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

## TL;DR

This study evaluates a new isolation protocol for respiratory viruses, showing that some viruses require longer isolation due to sustained infectivity.

## Contribution

The study introduces a protocol using Ct values to guide isolation decisions for respiratory viruses.

## Key findings

- 25-50% of RSV, HRV, hMPV, and SARS-CoV-2 patients had high viral loads on day 7, indicating ongoing infectivity.
- Flu and PIV patients showed faster viral clearance, with only 7% and 14% having Ct values <28 on day 7.
- A 7-day isolation without testing may be sufficient for influenza patients.

## 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.