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Respiratory syncytial virus and other possible non-viral variables may contribute to the clinical severity of bronchiolitis in hospitalized infants. 

Respiratory syncytial virus (RSV) is an enveloped RNA virus that is primarily responsible for causing acute bronchiolitis. This viral infection leads to inflammation, characterized by swelling, excessive mucus production, and damage to the epithelial cells. Infants often require hospitalization due to the severity of the condition. The extent to which RSV load contributes to the risk factors associated with this pathogen remains a subject of debate and controversy.

In a recent study published in the journal Pathogens, researchers investigated the association between RSV load, the kinetics of viral replication, and the clinical course of RSV bronchiolitis in hospitalized infants to determine the role of RSV load in the severity of the disease. 

Study Design and Characteristics

A total of 38 infants diagnosed with RSV bronchiolitis were included in the hospital-based study. The average age of these infants upon admission was 3.9 months, with an average weight of 5.9 kg. The study followed a prospective approach, collecting nasopharyngeal aspirates every 48 hours and evaluating the dynamics of RSV load and clinical indicators associated with the severity of bronchiolitis.

RSV Load and Viral Replication Kinetics Analysis During Hospitalization

Regardless of the clinical history of bronchiolitis, virus replication peaks within the first 48 hours of admission and significantly declines over the subsequent periods (p < 0.0001). Based on the length of hospitalization, a median of three nasopharyngeal aspirates were obtained and assessed for each case. Peak RSV loads were found in 68.4% of patients upon admission and in 31.6% of cases after 48 hours. 

Need for Oxygen Related to High RSV Load

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When RSV load was tested at different periods, significantly higher RSV-RNA levels at admission were connected to the requirement for oxygen treatment (p = 0.03), in particular, the use of high-flow nasal cannulae (p = 0.04), and a more extended period of oxygen therapy (p = 0.04). There were no notable differences in the need, type, and duration of oxygen treatment based on the RSV load discovered at subsequent time points after admission. 

Effect of RSV Load on Baseline and Non-Viral Markers

Lower white blood cell counts (p = 0.03), particularly lymphocyte counts (p = 0.04), and C-reactive protein levels (p = 0.01), as well as younger patients (p = 0.02), were all associated with greater RSV-load values. Younger patients’ hospital stays were considerably longer when non-viral risk variables were considered (p = 0.03). These findings indicate a diminished capacity to regulate viral replication.


Piccirilli, G., Rocca, A., Borgatti, E. C., Gabrielli, L., Zama, D., Pierantoni, L., Leone, M., Totaro, C., Pavoni, M., Lazzarotto, T., & Lanari, M. (2023). Respiratory Syncytial Virus-Load Kinetics and Clinical Course of Acute Bronchiolitis in Hospitalized Infants: Interim Results and Review of the Literature. Pathogens, 12(5), 645. https://doi.org/10.3390/pathogens12050645