One reason why containing novel coronavirus spread is challenging is that people who seem to be healthy despite being infected with the virus can spread it to others. A body of evidence now suggests that people without symptoms can and do readily spread coronavirus, and people are most infectious just a couple of days before symptoms show up. This is typically the presymptomatic phase when infected people don’t exhibit symptoms but do shed substantial amounts of virus.
A retrospective study of 303 symptomatic and asymptomatic patients infected with SARS-CoV-2 during March 6-26 has found definite evidence that people who do not exhibit symptoms carry the same amount of virus as those who are symptomatic. The results of the study carried out in South Korea were published in the journal JAMA Internal Medicine.
Of the 303 patients studied, 110 (36.3%) were asymptomatic at the time of isolation. The team, led by Dr Eunjung Lee from the Soonchunhyang University Hospital, Bucheon, South Korea, found that only 21 of 110 asymptomatic patients subsequently developed symptoms.
This study thus provided the much-needed evidence that many people with coronavirus infection can remain asymptomatic for a “prolonged period”.
While this study found that 29% of asymptomatic patients never developed symptoms at all, Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases, had pegged it at 20-45%. A review in the Annals of Internal Medicine states that asymptomatic persons account for nearly 40-45% of SARS-CoV-2 infections. The review also said that such people transmit the virus for an “extended period, perhaps longer than 14 days”.
While the incidence of asymptomatic patients carrying high viral load raises the possibility of such people spreading the virus to others, the study did not determine this, as it was not designed for the said purpose. Both symptomatic and asymptomatic patients were isolated, thus providing no opportunity to study the chain of transmission. Also, live virus was not cultured (grown) in labs to confirm the infectious nature of the virus. Hence, they note that “detection of viral RNA does not equate infectious virus being present and transmissible”.
While several studies too have found a large percentage of asymptomatic cases, such studies have a limitation. Unlike the current study, earlier ones had considered presymptomatic patients as asymptomatic without observing the clinical course of asymptomatic cases.
The challenge with asymptomatic infection is the heightened risk of such people travelling freely and mingling with others thus spreading the virus to them, whereas those with symptoms are more likely to stay at home.
The combination of prolonged period of being asymptomatic and carrying similar viral load as people with symptoms would necessitate isolation of all infected people regardless of symptoms, they note. “An important implication of our findings is that there may be substantial underreporting of infected patients using the current symptom-based surveillance and screening,” they write.
The study once again underscores the importance of wearing masks and maintaining physical distancing to reduce the chances of getting infected. Studies have shown that universal masking reduces the amount virus inhaled thus increasing the chances of coming down with only mild disease even when infected.
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