Respiratory syncytial virus and Streptococcus pneumoniae: Partners in crime

Respiratory syncytial virus (RSV) and Streptococcus pneumoniae are major causes of acute respiratory infections worldwide, particularly in infants, young children, and older adults. Increasing attention has focused on interactions between them and their role in shaping clinical outcomes. This chapter examines the relationship between RSV and Streptococcus pneumoniae, reviewing epidemiological observations, proposed molecular and immunological mechanisms, and the clinical implications of co-infection. Epidemiological studies report temporal associations between RSV circulation and increased pneumococcal disease, including pneumonia and invasive pneumococcal disease. Experimental studies suggest several mechanisms underlying this interaction, including direct viral-bacterial binding, RSV-induced changes in respiratory epithelial cells that enhance pneumococcal adherence, and modulation of host immune responses that impair antibacterial defenses. These processes may increase pneumococcal virulence, promote bacterial colonization, and amplify inflammatory responses, potentially contributing to more severe clinical outcomes during co-infection. However, evidence also indicates that RSV-pneumococcal interactions can be complex and context-dependent, with some models demonstrating antagonistic effects such as accelerated viral clearance during pneumococcal colonization. Strain-specific pneumococcal factors and the timing of infection may further influence these dynamics. Further understanding the interplay between RSV and S. pneumoniae is important for interpreting patterns of respiratory disease. Nevertheless, current evidence supports prevention strategies, as interventions targeting one pathogen may have indirect effects on the other, ultimately reducing disease burden and the impact of antibiotic-resistant S. pneumoniae.