The lack of testing in asymptomatic carriers makes it harder to control SARS-CoV-2 spread, according to researchers at the Georgetown Center for Global Health Science and Security, Georgetown University in Washington.
Two groups of individuals dominate the transmission of COVID: asymptomatic carriers, who do not develop any symptoms throughout the course of their infection; and presymptomatic carriers, who develop symptoms a few days after being infected.
Transmission without symptoms makes it difficult to estimate the infectious timeline and potential exposures. Asymptomatic cases may likely mingle with others oblivious to their infection, promoting virus spread. They may also not adhere to social distancing, mask wearing etc. Contact tracing is vital to monitor the spread of the disease, and asymptomatic cases makes surveillance to analyse secondary attack rates highly challenging.
Though there is no accurate reporting on the prevalence of asymptomatic cases available, early studies showed that they made up so 30% to 80% of infections. More recent evidence put asymptomatic cases at 17% to 30% of infections.
In COVID cases, the infectious period begins two days before symptom onset and several days thereafter, though viral shedding is reduced in the first week of symptoms.
Viral shedding in asymptomatic cases is poorly understood, however it is known that asymptomatic cases have the same viral load as symptomatic cases, regardless of severity. In asymptomatic individuals, infectious periods are shorter due to reduced titers at peak replication and faster viral clearance.
Some studies have shown that asymptomatic individuals are 42% less likely to infect others and have lower secondary attack rates, while other research indicates that, despite the shorter infectious periods, asymptomatic individuals have similar transmissibility to those who are presymptomatic.
The researchers note that symptomatic individuals were motivated to seek testing, treatment and self-isolate upon feeling COVID symptoms.
“With many contagious people experiencing no symptoms and in the absence of robust surveillance testing for asymptomatic or presymptomatic infections, it is critical to maximising efforts to reduce transmission risk in the community,” noted the researchers.
Source: Medical-News.Net
Journal information: Rasmussen, A., and Popescu, S. (2021). SARS-CoV-2 transmission without symptoms. Science. https://science.sciencemag.org/content/371/6535/1206
