# Unmasking Viral Causes of Hospitalized Respiratory Infection: Five Years of Respiratory Virus Surveillance in Vietnam by Multiplex Real-Time PCR Assay

## TL;DR

This study analyzed respiratory viruses in hospitalized patients in Vietnam over five years, showing the value of a multiplex PCR test in identifying common and emerging viral causes of severe infections.

## Contribution

The study provides a comprehensive five-year analysis of respiratory virus detection rates in hospitalized patients using a multiplex real-time PCR assay in Vietnam.

## Key findings

- The overall respiratory virus detection rate was 31.88%, with higher rates in children than adults.
- Rhinovirus, influenza A, RSV, and parainfluenza virus type 3 were the most frequently detected viruses.
- SARS-CoV-2 dominated during the 2021 pandemic peak, while measles re-emerged in 2024, mainly in children.

## Abstract

Aim of the study: To investigate the detection rate of respiratory viruses identified by multiplex real-time PCR (MPL real-time PCR) in respiratory specimens collected from hospitalized patients with acute lower respiratory tract infections (LRTI) over a five-year period (2020–2024), and to emphasize the importance of MPL real-time PCR testing in identifying respiratory viruses responsible for severe lower respiratory tract infections requiring hospitalization. Subjects and Methods: This cross-sectional retrospective study analyzed 15,936 respiratory specimens collected from hospitalized patients between 2020 and 2024. Seventeen respiratory viruses were detected using MPL real-time PCR. Statistical comparisons were performed using the chi-square test. Results and Discussion: The overall respiratory virus detection rate was 31.88% and was significantly higher in children than in adults (52.98% vs. 18.10%). The most frequently detected viruses were rhinovirus, influenza A, respiratory syncytial virus, and parainfluenza virus type 3, while influenza A and SARS-CoV-2 predominated in adults. During the peak of the COVID-19 pandemic in 2021, SARS-CoV-2 accounted for 78.92% of detected viruses, accompanied by marked suppression of other respiratory pathogens. Measles virus re-emerged in 2024, predominantly affecting children (17.65%). Most Respiratory virus-positive cases (82.8%) involved single-agent infections. Conclusions: Hospitalized acute LRTI cases often lack distinctive clinical signs to identify viral pathogens. MPL real-time PCR provides simultaneous multi-virus detection, enabling accurate etiological diagnosis and strengthening hospital-based viral surveillance, particularly in resource-limited settings.