Recently, we have been seeing some cases of confirmed novel coronavirus (COVID-19) patients without travel history or known contacts with other confirmed COVID-19 patients. Does that imply invisible chains of infection could be happening within the community? For cases with no obvious source of infection, is it possible that the patient caught the virus from an “invisible” patient who is in the incubation period?
What is incubation period?
Incubation period is the time interval between the initial contact with an infectious agent, such as virus, and the appearance of the first sign or symptom of the disease. During this period, the virus will continue to replicate in the person’s body. Different infectious diseases have different incubation periods. For instance, with hand, foot and mouth disease, the incubation period is typically 3 to 5 days. For chicken pox, it is typically 10 to 21 days, and for SARS, it is 7 to 10 days. As for COVID-19, based on the current scientific evidence, patients most commonly present their symptoms 5 to 7 days after contracting the virus, but in some cases, it could be as long as 14 days or even up to twenty something days. For the time being, most health authorities usually regard the incubation period of COVID-19 as 14 days.
Do patients exhibit symptoms during the incubation period?
There are no symptoms exhibited during the incubation period, hence making it difficult to detect. This explains why when a case of COVID-19 is confirmed, it is essential to trace all the close contacts of the patient and require those people to be quarantined. If the person under quarantine does not fall ill after one incubation period of 14 days, then it is regarded as safe to say that the person is not infected. This said, exceptions do occur.
Is a person infectious during the incubation period?
This depends on the type of infection. Using measles as an example, patient can spread the virus during the incubation period. As for COVID-19, there have been some reports that patients within the incubation period who have not exhibited any symptoms can also spread the virus. As there are only very few reported cases, it is inconclusive and not supported by large epidemiological studies at this stage.
In contrast to SARS, we are now dealing with an infection that has a longer incubation period, and there is an uncertainty as to whether a virus carrier could spread the virus during the incubation period, both of which will make the prevention of the epidemic more difficult. Having said that, rather than going into a panic mode, we should remain vigilant with our personal hygiene and avoid going to crowded areas to minimise the chance of getting infected.
Dr Alexander Chiu, Medical Director, Health and Employee Benefits, AXA Hong Kong and Macau