What is the seasonal distribution of community acquired pneumonia over time? A systematic review

Abstract

Community-acquired pneumonia (CAP) is a growing public health concern in many developed countries including Australia. CAP account for an estimated two percent of all overnight hospital admissions in Australia. Despite the significant burden on the Australian healthcare system and the high level of morbidity and mortality associated with CAP, there has been a paucity of research on the incidence of disease in this country, particularly in relation to seasonal variation of emergency department presentations and subsequent admission. The following search terms were used: community-acquired AND pneumonia AND/OR seasonal AND season AND/OR variation OR differences. The limits used for the search terms included: "All Adult"; the years 1948 to current or 1948 to week 1 May 2012, (depending on the database); English language; and with full text. The databases searched included MEDLINE, Embase and CINAHL. Distinct seasonal patterns in the occurrence of CAP were observed: 34% of CAP admissions occurred in spring; 18% in autumn; 26% in winter; and 22% in summer (p=0.036). Hospital admissions for CAP were significantly higher in the winter and spring (p=<0.001) and highest in December (20.5%) and January (25.1%). Peak hospitalisations from January through to April were observed. The included studies were conducted in the northern hemisphere where the months December to February relate to winter. International studies have shown an association between seasonal variation and the occurrence of CAP in temperate and subtropical climates. Selected studies had methodological limitations that limit conclusions and applicability to clinical practice. There are no studies in the Australian context. Further epidemiological studies are required to elucidate this important aspect of the epidemiology of CAP.