title: What is the seasonal distribution of community acquired pneumonia over time? A systematic review.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: School of Public Health and Human Biosciences, La Trobe University, Melbourne, Australia; Emergency & Trauma Centre, The Alfred Hospital, Melbourne, Australia.
authors: Katherine M
authors: KM
authors: Murdoch
authors: Emergency & Trauma Centre, The Alfred Hospital, Melbourne, Australia; Department of Epidemiology & Preventive Medicine, Monash University, Melbourne, Australia.
authors: Biswadev
authors: B
authors: Mitra
authors: Queensland Children's Medical Research Institute, The University of Queensland, and Children's Health Queensland, Queensland, Australia; Communicable Diseases Unit, Queensland Health, Australia.
authors: Stephen
authors: S
authors: Lambert
authors: School of Public Health and Human Biosciences, La Trobe University, Melbourne, Australia. Electronic address: b.erbas@latrobe.edu.au.
authors: Bircan
authors: B
authors: Erbas
mesh_terms: D017677:Age Distribution; D001315:Australia / Q000453:epidemiology; D017714:Community-Acquired Infections / Q000453:epidemiology; D004636:Emergency Service, Hospital / Q000639:trends*; D014943:Global Health / Q000639:trends; D006301:Health Services Needs and Demand / Q000639:trends; D006760:Hospitalization / Q000639:trends*; D006801:Humans; D015994:Incidence; D011014:Pneumonia / Q000453:epidemiology*; D012621:Seasons; D017678:Sex Distribution
keywords: Admissions; Community acquired; Pneumonia; Seasonality