Isolation of hospitalized patients with influenza and COVID-19 is disproportionate to measurable contagiousness

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OBJECTIVES: Outbreaks of respiratory viruses, such as influenza and SARS-CoV-2, place significant strain on healthcare systems. Although isolation can reduce virus transmission, it also incurs economic and psychological costs, including higher mortality rates due to reduced provider interaction. RT-PCR is highly sensitive for the detection of viruses but typically yields positive results after patients are no longer contagious. This has primarily led to reliance on clinical symptoms for decisions regarding cessation of isolation. METHODS: Here, we assessed the contagiousness of hospitalized patients infected with Influenza A or SARS-CoV-2 using high-sensitive viral culturing of oropharyngeal swap samples, with the aim to evaluate whether patients are correctly isolated in a Danish hospital during admission. Additionally, we compared the Ct values with the corresponding isolation outcome and assessed the quality of the samples by RT-PCR for the human housekeeping gene RNase P. RESULTS: A total of 47 patients were included in the study. As assessed by viral culture, 24 patients (51%) were not contagious by admission and for 26 patients (55%) isolation could have been discontinued earlier. By applying a Ct value of <33 as a proxy for contagiousness instead of current isolation criteria, we found that for influenza A the sensitivity could be improved significantly from 71.4% to 92.9% and the specificity from 53.6% 84.3%, corresponding to a potential reduction of isolation days of 40%. DISCUSSION: Our findings indicate significant over isolation practice and thus emphasize the need for assays enabling a better estimation of contagiousness. We found that the PCR Ct value holds significant potential for increasing isolation precision, but this requires a dedicated effort from assay manufacturers and clinical microbiologists to validate data and ultimately translate it into widely applicable PCR solutions.

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