RSV-bacterial co-infection is associated with increased illness severity in hospitalized children - Results from a prospective sentinel surveillance study

Abstract

Purpose: During the autumn/winter respiratory syncytial virus (RSV) epidemics, bacterial co-infection is common and affects the severity of the disease. We aimed to understand the relationship between RSV-bacterial co-infections and clinical severity since the change of RSV seasonality after the COVID-19 pandemic. Methods: We conducted a prospective, sentinel surveillance study at 20 sites in Portugal in children under two years old hospitalized with RSV, between April 2021 and January 2023. The effect of co-infection with potentially pathogenic bacteria (PPB) on the length of hospitalization and disease severity (defined by the need for ventilation or admission to an intensive care unit-ICU) was investigated using multivariate linear and log-binomial regression models. Age group (<6 months/≥6 months) and prematurity (yes/no) were included in models as potential confounders. Results: We report two RSV off-season epidemics: June 2021-February 2022 and May-October 2022. Among 678 RSV hospitalizations, 67.4 % occurred in children under 6 months old and 15.3 % in pre-term; 20.4 % tested positive for PPB; median length of hospitalization was five days (IQR: 3-7days); 5.8 % had at least one underlying condition. The most common bacteria were Haemophilus influenzae and Streptococcus pneumoniae. Children co-infected with PPB had a higher rate of ICU admission (29.7 % versus 3.5 %, p<0.001), resulting in more prolonged hospitalizations (median of 7 days versus 5 days, p<0.001) and a 13-fold risk of having severe disease (RR: 13.2, 95 CI: 7.3-23.9). Conclusion: RSV-bacterial co-infection was associated with increased length of hospitalization and severe illness during off-season epidemics. This risk is probably overestimated, as laboratory testing for bacterial infections is usually higher in severely ill-appearing children. Measures to prevent outgrowth of pathogenic bacteria within the respiratory tract should be discussed.