Viral bacterial co-infection of the respiratory tract during early childhood

Abstract

Acute respiratory infection (ARI) is an important cause of morbidity in children. Mixed aetiology is frequent, with pathogenic viruses and bacteria co-detected in respiratory secretions. However, the clinical significance of these viral/bacterial co-infections has long been a controversial topic. While severe bacterial pneumonia following influenza infection has been well described, associations are less clear among infections caused by viruses that are more common in young children, such as respiratory syncytial virus. Although assessing the overall contribution of bacteria to disease severity is complicated by the presence of many confounding factors in clinical studies, understanding the role of viral/bacterial co-infections in defining the outcome of paediatric ARI will potentially reveal novel treatment and prevention strategies, improving patient outcomes. This review summarizes current evidence for the clinical significance of respiratory viral/bacterial co-infections in young children, discusses possible mechanisms of cooperative interaction between these pathogens and highlights areas that require further investigation.

Viral/bacterial respiratory tract co-infections in children

“…Evidence from previous studies suggests that RSV may trigger an outgrowth of S. pneumoniae from the URT flora through promotion of bacterial adherence and disruption of bacterial clearance mechanisms (128,138,140,262). However, we have previously hypothesised that, since RSV virion and S. pneumoniae complexes have been shown to form (128,136,137), these complexes may be co-transmitted in respiratory secretions, particularly in settings of rapid transmission such as childcare centres (6). Longitudinal studies with samples taken before, during and after an RSV infection within the same participant may represent the best way to differentiate between these hypotheses, however, to date such longitudinal studies have focused on characterising the nasopharyngeal microbiota, and have only shown increases in abundance of the Streptococcus genus during viral ARI, without species-level resolution and without reporting changes in abundances surrounding an ARI episode within individuals (5, 18).…”

“…Thus, there are concerns that in many paediatric ARI cases, antibiotic prescriptions are unjustified and potentially contribute to the development of antibiotic resistance (70). Specific antivirals have been developed for IAV and are used in severe cases requiring hospitalisation and 6 cases with increased risk of complications (e.g. children aged < 2 years); however, for the other important viral respiratory pathogens no antivirals are currently available.…”

“…pneumoniae, potentially resulting in positive selection pressures on pneumococcal strains that interact better with the virus, and thereby leading to strain-specific co-transmission and co-detection (6). Therefore, the main focus of this study was to investigate pathogen co-detection patterns between RSV and S. pneumoniae strains.…”

“…Viral/bacterial co-infections have also been reported (reviewed in Brealey et al (6)), particularly well characterised in secondary bacterial infections following influenza virus infection (7). However, outside of epidemics, influenza is a relatively infrequent pathogen of young children (8).…”

“…We (1) and others (56) have previously found increased co-detection of H. influenzae and S. pneumoniae with RSV in Brisbane-based cohorts of children with ARI, however neither of these studies investigated the effect of the co-detections on disease severity. While there is no reason to assume that these possible effects would be any less severe than those studied in other climates, due to the conflicting evidence concerning the relationship between viral and bacterial co-detections and disease severity, a number of studies from diverse populations are required to fully understand the complex interactions of potential pathogens in the respiratory tract and their effect on host disease (6). In this study, the respiratory viruses and bacteria present during viral ARI were further characterised in a cohort of young children aged less than two years presenting at the emergency department (ED) of a Brisbane children's hospital.…”