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Volume 18
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10.3390/v18010040
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Article

Redesigning Isolation Practices: Evaluation of a Comprehensive Protocol for Respiratory Virus Control Including Cycle Threshold (Ct) Value Dynamics

by
Stefanie Lemmens
1,
Kevin Janssen
1,
Tine Nelis
2,
Ahmed Elmahy
3,
Noëlla Pierlet
3,
Els Oris
1 and
Deborah Steensels
1,4,*
1
Department of Molecular Microbiology, Ziekenhuis Oost-Limburg, 3600 Genk, Belgium
2
Department of Infection Prevention and Control, Ziekenhuis Oost-Limburg, 3600 Genk, Belgium
3
Central Data Coordination, Hospital Outbreak Support Team, Ziekenhuis Oost-Limburg, 3600 Genk, Belgium
4
Faculty of Medicine and Life Sciences—Biomed, University Hasselt, 3500 Hasselt, Belgium
*
Author to whom correspondence should be addressed.
Viruses 2026, 18(1), 40; https://doi.org/10.3390/v18010040
Submission received: 14 November 2025 / Revised: 16 December 2025 / Accepted: 19 December 2025 / Published: 25 December 2025
(This article belongs to the Section General Virology)
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Abstract

The recent literature has debunked the widespread hypothesis that viruses are primarily transmitted via droplets and not beyond 1.5 m, and transmission via contact has been downplayed. Hence, an evidence-based revision of the existing isolation guidelines for respiratory viruses was needed. Therefore, a completely new protocol for respiratory virus isolation in terms of personal protective equipment and patient room air purification was evaluated. Isolation relief criteria based on Ct values in follow-up sampling were assessed. A Ct value of <28 was employed as a proxy for potential active replication and associated transmissibility. Between 25% and 50% of patients who tested positive for RSV, HRV, hMPV, or SARS-CoV-2 continued to exhibit high viral loads on day 7 post-initial diagnosis, underscoring the potential for sustained infectivity. Hence, the discontinuation of isolation measures for these patients without follow-up testing may carry a considerable risk of ongoing viral transmission. On the contrary, only 7% of patients positive for Flu and 14% for PIV had a follow-up sample on day 7 with a Ct value of less than 28. Ct values increased more rapidly in influenza, indicating faster viral clearance compared to other respiratory viruses. Based on these results, the policy of a standard 7-day isolation period without follow-up testing could be adopted for influenza-positive patients.
Keywords: isolation practices; cycle threshold dynamics; SARS-CoV-2; non-SARS-CoV-2 viruses isolation practices; cycle threshold dynamics; SARS-CoV-2; non-SARS-CoV-2 viruses
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MDPI and ACS Style

Lemmens, S.; Janssen, K.; Nelis, T.; Elmahy, A.; Pierlet, N.; Oris, E.; Steensels, D. Redesigning Isolation Practices: Evaluation of a Comprehensive Protocol for Respiratory Virus Control Including Cycle Threshold (Ct) Value Dynamics. Viruses 2026, 18, 40. https://doi.org/10.3390/v18010040

AMA Style

Lemmens S, Janssen K, Nelis T, Elmahy A, Pierlet N, Oris E, Steensels D. Redesigning Isolation Practices: Evaluation of a Comprehensive Protocol for Respiratory Virus Control Including Cycle Threshold (Ct) Value Dynamics. Viruses. 2026; 18(1):40. https://doi.org/10.3390/v18010040

Chicago/Turabian Style

Lemmens, Stefanie, Kevin Janssen, Tine Nelis, Ahmed Elmahy, Noëlla Pierlet, Els Oris, and Deborah Steensels. 2026. "Redesigning Isolation Practices: Evaluation of a Comprehensive Protocol for Respiratory Virus Control Including Cycle Threshold (Ct) Value Dynamics" Viruses 18, no. 1: 40. https://doi.org/10.3390/v18010040

APA Style

Lemmens, S., Janssen, K., Nelis, T., Elmahy, A., Pierlet, N., Oris, E., & Steensels, D. (2026). Redesigning Isolation Practices: Evaluation of a Comprehensive Protocol for Respiratory Virus Control Including Cycle Threshold (Ct) Value Dynamics. Viruses, 18(1), 40. https://doi.org/10.3390/v18010040

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