Risks for frequent antimicrobial-treated infections in postmenopausal women

Background and aims: Infections are a major cause of morbidity and mortality in older adults. Little is known about factors that alter the susceptibility to infection in the older population. This study in postmenopausal women examines health-related conditions and behavioral factors that may increase the risk of frequent infections, defined as having, on average, one or more infections per year. Methods: A prospective cohort study with 5 years of follow-up was conducted in 1320 women aged 55 to 80 years. The subjects were Group Health Cooperative of Puget Sound (GHC) enrollees screened for a large fracture prevention trial who also participated in a survey of dietary and supplemental vitamin use. The main outcome, total number of infection events per subject, was derived from a new method of identifying outpatient infections based on the antimicrobial prescription fills recorded in GHC automated pharmacy records. Results: Prevalent lung disease (OR=6.1, 95% CI 2.8-13.4), receiving a prescription for vitamin C (OR=2.1, 95% CI 1.4-3.4), and the second and third tertiles of the Chronic Disease Score (OR=1.7, 95% CI 1.1-2.7 and OR=2.4, 95% CI 1.5-3.9, respectively) were associated with 5 or more antimicrobial-treated infections during follow-up. A body mass index (BMI) of less than 22 kg/m² (OR=0.6, 95% CI 0.3-1.0) was suggestive of an association. Conclusions: The study provides new information on risk factors for outpatient infections and raises new questions regarding the susceptibility to frequent infections in older women. In addition, the automated pharmacy record method used in this study offers a low-cost alternative for use in future epidemiologic research.