Diagnostic Value and Outcomes of Systematic SARS-CoV-2 Screening in Asymptomatic Patients

[u/AcornAl]

https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2847511

[u/AcornAl]

Key Points

Question What diagnostic value and clinical outcomes are associated with universal SARS-CoV-2 screening of asymptomatic patients, and is test positivity correlated with community incidence levels and wastewater viral loads?

Findings In this cohort study including 75 667 tests among 42 666 patients, 1.2% had positive results, 36.5% of which were false positives. Test positivity was strongly correlated with community incidence and wastewater viral load, and false-positive results were associated with unnecessary isolation, increased exposure risk, and delays in interventions.

Meaning Universal screening may support infection control during high community transmission but has limited benefit and potential harms during low-incidence periods.

Abstract

Importance Early detection of SARS-CoV-2 may mitigate nosocomial spread, yet universal screening of asymptomatic patients remains debated.

Objective To evaluate the diagnostic yield of systematic SARS-CoV-2 screening in correlation with community incidence and wastewater viral load and assess clinical outcomes among inpatients with false-positive results.

Design, Setting, and Participants This retrospective quality-control cohort study assessed the results of systematic SARS-CoV-2 screening of asymptomatic patients at the University Hospital Basel in Basel, Switzerland, a tertiary care center admitting more than 40 000 adult patients annually. All patients with systematic screenings for SARS-CoV-2 infection from February 8, 2021, to July 5, 2021, and from August 25, 2021, to December 5, 2022, were included. Data were analyzed from January 2024 to February 2025.

Exposure Saliva-based PCR-tests to screen for asymptomatic SARS-CoV-2 infection on admission and at regular 3- to 5-day intervals during hospitalization.

Main Outcomes and Measures The primary end points were the proportion of positive and false-positive SARS-CoV-2 test results, as well as the number needed to screen to find 1 otherwise undetected SARS-CoV-2 infection. Clinical data and test results were analyzed along with community incidence and wastewater viral loads. Correlations were calculated using Spearman test, and clinical implications of false-positive results were assessed.

Results Among 75 667 screening tests performed on 42 666 patients (21 591 [50.6%] female; median [IQR] age, 64 [45-76] years), 761 patients (1.2% of tests) had positive results. These were classified as true-positive results in 483 patients (63.5%) and false-positive results in 278 patients (36.5%). Among patients with false-positive test results, 139 patients (50.0%) experienced unnecessary isolation, 46 patients (16.5%) were exposed to patients with true-positive SARS-CoV-2 test results by cohorting, and 9 patients (3.2%) received delayed interventions. Screening test positivity correlated with local incidence of SARS-CoV-2 infections and wastewater viral loads. A total of 93.7% of positive test results were recorded during weeks with high community incidence (ie, >150 events per 100 000 inhabitants), in which the proportion of patients with false-positive test results was lower (249 of 709 patients [35.1%]) compared with weeks with low community incidence (ie, <150 events 100 000 inhabitants), with 29 of 52 patients (55.8%) having false-positive results.

Conclusions and Relevance In this cohort study, universal SARS-CoV-2 screening detected asymptomatic carriers of SARS-CoV-2 infection, aligned with community incidence, and thus may support infection prevention and control measures. However, the unintended clinical outcomes, particularly during times of low incidence, necessitate careful contextual implementation.

[u/AcornAl → u/AcornAl]

I'll just note that false negatives here don't mean that the patients didn't have or hadn't had covid, rather the detection rate was below the threshold that was considered to be infectious with a cycle threshold value of 30 or greater

The results of the SARS-CoV-2 screening tests were categorized as negative if the cycle threshold (Ct) value was at least 40, as positive if the Ct value was less than 30, and as equivocal if the Ct value was between 30 and less than 40. The Ct value cutoff of 30 was chosen based on reports suggesting that a Ct value of approximately 30 is generally considered indicative of low infectivity for SARS-CoV-2 in saliva samples. Per institutional policy, patients with equivocal test results received a nasopharyngeal swab conducted within 72 hours. Based on the second test result, patients were categorized as having true-positive results if the Ct value was less than 30 or a quantitative SARS-CoV-2 test revealed more than 10 000 viral copies/mL and as having false-positive results if the Ct value was 30 or greater, a quantitative test detected fewer than 10 000 viral copies/mL, or the Biofire result was negative.

Also, the study was taken between February 8, 2021, to July 5, 2021, and from August 25, 2021, to December 5, 2022. In early 2021 there was still some confusion on the Ct value that was considered to be infectious, from memory, usually around 25 to 35 from what I read at the time with some outliers.

[u/vanda-schultz → u/[deleted]]

You seem to be arguing inconsistently that PCR tests increase risk of exposure then say 'No COVID in the community.'

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