Symptomatic transmission occurs from a person who is experiencing symptoms. Data published by epidemiology and virologic studies said COVID-19 is transmitted from symptomatic people to others infected through respiratory droplets by close contact with an infected person or by contact with contaminated surfaces or objects of an infected person. Data from clinical and virologic studies confirms shedding of the COVID-19 virus is higher in the upper respiratory tract (nose and throat) through a repeated collection of biological samples from infected patients. Compared to the later stage of this disease, people are more infectious at the time of early symptoms begins.
Pre- symptomatic transmission occurs from infected person before the onset of the symptoms. Pre-symptomatic transmission occurs through infectious droplets or by touching the contaminated surfaces. The period between virus exposure and symptom onset is known as the “incubation period or pre-symptomatic period” of COVID-19. During this period, some infected persons can be infectious. The average incubation period is 5-6 days, and sometimes it may be 14 days. The pre-symptomatic transmission has been documented in some cases reports, by tracing the contacts and investigating the cluster of confirmed cases. This data suggests that some people can test positive for COVID-19 in 1-3 days before the symptom onset.
Asymptomatic transmission is a transmission occurred from infected a person, who does not develop symptoms. There have been few reports for laboratory-confirmed cases as asymptomatic. But there is no documentation for asymptomatic transmission. In some countries, asymptomatic cases have been reported as part of connection tracking efforts.