Pneumonia and influenza, and respiratory and circulatory hospital admissions in Belgium: a retrospective database study

BACKGROUND: Influenza infections can lead to viral pneumonia, upper respiratory tract infection or facilitate co-infection by other pathogens. Influenza is associated with the exacerbation of chronic conditions like diabetes and cardiovascular disease and consequently, these result in acute hospitalizations. This study estimated the number, proportions and costs from a payer perspective of hospital admissions related to severe acute respiratory infections. METHODS: We analyzed retrospectively, a database of all acute inpatient stays from a non-random sample of eleven hospitals using the Belgian Minimal Hospital Summary Data. Codes from the International Classification of Diseases, Ninth Revision, Clinical Modification was used to identify and diagnose cases of pneumonia and influenza (PI), respiratory and circulatory (RC), and the related complications. RESULTS: During 2002-2007, we estimated relative hospital admission rates of 1.69% (20960/1237517) and 21.79% (269634/1237517) due to primary PI and RC, respectively. The highest numbers of hospital admissions with primary diagnosis as PI were reported for the elderly patient group (n = 10184) followed by for children below five years of age (n = 3451). Of the total primary PI and RC hospital admissions, 56.14% (11768/20960) and 63.48% (171172/269634) of cases had at least one possible influenza-related complication with the highest incidence of complications reported for the elderly patient group. Overall mortality rate in patients with PI and RC were 9.25% (1938/20960) and 5.51% (14859/269634), respectively. Average lengths of hospital stay for PI was 11.6 ± 12.3 days whereas for RC it was 9.1 ± 12.7 days. Annual average costs were 20.2 and 274.6 million Euros for PI and RC hospitalizations. Average cost per hospitalization for PI and RC were 5779 and 6111 Euros (2007), respectively. These costs increased with the presence of complications (PI: 7159, RC: 7549 Euros). CONCLUSION: The clinical and economic burden of primary influenza hospitalizations in Belgium is substantial. The elderly patient group together with children aged