Asymptomatic COVID-19 cases show need for wider surveillance testing, study suggests

A study in the New England Journal of Medicine is among the largest to examine the asymptomatic spread of the novel coronavirus. The study focused on 1,848 U.S.

A study in the New England Journal of Medicine is among the largest to examine the asymptomatic spread of the novel coronavirus. The study focused on 1,848 U.S. Marine Corps recruits aged 18-31 years who were instructed to quarantine at home prior to arriving at the Citadel military college in Charleston, SC. Once at the college, the recruits underwent a second 14-day supervised quarantine before starting their training. They were monitored daily for symptoms and were also tested within the first 2 days of arrival, on day 7, and on day 14. A total of 51 COVID-19 cases were identified by the prescheduled tests, but none were detected as a result of additional tests given to individuals who reported symptoms. Researchers also conducted genetic analyses on some of the infected volunteers' samples, finding six clusters where the viral genomes were extremely similar. Andrew Letizia, MD, one of the lead authors of the study and an infectious-disease expert at the Naval Medical Research Center, said: "This shows that even in the setting of very strictly enforced public-health measures put in place to mitigate spread, if you want to find the individuals who are infected with SARS-CoV-2, you really have to augment those public-health mitigation strategies with additional surveillance testing." Public-health experts say this involves testing people on a regular basis, whether they have symptoms or not. This can be done by testing people one by one, or through pooled testing, where several patient samples can be screened using a single test.