About a fifth of people infected with COVID-19 are asymptomatic – although the proportion may be greater among health workers, according to new studies.
The first study was carried out by Professor Sung-Han Kim of Asan Medical Centre, Seoul, Republic of Korea, and colleagues.
They explored the possibility that asymptomatic individuals can significantly contribute to the community spread of the infection. The team looked at 213 patients with COVID-19 without severe symptoms and found that 19% were asymptomatic.
This group had “comparable viral loads”, they report in the BMJ today (23 September).
“Asymptomatic individuals were frequent among those infected with SARS-CoV-2, but harboured a comparable viral load compared with that of symptomatic patients and may thus act as a meaningful driving force for the community spread of COVID-19,” they conclude.
For the second piece of research, a team from the University of Bern, Switzerland, systematically reviewed 79 studies from a database of COVID-19 evidence collected from March to June 2020.
This included 6,616 people, of whom 20% were estimated to have been asymptomatic.
Details appeared yesterday (22 September) in PLoS Medicine. Dr Diana Buitrago-Garcia explains that accurate estimations are critical to understanding population level transmission, and for appropriate public health strategies.
The authors write: "The findings of this systematic review of publications early in the pandemic suggests that most SARS-CoV-2 infections are not asymptomatic throughout the course of infection.
“The contribution of presymptomatic and asymptomatic infections to overall SARS-CoV-2 transmission means that combination prevention measures, with enhanced hand and respiratory hygiene, testing and tracing, and isolation strategies and social distancing, will continue to be needed.”
But a third study, presented to a European conference yesterday, found that up to 40% of healthcare workers found to be carrying the virus were asymptomatic.
Swiss researchers reported their findings to the special conference of the European Society of Clinical Microbiology and Infectious diseases on coronavirus diseases.
The findings come from 97 studies of 230,000 health care workers in 24 countries. From PCR and antibody testing, the prevalence of COVID-19 infection was between seven and 10%. 25% of these were doctors and 48% nurses.
Researcher Professor Oscar Franco, from the University of Bern, Switzerland, said: "Health care workers are at the frontline response to the new coronavirus disease 2019 (COVID-19), exposing themselves to a higher risk of acquiring the disease, and subsequently, exposing patients and colleagues.
"Because we might miss a large proportion of COVID-19 cases if screening targets only symptomatic health care workers, universal screening for all exposed health care workers regardless of symptoms should be the standard strategy. While more research is needed to understand specific interventions that can help reducing SARS-CoV-2 infection among healthcare personnel, it is clear that providing healthcare workers with adequate personal protective equipment and training is essential."
https://thorax.bmj.com/lookup/doi/10.1136/thoraxjnl-2020-215042
Ra, S. H. et al. Upper respiratory viral load in asymptomatic individuals and mildly symptomatic patients with SARS-CoV-2 infection. Thorax 23 September 2020 doi: 10.1136/thoraxjnl-2020-215042
http://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1003346
Buitrago-Garcia, D. et al. Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis. PLoS Medicine doi: 10.1371/journal.pmed.1003346
https://academic.oup.com/aje/advance-article/doi/10.1093/aje/kwaa191/5900120
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