The changing epidemiology of community-acquired pneumonia: nationwide register-based study in Sweden.

BACKGROUND: There is limited evidence on the impact of pneumococcal conjugate vaccine childhood immunization programs (PCV-CIP) on community-acquired pneumonia (CAP) in individuals with underlying diseases.

METHODS: A nation-wide cohort study using Swedish health registers to assess the incidence of hospitalisation with all-cause (AC-CAP) and pneumococcal or lobar (PL-CAP) CAP between 2005-2015.

RESULTS: In total, 303,691 episodes of AC-CAP occurred, of which 14,225 were PL-CAP. Comparing before (2005-06) with after (2014-15) PCV-CIP, relative incidence reductions were 36% (95% Confidence Interval (CI) 32-40), 20% (CI 14-25), and 16% (11-22) of AC-CAP for age groups <2, 2-4, and 5-17 years respectively, with similar reductions in young children with and without co-morbidities. The reductions were more pronounced for PL-CAP. In the age groups 40-64, 65-74, 75-84, and >85 years there were relative increases of 11% (CI 8-14), 18% (15-22), 15% (CI 12-17), and 30% (CI 27-34) of AC-CAP respectively, but these increases were attenuated after adjustment for admittance practices. In adults with co-morbidities, there was an increase in incidence of AC-CAP, and PL-CAP, in contrast to adults without reported underlying diseases where the incidence was stable or diminished for some age groups. Over the study period there was an increased proportion of pneumonia patients with underlying diseases in all ages.

CONCLUSION: This emphasizes that direct preventive interventions should be targeted towards individuals with underlying diseases. Future studies should investigate reasons for the observed increased risk in adults with co-morbidities, e.g. due to pneumococcal non-vaccine serotypes, or other pathogens, preferentially affecting subjects with underlying diseases. This article is protected by copyright. All rights reserved.