Respiratory syncytial virus and influenza virus infection in adult primary care patients: Association of age with prevalence, diagnostic features and illness course

© 2020 The Author(s) Objectives: To better target new vaccines and treatments being developed for respiratory syncytial virus (RSV) and influenza virus (influenza), we studied the association of age with prevalence, diagnostic features and course of illness of these infections in primary care patients. Methods: Secondary analysis of observational data on the aetiology, diagnosis and prognosis in adults presenting to primary care with acute cough in 12 European countries (2007–2010) using regression analyses corrected for clustering of patients within countries. Age groups were 18–59 years, 60–74 years, and 75 years and older (75+). Results: Nasopharyngeal swabs for 144 (4.6%), 169 (5.4%) and 104 (3.4%) out of 3104 patients were polymerase chain reaction (PCR) positive for RSV, influenza A and influenza B, respectively. RSV prevalence in patients 75+ (8.5%) was twice the prevalence in those under 60 years (4.2%). Influenza prevalence was not associated with age. Diagnostic features for these viruses were not associated with age. Symptom duration was associated with age for RSV and influenza B, but not for influenza A. The odds of unresolved symptoms after 28 days were associated with age for RSV only. Illness deterioration was associated with age for RSV, with patients 75+ at increased risk, but not for influenza. Conclusion: In adults presenting to primary care with acute cough, the diagnostic features of RSV or influenza infection are not associated with age. For RSV both the prevalence and illness course are significantly worse at higher age, for influenza only the illness course is.