Asymptomatic, but dangerous
Scientists compared the number of viral particles in SARS-CoV-2 carriers with and without symptoms
Maria Azarova, Naked Science
A team of American scientists from the Broad Institute analyzed the viral load in hospitalized patients with Covid-19, as well as in asymptomatic carriers of the coronavirus. The results of the work are published on the preprints website medRxiv.org (the study has not yet been reviewed).
One of the main problems of the Covid-19 pandemic is the huge number of asymptomatic patients. The spread of SARS-CoV-2 by people who do not have clinical signs of infection prevents the healthcare system from fighting the coronavirus disease and making diagnoses on time.
Until now, the distribution of viral load (a measure of the severity of infection, which is calculated by estimating the number of viral particles in a certain volume of the biological fluid of an infected organism) in people with and without symptoms remained uncertain. Meanwhile, this will help to fully assess the risks of transmission of the virus.
The new study was conducted with the participation of guests and staff of most nursing homes and some similar institutions in Massachusetts. "In the period from April 9 to June 9, 2020, we tested smears taken from the nasopharynx in 32,480 people. <...> In addition, we extracted RNA and tested for SARS-CoV-2 by reverse transcription polymerase chain reaction. A total of 2,654 nursing home residents (15.5%) and 624 employees (4.1%) tested positive for SARS-CoV-2. 12.7% of guests and 3.7% of staff without symptoms were diagnosed with SARS-CoV-2 – compared with 53.1% of residents and 18.2% of staff with symptoms", – the authors of the work write.
According to the results of a large-scale analysis, scientists report that "strikingly similar viral load distributions" were found in patients with or without symptoms who were tested. Moreover, the similarities were most noticeable during the peak of the epidemic in Massachusetts.
"In aggregate, the distribution of viral load was very similar, with a statistically but not significantly different mean value, between populations with and without symptoms over the entire time period, across all the subcategories studied (age, race, ethnicity, gender, resident/staff). The average values were indistinguishable between these groups during the peak of the outbreak in Massachusetts, but the gap appeared later, during the survey period by the end of May, when the epidemic began to subside," the scientists note.
In their opinion, since the distribution of viral load in infected people, regardless of symptoms, is similar, existing RNA testing methods that have been confirmed to detect SARS-CoV-2 in patients with clinical signs of Covid-19 should also work for those who at first glance seem healthy. Finally, the findings of the new work confirm that asymptomatic carriers are dangerous for healthy people almost to the same extent as everyone else infected with coronavirus.
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