Since the first report of pneumonia clusters caused by a novel coronavirus in Wuhan at the end of 2019, there have been more than five million confirmed cases of COVID worldwide. The novel coronavirus designated as SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) is responsible for the pandemic of COVID-19, which stands for CoronaVirus Disease 2019. COVID-19 is a viral infection of the respiratory system, The symptoms of Corona are fever, cough, fatigue, shortness of breath, sore throat, loss of appetite, diarrhoea, loss of smell sensation and lack of taste. When infected individual talks, coughs or sneezes, tiny droplets that contain the virus are caught up in the air and enter other healthy individuals through their nose, eyes or mouth. Once in the human body, the virus latches onto the human cell with the crown-like spikes present on the surface of the virus and enters into the cell. The virus then hijacks the cell with its viral RNA to make more copies of itself. As more viruses are produced, the individual becomes infected and the infection cycle repeats. Besides, experts found that the virus is able to survive on inanimate surfaces for hours. This increases the chances of getting infected as people can unknowingly pick up the virus while touching public surfaces and their own faces. For this reason, the virus was able to spread rapidly, exponentially increasing the cases globally.
The implementation of effective COVID-19 testing service by the local health authority is critical in order to flatten the curve of infection rates. This is evident in South Korea as their prompt action of massive testing done throughout the nation managed to track down all the infected individuals. Regardless of manifesting the symptoms or not, once confirmed COVID-19, they were isolated, treated, and were tracked further for contact tracing. The fact that the massive testing for COVID-19 is a major success in reducing the spread of infection not only shows that COVID-19 test can be positive for infected asymptomatic individuals but also implies that infected individuals who show no symptoms are capable of spreading the virus. There are two scenarios in which an infected person can have no symptoms; either the person was recently exposed to the virus and is still in the incubation period, or the person has a true asymptomatic infection, one which never develops symptoms but carries the virus. Several studies suggest that asymptomatic infections are common. In fact, some have been well documented.
When a cruise ship in China was found to have the COVID-19 outbreak, nearly all the passengers and staff were tested for SARS-CoV-2. While 17% on board were tested positive, about half of them were asymptomatic at the time of diagnosis. A modelling study estimated that 18% were true asymptomatic cases, although this was based on assumptions and had included incubation period. The incubation period of COVID-19 is thought to be 14 days, but most cases happened within four to five days after exposure.
Another study involving a smaller COVID-19 outbreak in a nursing facility found that 27 of the 48 residents were tested positive but were asymptomatic at the time of diagnosis. While 3 infected residents had true asymptomatic infections, 24 of them were found to have developed symptoms over the next seven days, suggesting that the testings were done early while they were still in the incubation period.
There were other studies that recorded a higher proportion of asymptomatic cases. For instance, in a report of a universal screening program for pregnant women in New York hospitals that use reverse transcription-polymerase chain reaction (RT-PCR) test on nasopharyngeal specimens, 29 out of 210 asymptomatic women were found positive with SARS-CoV-2 infection. That is 14% of infected individuals without fever. Also, the study had an addition of four symptomatic women who tested positive. This means of the 33 women who tested positive for SARS-CoV-2, 88% of them were asymptomatic on presentation.
In short, you can test positive for COVID-19 even if you are asymptomatic.