Asymptomatic COVID-19 patients still carry the same amount of virus

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A study conducted by Soonchunhyang University Bucheon Hospital in Seoul, South Korea, has given results that indicate that asymptomatic COVID-19 patients can carry as much of the virus as patients who show symptoms.

South Korea started mass testing throughout their population in March 2020 and this enabled them to identify patients who were asymptomatic early on. People that tested positive for coronavirus were monitored in a treatment center, with scientists taking regular nasopharyngeal swabs to detect how much of the virus they were carrying. Only once the tests came back negative were the patients released.

Over this period 1,886 tests were carried out on 303 patients and the results suggested that patients that showed no symptoms, either at the time of the test or later on, had the same amount of detectable viral material as those patients that were displaying symptoms.

The virus was detected in the asymptomatic cohort for a significant length of time, although it did appear to pass from their systems slightly faster than from the systems of patients who did show symptoms; 17 days and 19.5 days from diagnosis to a negative test result, respectively.

This study, published in JAMA Internal Medicine,  is invaluable as one of the only studies to provide data on asymptomatic patients, so can provide insight into the role of these cases in transmission of the virus. However, the researchers do point out that the isolation center did not take patients with more severe cases of COVID-19 and those included were generally younger and more healthy than average patients.

The data has prompted much discussion on whether asymptomatic patients play a key role in transmission of the virus. In theory, by having the same amount of viral material in the nose and throat as a symptomatic patient means that there is the same amount of material to be passed on. However, without the characteristic cough, infected droplets are less likely to be emitted into the air.

There is “as much virus in their respiratory mucus as someone who has the disease”, stated Simon Clarke, a cellular microbiologist at the University of Reading (UK).

Clarke added: “that doesn’t mean they’re spraying as much into the environment”. Indicating that someone who was symptomatic was still more likely to be at a higher risk of transmitting the virus.

Andrew Preston from the University of Bath (UK) explained that the risk of passing on the virus could depend on many factors, including how deeply the infected individual was breathing, their proximity to other people and whether they were in a closed or open environment.

The conclusions of the study still recommended that asymptomatic patients isolate to help control the spread of SARS-CoV-2.

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Sources: Lee S, Kim T, Lee E et al. Clinical course and molecular viral shedding among asymptomatic and symptomatic patients with SARS-CoV-2 infection in a community treatment center in the Republic of Korea. JAMA Intern. Med. doi:10.1001/jamainternmed.2020.3862 (2020) (Epub ahead of print); www.bbc.co.uk/news/health-53665008

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