Population-based study on incidence, risk factors, clinical complications and drug utilisation associated with influenza in the United Kingdom

This large population-based study using the UK-based General Practice Resea rch Database was conducted to quantify influenza-related physician visits, clinical complications of and risk factors for influenza, and related drug use in all age groups from 1991 to 1996. A total of 141,293 subjects who ha d one or more diagnoses of influenza or influenza-like illness during the s tudy period as well as the same number of age-, sex-, practice and calendar time-matched controls were identified. Adults aged 15-64 years had the hig hest influenza incidence rate, The risk of getting influenza was particular ly increased for subjects with chronic respiratory conditions (asthma or ch ronic obstructive pulmonary disease, odds ratio 1.65, 95% confidence interv al 1.60-1.70). Subjects with influenza were more likely to have a diagnosis of clinical complications than control subjects (relative risk 3.4, 95% co nfidence interval 3.3-3.6). The risk of developing clinical complications w as highest for children and was elevated for subjects with certain underlyi ng chronic conditions. In absolute terms, otherwise healthy adults (15-64 y ears) accounted for the greatest proportion of all influenza-related physic ian visits as well as clinical complications in this study population. Of t he 141,293 subjects with influenza, 83,911 (59.4%) received drugs on prescr iption. The most frequently prescribed drugs were antibiotics (45.2%), foll owed by antipyretics/analgesics (22.5%). Influenza patients were approximat ely six times more likely to use drugs on prescription than controls. This analysis may lead to further analyses on the economic impact of influenza a nd the contribution of different population groups to that burden.