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About 20% of asymptomatic people who test positive for COVID-19 will remain symptom-free over time, according to two studies published Sept. 22 in a separate journal. Therefore, the investigators propose that most asymptomatic patients should be considered asymptomatic.
“Only a small proportion of people with SARS-CoV-2 have completely asymptomatic infection. Most patients with SARS-CoV-2 who are asymptomatic at the time of testing will continue to develop symptoms,” study author Nicola Low, MD, chiefs. from the Research Group at the Institute of Social and Preventive Medicine at the University of Bern in Switzerland, said Medscape Medical News.
The results also suggest expanded testing for SARS-CoV-2 infection is needed, especially among those at high risk, and supports the use of control measures including masks, physical distancing and isolation.
“People with asymptomatic infections are contagious. All should be isolated and contact tracing must be initiated,” added Low.
Low and colleagues did a systemic review and live meta-analysis evaluating the occurrence and transmission of asymptomatic and presymptomatic patients. They publish their findings on PLOS Medicine.
Sung-Han Kim, MD, PhD, and fellow researchers did a studies comparing SARS-CoV-2 levels in the nose and throat of asymptomatic vs symptomatic individuals published in the journal Thorax.
Research teams from Switzerland and South Korea point to the need for more clarity about asymptomatic vs asymptomatic patients with COVID-19. Most researchers had previously tested people for SARS-CoV-2 infection at one time, preventing identification of the percentage who later developed symptoms.
Previous work is also heterogeneous. “Researchers have investigated the proportion with asymptomatic infections in various settings, including hospitals, as part of the outbreak, through contact tracing, and through screening,” Low said. The variability between estimates was “very high,” from 3% to 83% in individual studies, he added.
Main Meta-Analysis Findings
Low and colleagues searched PubMed, Embase, bioRxiv and MedRxiv for relevant studies. The “live” meta-analysis reflects the updates that were taking place in March, April, and June this year. They used reverse transcriptase polymerase chain reaction (RT-PCR) testing for SARS-CoV-2.
The data included a statistical modeling study of all 634 passengers from Diamond Princess cruise ship with a positive RT-PCR test result.
Overall, in 79 studies conducted in a variety of different settings, 20% of people with SARS-CoV-2 infection remained asymptomatic during follow-up.
When restricted to seven studies that screened the population as defined by follow-up, a higher proportion (31%) remained asymptomatic over time.
The investigators caution that their asymptomatic estimate is limited by bias in the study design. In addition, they found it difficult to identify the proportion of asymptomatic patients who contributed to SARS-CoV-2 transmission as a whole.
Part of the five studies includes detailed contact tracing. From this data, the researchers calculated the risk of asymptomatic people transmitting SARS-CoV-2 (summary risk ratio, 0.35, compared to people with symptoms of 0.63). More trials are needed to confirm these findings, they wrote.
“The findings from the systematic review, including ours, do not support the claim that most SARS-CoV-2 infections are asymptomatic,” they added. Furthermore, because SARS-CoV-2 can be transmitted several days before an infected person develops symptoms, “asymptomatic transmission is likely to have contributed substantially to the SARS-CoV-2 epidemic as a whole.”
Similar Viral Load Found in South Korea
Kim and colleagues found that in nearly the same proportion, 19% of the 213 patients, without severe COVID-19 symptoms, remained asymptomatic through potential exposure, laboratory confirmation, and hospital admission.
Upper respiratory tract viral load did not differ significantly between asymptomatic and asymptomatic individuals in South Korean upper respiratory tract samples.
“Our data adds to the recent growing evidence that asymptomatic individuals with SARS-CoV-2 infection do indeed contribute to the ongoing community spread of COVID-19, senior study author Kim told Medscape Medical News.
The SARS-CoV-2 gene’s cycle mean threshold (Ct) value, which reflects viral load, “was very similar between asymptomatic individuals and symptomatic patients,” added Kim, professor of infectious diseases and head of the Office for Infection Control at Asan Medical Center at Asan Medical Center. Seoul South Korea.
These findings suggest that asymptomatic individuals have “comparable potential to transmit the virus to as many symptomatic patients,” he said. “To prevent transmission from asymptomatic individuals with SARS-CoV-2 infection, the use of face masks by the general public – regardless of symptoms – is strongly recommended.”
The study was feasible because of the unique situation – the COVID-19 outbreak in Daegu City was traced to one religious group. 3000 close contacts identified reported symptoms as being absent to severe, and asymptomatic people were isolated and monitored in specialized facilities.
“We were able to assess many asymptomatic individuals who were unlikely to be identified as cases of COVID-19,” wrote the investigators.
Most of the 183 patients, including 39 asymptomatic and 144 asymptomatic, underwent a follow-up RT-PCR test. Swab samples from the nasopharynx and oropharynx were combined in one test.
As most asymptomatic people with COVID-19 continue to live in a community setting, the researchers note, “such people can act as important drivers for the spread of the COVID-19 community and the state of the ongoing pandemic.”
The limitation of this study is that the population consists mainly of individuals in their 20s and 30s, so generalization to other age groups is unknown.
“This study represents a valuable contribution, but also underscores how much uncertainty remains. There isn’t much to say about asymptomatic transmission,” Jonathan Dushoff, PhD, professor, Department of Biology, McMaster University, Hamilton, Canada, told Medscape Medical News when asked to comment on research.
“In my opinion, they don’t change the consensus that people without symptoms, whether asymptomatic or asymptomatic, should be seen as potential transmitters, despite weak evidence that they are less contagious than people with symptoms,” added Dushoff, who one of the study authors about the timing of transmission of SARS-CoV-2 asymptomatically published in June in the journal Epidemic.
Not an Easy Task
“It would actually be difficult and challenging to provide a true estimate of the asymptomatic transmission rate,” says Lei Huang, MD, Medscape Medical News when asked for comment. People without symptoms may not realize they were exposed to other people during the virus incubation period, Huang added.
Studying randomly selected populations, which are representative and generalizable to settings where disease transmission is known to occur, would be a more ideal approach, Huang said.
Current research “shows that in places where transmission has occurred, it is always beneficial to pay special attention to self-protection, even when dealing with someone who appears to be very healthy,” said Huang, the lead author of the study. prospective, contact tracing study which revealed the rapid transmission of COVID-19 in asymptomatic people aged 16 to 23 years.
“While the likelihood of transmission from asymptomatic cases may be lower than from symptomatic cases, the importance of asymptomatic transmission should not be overlooked given the uncertainty of the true proportion of asymptomatic cases,” said Huang, who is affiliated with the Department of General Surgery. , The First Affiliated Hospital of Anhui Medical University, Anhui Province, China.
Low is a member of the editorial board of PLOS Medicine. Kim, Dushoff, and Huang did not disclose the relevant financial relationships.
The Swiss National Science Foundation, the European Union Horizon 2020 research and innovation program, the Swiss government excellence scholarship, and a grant from the Swiss School of Public Health Global P3H fund the study of PLoS Medicine.
A grant from the Korea Health Technology Research and Development Project through the Korea Health Industry Development Institute, funded by the Ministry of Health & Welfare, Republic of Korea, supports research on Thorax.
PLOS Med. Published online 22 September 2020. Full text
Thorax. Published online 22 September 2020. Full text
Damian McNamara is a staff member journalist based in Miami. It covers a wide range of medical specialties, including infectious diseases, gastroenterology, and primary care. Follow Damian on Twitter: @Detikcom.
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