One-in-three SARS-CoV-2 infections appear to be asymptomatic and nearly three-quarters of people without symptoms who receive a positive PCR test will remain asymptomatic, findings from a newly published research review suggest.
Writing in Annals of Internal Medicine, investigators Eric J. Topal, MD, and Daniel P. Oran of Scripps Research Translational Institute, La Jolla, California, noted that the review findings make a strong case for altering control strategies for Covid-19 to better account for asymptomatic transmission risk.
“Frequent, inexpensive, rapid home tests to identify and contain pre-symptomatic or asymptomatic cases — along with government programs that provide financial assistance and, if necessary, housing to enable infected persons to isolate themselves — may be a viable option,” they wrote. “And as the first generation of SARS-CoV-2 vaccines is deployed, more research will be needed to determine their efficacy in preventing asymptomatic infection.”
The research review, published online January 22, included observational studies and reports of mass screening for SARS-CoV-2 that were either cross-sectional or longitudinal in design, published through Nov. 17, 2020.
The studies also involved SARS-CoV-2 nucleic acid or antibody testing of a target population, regardless of current symptomatic status, over a defined period.
A total of 61 eligible studies and reports were identified, including 43 involving PCR testing of nasopharyngeal swabs to detect current SARS-CoV-2 infection and 18 that used antibody testing to detect current or prior infection.
In the 14 studies with longitudinal data reporting information on the evolution of symptomatic status, nearly three quarters of participants who tested positive but had no symptoms at the time of testing remained asymptomatic.
Topal and Oran noted that the heterogeneity of the studies precluded quantitative summaries using meta-analysis.
“We summarize the evidence in terms of the number of studies and the range, median, and interquartile range (IQR) for persons who tested positive but had no symptoms at the time of PCR testing or who reported having had no symptoms before or at the time of antibody testing,” they wrote.
Thirty of the studies included a list of specific symptoms, and many of the other studies used a variation of the catch-all phrase, “symptoms compatible with Covid-19,” the researchers noted.
Among the 43 studies using PCR testing, the proportion of persons who tested positive but had no symptoms at the time of testing ranged from 6.3% to 100%, with a median of 65.9% (IQR, 42.8% to 87.0%).
Twenty-four of the 43 collected cross-sectional data and reported only the symptomatic status at the time of testing, so the researchers were unable to distinguish between pre-symptomatic and asymptomatic cases. In these studies, the proportion of persons who tested positive but had no symptoms at the time of testing ranged from 40.7% to 100%, with a median of 75.5% (IQR, 50.3% to 86.2%).
Nineteen of the PCR-based studies collected data on symptoms longitudinally after testing, making it possible to distinguish between pre-symptomatic and asymptomatic infection. The follow-up period in these studies ranged from 2 to 70 days, with a median of 14 days (IQR, 14.0 to 15.8 days) and the proportion of people who tested positive and remained asymptomatic ranged from 6.3% to 91.7%, with a median of 42.5% (IQR, 29.6% to 77.8%).
The Real-time Assessment of Community Transmission (REACT) study, conducted in England, was the largest study included in the review, with data on 932,072 people in the country following nationwide nucleic acid and antibody testing for SARS-CoV-2. Nationwide testing was implemented in May of 2020 for everyone over the age of 5 years in multiple phases, and the review combined the results of 6 phases of nucleic acid testing.
At the time of testing, 47% of those who tested positive for SARS-CoV-2 (1,425 of 3,929 people) had no symptoms, but no longitudinal data were collected to distinguish between pre-symptomatic and asymptomatic cases.
Topal and Oran noted that the highest-quality evidence included in the review came from large-scale studies using antibody testing that were designed to achieve representative samples of nationwide populations in England and Spain.
“It is remarkable that these independently conducted serosurveys yielded nearly identical proportions of asymptomatic SARS-CoV-2 infections; 32.4% in England and 33.0% in Spain,” they wrote.
- One-in-three SARS-CoV-2 infections appear to be asymptomatic, according to a review of 61 studies.
- Nearly three-quarters of people without symptoms who receive a positive PCR test will remain asymptomatic, the research review found.
Salynn Boyles, Contributing Writer, BreakingMED™
This research was funded by the National Institutes of Health. Researchers Eric J. Topal and Daniel P. Oran reported no relevant disclosures.
Cat ID: 125
Topic ID: 79,125,730,125,190,926,927,151,928,934