Impact of the 2009 influenza A H1N1 pandemic on invasive pneumococcal disease in adults

Background: The incidence of invasive pneumococcal disease (IPD) appears to be associated with influenza. The objectives of this study were to evaluate the changes in IPD incidence and clinical data as well as the trends in Streptococcus pneumoniae serotype distribution in adults during the peak period of the 2009 influenza A H1N1 pandemic (IAP). Methods: We performed a prospective multicentre study on IPD from week 42 to 48, 2009 in an area of Barcelona (Catalonia, Spain) covering 1,483,781 adult inhabitants. Serotyping was done by Quellung reaction. The data from 2009 were compared to those from the same periods in 2008 and 2010. Results: Two hundred and three cases of IPD were detected during 2009, compared with 182 in 2008 and 139 in 2010. The incidence of IPD during the 7-week study period in 2009 (2.89) was statistically higher than that observed in 2008 (1.96) and 2010 (1.46). IAP was confirmed in 3/30 patients during the 2009 study period. Patients with IPD in 2009 were significantly healthier and younger than those in the other years, although the mortality was higher than in 2008 (p = 0.05) and 2010 (p > 0.05). Eleven (10 non-PCV-7) serotypes not present in 2008 appeared in 2009. Conclusions: During weeks 42 to 48, in which the 2009 IAP peaked in Catalonia, the incidence of IPD was statistically higher than that observed in the same time period in 2008 and 2010, with some differences in the epidemiological data, showing a close relationship between S. pneumoniae and influenza.