Bacterial carriage and respiratory tract infections in subjects ≥ 60 years during an influenza season: Implications for the epidemiology of Community Acquired Pneumonia and influenza vaccine effectiveness

Introduction. During the 2010/11 influenza season an epidemiological prospective cohort active study was organized, to evaluate etiologic role due to the main bacteria and viruses causing Community Acquired Pneumonia (CAP) and Influenza like-illness (ILI) in elderly and to explore the role of the bacterial nose-pharingeal carriage in subjects with respiratory tract infections. Methods. An integrated active surveillance of a cohort of adults aged ≥ 60 y based on a double prospective and retrospective mechanisms of capture of ILI and CAP cases was organized. Samples were collected from all ILI and CAP prospectively identified. The samples were be tested by multiplex PCR for detection of the main respiratory bacteria and viruses. Results and discussion. The study population amounted to 2,551 adults. During the 2010/11 influenza season, the ILI cumulative incidence was 4.2%, that was twice higher than that calculated by regional sentinel-based Influenza surveillance system during the 2010/11 season in the elderly (2.2%). Among 45 patients with ILI of which had been collected the swab, 17 (37.8%) were positive for influenza viruses and 2 (4.4%) for RSV, 6 (13.3%) patients carried Streptococcus pn and 6 (13.3%) Haemophilus in. In the same period, 7 CAP cases were observed; 3 cases were prospectively identified and samples were collected, while 4 cases were retrospectively detected. The CAP cumulative incidence was 0,3%. The influenza vaccine effectiveness in prevention of laboratory-confirmed influenza emerged by our study was 61%, in condition of good antigenic matching between vaccine and circulating strains observed during the 2010/11. These data contribute to better defining the epidemiological picture of upper and lower respiratory tract infections, fundamental information in light of the recent introduction of new vaccines for prevention of pneumonia in the elderly, including 13-valent conjugate pneumococcal vaccine.