Study Finds Most Asymptomatic COVID-19 Patients Were Not Infectious

One of the many unanswered questions surrounding COVID-19 is why some infections are severe and even fatal while others are asymptomatic. And if an individual does have asymptomatic COVID-19, how infectious are they?

For the last 3 years, many hospitals implemented COVID-19 testing upon admission to evaluate whether transmission precautions are needed. A study presented at this week’s Society for Healthcare Epidemiology of America (SHEA) 2023 Spring Conference sought to determine if asymptomatic COVID-19 patients are actually infectious, and thus the necessity of hospital COVID-19 testing and precautions.

The study, presented by Stanford University immunocompromised infectious disease fellow Ralph Tayyar, MD, described the characteristics of asymptomatic COVID-19 patients. Tayyar and his team utilized a 2-step rPT-PCR specific to the minus strand of the SARS-CoV-2 envelope gene.

From July 2020-April 2022, the investigators reviewed the records of patients with a positive PCR test who were also tested for the strand-specific SARS-CoV-2 PCR within 2 days of admission to Stanford Health Care. This yielded a study size of 242 asymptomatic patients. The investigators calculated the percent of detectable minus strand-specific tests among asymptomatic patients over time, performing descriptive statistics to account for age, sex, and immunocompromised status.

Overall, 36% of PCR-positive inpatients were asymptomatic. Among the 242 asymptomatic patients, the average age was 56 years. This cohort was also 55% male, 21% immunocompromised, and 12% had been admitted for a surgical procedure. A total of 9% of the patients had detectable minus strand-specific assays.

Strand-specific rPT-PCR testing helped the investigators determine the majority of asymptomatic COVID-19 patients were noninfectious. Indeed, only 4-25% of asymptomatic inpatients had a detectable minus strand.

“Our findings agree with prior studies which have identified persistently positive SARS-CoV-2 PCRs without the presence of culturable live virus,” the study authors wrote. “Hospitals using SARS-CoV-2 PCR admission testing may need to reevaluate the continued use of this practice.”

They noted that a COVID-19 infection, even if asymptomatic, often delays care for hospital inpatients. Thus, the investigators emphasized the importance of confirming infectiousness and the real risk posed by asymptomatic COVID-19 infection.