Identification of new risk factors for pneumonia: population-based case-control study

Background Certain conditions are established as risk factors for community-acquired pneumonia. There are a number of other conditions that may also be risk factors, but information on these is limited. Aim To determine new independent risk factors for community-acquired pneumonia using a very large primary care database. Design of study Nested case-control study. Setting Four hundred and forty-three general practices in the UK contributing to the QRESEARCH database. Method A total of 17 172 incident cases of all ages diagnosed with pneumonia between 1996 and 2005 were matched with up to five controls by age, sex, general practice, and calendar year. Associations between pneumonia and each established condition and potential risk factors were determined with odds ratios (ORs), using multiple conditional logistic regression analysis adjusted for smoking, socioeconomic status, and use of influenza and pneumococcal vaccines. Results The analysis confirmed the higher risk of pneumonia among patients with at least one of the established risk factors; the adjusted OR was 2.29 (95% confidence interval [CI] = 2.20 to 2.39). In addition, patients with the following conditions had a higher risk of pneumonia despite adjustment for known risk factors and confounders: stroke or transient ischaemic attack, rheumatoid arthritis, Parkinson's disease, cancers, multiple sclerosis, dementia, and osteoporosis. The adjusted OR for pneumonia among patients without an established risk factor but with at least one of the new conditions was 2.44 (95% CI = 2.24 to 2.65). Conclusion As well as confirming some established risk factors, this study has determined seven new independent risk factors for community-acquired pneumonia.