The recent WHO statement that it is ‘rare’ for asymptomatic coronavirus-infected individuals to transmit the disease to other individuals has raised concern among researchers and public health experts. Here’s a deeper dive into the question of asymptomatic transmission.
- The proportion of infected individuals who remain asymptomatic is not known. One reason is that people don’t generally seek testing unless they feel unwell. The only indications come from outbreaks in closed settings — such as prisons, meatpacking plants, nursing homes and cruise ships — where mass testing has been possible. People may also not always be the best judge of their condition — having “no symptoms is in the eye of the beholder. And, without adequate followup (which does not exist), “asymptomatic” people might merely be “presymptomatic”.
- Cases of onward transmission from asymptomatic individuals may be rare but it does happen, and researchers are divided on whether such cases indicate a broader trend or is an anomalies. Studies have shown that asymptomatic infected people have similar numbers of virus particles in their throats as people who feel unwell, although they are not spewing them as readily because they are not coughing or sneezing. Speaking and breathing forcefully in proximity to others — e.g. singing in a choir, panting from exertion at a gym, or shouting to be heard in a setting like a nightclub — have all been implicated in transmission.
- So we are really talking about an “undetected positive” category comprising the asymptomatic infected, the presymptomatic, and the people who do not realize they feel unwell. It is likely that the virus is being transmitted in undetected cases before the individual can be identified and contained. Despite the misleading WHO statements, we must continue to employ the effective tools we have at our disposal — hand washing, facial coverings, and social distancing.
— Via NPR