Wastewater Surveillance Supports COVID-19 Screening in Hospitals

A high viral incidence of SARS-CoV-2 detected in wastewater was found to correlate with increased rates of positive COVID-19 test results within surrounding communities, reinforcing the value of preventive screening—even among asymptomatic patients.¹

These findings, published in JAMA Network Open, highlight the potential role of wastewater surveillance as a real-time epidemiologic tool to guide hospital screening strategies. Although COVID-19 case counts have declined in recent months, the disease remains a persistent global public health concern, particularly as emerging variants continue to challenge existing prevention and treatment approaches.^2,3 The study specifically evaluated whether universal screening of asymptomatic patients in hospital settings could help reduce transmission, particularly during periods of elevated community spread.¹

Researchers conducted a retrospective quality-control cohort study between January 2024 and February 2025 at the University Hospital Basel in Switzerland. Community viral incidence was estimated using wastewater data collected from the sewage system in Basel-Stadt, where monitoring programs have been in place since July 2021. Wastewater surveillance has emerged as a valuable proxy for tracking population-level infection trends, often identifying viral surges earlier than clinical testing alone.

The study included 78,511 saliva samples collected from 44,095 patients. After excluding tests due to missing cycle threshold (Ct) values, sampling errors, and ineligible demographics, a total of 75,667 polymerase chain reaction (PCR) tests from 42,666 patients were analyzed. The median patient age was 64 years, and 50.6% were female.

Screening frequency varied throughout the study period. Patients were initially tested at 7-day intervals over 5 weeks, followed by a 5-day interval for 47 weeks and a 3- to 5-day interval for an additional 37 weeks. Most tests (approximately 59%) were conducted within the first 72 hours of hospital admission, while 40.8% of follow-up tests occurred later during hospitalization.

Overall, the positivity rate was relatively low, at 1.2% (899 positive tests among 761 patients). Of these cases, 63.5% were classified as true positives, while 36.5% were considered false positives. Importantly, the correlation between test positivity, local 7-day incidence rates, and wastewater viral load was stronger for admission screenings than for follow-up testing, suggesting that community transmission trends are particularly relevant at the point of hospital entry.

The study also found that test accuracy varied depending on community infection levels. During periods of high community incidence, the false-positive rate dropped to 35.1%, compared with 55.8% during low-incidence periods. This finding underscores the importance of aligning screening strategies with real-time epidemiologic data.

“Our findings align with prior research suggesting that universal SARS-CoV-2 screening in health care settings can help identify asymptomatic carriers, thereby preventing nosocomial transmission during periods of high community 7-day incidence,” the study authors wrote.

However, the researchers emphasized that universal screening is not without trade-offs. False-positive results can lead to unnecessary isolation, delayed care, and increased strain on hospital resources. The study’s limitations—including its single-center design, retrospective methodology, and variability in testing intervals—may also affect the generalizability of the findings. Additionally, incomplete confirmatory testing and gaps in wastewater data could introduce inconsistencies in interpretation.

“Our findings highlight the considerable unintended outcomes associated with false-positive results, which can strain health care systems and adversely affect patient outcomes,” the authors concluded. “These results emphasize the importance of context-driven implementation, in which screening efforts are aligned with epidemiological trends and resource availability.”

Taken together, the findings suggest that while universal screening of asymptomatic patients can be a valuable tool during periods of high community transmission, its effectiveness depends on thoughtful integration with surveillance data. Wastewater monitoring, in particular, may offer a scalable and timely method to inform when such screening strategies are most beneficial.

References

1. Weiss M, Urwyler P, von Rotz M, et al. Diagnostic value and outcomes of systematic SARS-CoV-2 screening in asymptomatic patients. JAMA Netw Open. 2026;9(4):e265867. doi:10.1001/jamanetworkopen.2026.5867
2. Hille K. What should you know about the COVID cicada variant? Seattle Times. April 7, 2026. Accessed April 28, 2026. https://www.seattletimes.com/seattle-news/health/what-should-you-know-about-the-covid-cicada-variant/
3. Covid-19 cases | WHO COVID-19 Dashboard. World Health Organization. March 28, 2026. Accessed April 28, 2026. https://data.who.int/dashboards/covid19/cases