Universal SARS-CoV-2 screening in hospitals catches asymptomatic carriers of infection but yields a substantial number of false-positives, leading to unnecessary isolation, inappropriate treatment, and care delays, as shown in a large retrospective study.
Among 75,667 PCR saliva tests performed on 42,666 patients (median age 64 years, 50.6 percent female), infection was detected in 761 patients (1.2 percent). Results were true-positive in 483 patients (63.5 percent) and false-positive in 278 (36.5 percent). [JAMA Netw Open 2026;9:e265867]
Of the patients with a false-positive SARS-CoV-2 test result, 50 percent were placed in isolation during their hospital stay and 16.5 percent were placed in cohort wards where they were exposed to patients with true-positive SARS-CoV-2 infection. Surgical procedures and interventions were cancelled or postponed for nine patients (3.2 percent). Antiviral and immunomodulating drugs were administered to 70 patients (25.2 percent) based on symptoms initially considered compatible with COVID-19 and then later reassessed as being consistent with other underlying conditions.
“Our findings align with prior research suggesting that universal SARS-CoV-2 screening in healthcare settings can help identify asymptomatic carriers,” said first author Dr Marvin Weiss from the University of Basel, Basel, Switzerland, and colleagues.
However, the low test-positivity rate of 1.2 percent and the relatively high false-positive rate of 36.5 percent reflect the challenges of maintaining high specificity in low-incidence contexts, added Weiss and colleagues.
Factors associated with diagnostic performance
The study was conducted at the University Hospital Basel, wherein all patients with systematic screenings for SARS-CoV-2 infection from February 2021 to July 2021 and from August 2021 to December 2022 were included.
Weiss and colleagues found that the diagnostic accuracy of universal screening was influenced by local infection rates. The proportion of patients with false-positive test results recorded during weeks with high community incidence (ie, >150 events per 100,000 inhabitants) was lower than that documented during weeks with low community incidence (ie, <150 events 100,000 inhabitants), at 35.1 percent and 55.8 percent, respectively.
Additionally, screening test positivity correlated with wastewater viral loads.
“Our findings confirm that testing is more efficient and yields more positive results in settings with high community 7-day incidence, which aligns with guidelines of the European Society of Clinical Microbiology and Infectious Disease and the Society for Healthcare Epidemiology of America,” the authors noted. [Clin Microbiol Infect 2022;28:672-680; Infect Control Hosp Epidemiol 2023;44:2-7]
On the other hand, during periods of low community incidence, universal SARS-CoV-2 screening in hospitals may result in unintended negative consequences for patients. “This can strain healthcare systems and adversely affect patient outcomes,” they added.
Weiss and colleagues emphasized the importance of context-driven implementation, in which screening efforts are aligned with epidemiological trends and resource availability. “Wastewater-based epidemiology as a complementary surveillance tool may be used to guide screening strategies,” they said.