A new method for identifying antibiotic-treated infections using automated pharmacy records

For research purposes, there are few alternatives to costly surveillance for ascertaining infections in community populations. We propose a new approach based on antibiotic prescription fills in automated pharmacy records of the Group Health Cooperative of Puget Sound, in Seattle, Washington, to identify treated infections in postmenopausal women. After excluding probable antimicrobial prophylaxis and chronic antibiotic use, four intervals between antibiotic fills (30, 45, 60, and 90 days) were tested for their ability to detect new infections. Concordance with outpatient medical record reviews was evaluated in 150 women. The sensitivity of the automated pharmacy records using the four cutpoints for detecting new infections ranged from 88 to 80%, from 30 to 90 days, respectively. Of the 81 women with no infection in the chart reviews, 75% also had no infection using the pharmacy method. Good agreement was found between the two methods for counts of infections per person over the 2-year follow-up, with the 60-day cutpoint showing the greatest overall agreement with chart reviews (kappa = 0.55). The pharmacy method presented here offers a useful new approach for infection ascertainment for epidemiologic research.