. According to the World Health Organization’s criteria, the incubation period for novel coronavirus usually ranges from 5 to 14 days. Going by this, the Tiruchy patients should have shown symptoms by April 5, that is 14 days from their arrival.

However, the asymptomatic trio was found to be positive only on April 18 after samples were taken from them on April 14. Similar trends have been noticed in Kerala’s Kannur and Palakkad districts where patients were found to be positive on 24th and 26th days respectively, while many others in that State tested positive even 20 days after their self isolation. Several patients in Andhra Pradesh too have carried the virus beyond three weeks.

However, virology expert Jacob John says 50 per cent of people would show symptoms within six days while most others would exhibit symptoms by 14 days. It is in most rare cases, people start showing symptoms even after 14 days and this can go up to 40 days. “In people who tested positive after 20 or 30 days since self isolation, it is unknown whether they had come in contact with some infected persons. These are very rare cases,’’ says John.

John points out that a conclusion can be arrived at only when the source of the infection is identified. He adds that inadequate testing could be a reason behind these cases as some people would be carrying the virus and remaining asymptomatic.

Dr Subramanian Swaminathan, senior consultant, Infectious Diseases, Gleneagles Global Health City, says young people sometimes may be asymptomatic and will be carrying the virus for longer periods. “Sometimes, PCR tests may show negative result when the infection is mild and the nasal-throat swab is not collected properly,’’ says Dr Subramanian.

The doctor says the PCR test is adequate for initial tests but may not be an ideal for follow up tests. He says the PCR test picks up the viral RNA but does not distinguish whether the virus is viable or non-viable.

“To find out whether the virus is transmissible or not, viral culture test has to be done in specialised laboratories,’’ says Dr Subramanian. The doctor affirms that the virus is the elephant in the room and testing must be ramped up across the State for faster identification.