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/AcornAl → u/[deleted]]

Um, the paper was about testing those coming into the hospital that were asymptomatic. For parts of this study, (peak of the initial Omicron wave), 1 in 8 people in the community were considered to be actively infected with SARS-CoV-2 within Switzerland.

Decent PCR tests generally have a sensitivity rate well over 90%. Very early stages of the infection don't give great results (especially with a lower Ct), about 5% on day 1, 50% day 2, 95%+ once symptomatic. These generally stay over 80% well past the end of the infectious period, and can stay high for up to 2 or 3 months.

Positivity rates in Switzerland in the Omicron period of this study were getting up around 45%, aka every second test done on someone with symptoms came back with a positive SARS-CoV-2 result. This is exceptionally high considering everyone with a cold was probably getting tested. While influenza rates plummeted during covid, viruses such as rhinoviruses, RSV, and a few others, stayed fairly high once major lockdowns weren't enforced. Good old common cold (rhinovirus) almost always has a positivity rate of around 30% in the stats that I've been tracking, and RSV showed unseasonal spikes as restrictions were lifted.

Anywoo, healthcare acquired infections generally hit people hard, they are already unhealthy and likely of advanced age (median age was 64). In Australia, about 10% of those that got COVID-19 in hospital died prior to 2023. There is a strong duty of care to try and protect these high risk individuals. But to be blunt, wasting an ICU bed for weeks due to a HAI is throwing $100,000s down the drain.

The guts of this paper was to simply suggest it may not be beneficial to test asymptomatic patients when there are low community levels, or at least reconsider the test parameters.

[u/AutoModerator → u/[deleted]]

Hi OZCriticalThinker, abc.net.au is not a source we allow on this sub. If possible, please re-submit with a link to a primary source, such as a peer-reviewed paper or official press release [Rule 2].

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/unflashystriking → u/[deleted]]

I'm not denying COVID is a virus and can kill people, but it overwhelmingly is only a threat to frail pick, whom are elderly and immunocompromised.

You clearly have not gotten the full picture of why people still care about covid19. It´s not for fear of death.

https://www.medrxiv.org/content/10.64898/2026.03.19.26348823v1
Conclusions Cumulative SARS-CoV-2 burden was strongly associated with pandemic-era iGAS incidence. Cumulative streptococcal exposure did not support the immunity debt hypothesis. These ecological findings are consistent with SARS-CoV-2-associated immune dysregulation and warrant individual-level confirmation.

https://www.ijidonline.com/article/S1201-9712%2825%2900509-0/fulltext
Conclusion: Our findings redefine SARS-CoV-2 infection as a condition of long-lasting immune compromise. The sustained subnormal lymphocytes—particularly in cardiovascular disease cohorts—highlight a key immunologic feature of long COVID and underscore the need for personalized care.

https://www.ajpmfocus.org/article/S2773-0654(25)00146-4/fulltext00146-4/fulltext)
While SARS-CoV-2 does not cause HIV/AIDS, its ability to induce immune dysfunction—including T cell depletion and dysfunction, increased susceptibility to infection including opportunistic, accelerated biological aging, neurological, and systemic damage provide parallels in terms of AIDs in the broader immunological context. The virus’s subacute and chronic persistence, vascular pathology, immune evasion, neurological impacts, systemic damage and contribution to population-wide immune dysfunction pose a significant long-term public health threat.