Chlamydia (Genital Infections) 2002
*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2002
In 2002, the Indiana State Department of Health (ISDH) received 17,299 reports of patients testing positive for Chlamydia trachomatis, the causative agent of chlamydia. Of all the reportable diseases in Indiana, chlamydia is the most commonly reported. The number of reported cases in 2002 exceeded that of any previous year (Figure 1).
In 2002, the incidence rate of chlamydia was 281 cases per 100,000 population, a 12 percent increase from 2001 (251.5). This increasing trend reflects endemic chlamydia in the presence of improved ascertainment of cases through time. Increasingly economical and sensitive diagnostic methods were employed through the late 1990s. Additionally, ISDH-funded screening sites have been added in recent years, resulting in more testing among young women. Steadily increasing incidence, therefore, does not necessarily reflect increasing propagation of this pathogen among Hoosiers. Rather, sensitivity of the surveillance system is increasing in response to expanded screening of those at risk.
Women are overrepresented among those diagnosed with chlamydia. Known female infections (13,341) exceeded those among males (3,850) by over three-fold. Chlamydia screening programs preferentially test females, because untreated infections cause reproductive sequelae. Pelvic inflammatory disease, a substantial proportion of which is caused by infection with C. trachomatis, is the primary cause of preventable infertility. Federally funded efforts of the Indiana Sexually Transmitted Disease (STD) Program and the Indiana Family Health Council resulted in selective screening of at-risk young women. Further, male chlamydia infections are often diagnosed as non-gonococcal urethritis, which is not reportable. Because these men do not receive pathogen-specific testing, chlamydia morbidity among males is understated. Therefore, the difference between genders reflects a difference in screening practices rather than greater prevalence among females.
Consistent with previous years’ distribution by age, the preponderance of cases was among adolescents and young adults (Figure 2). In 2002, over 89 percent of reported cases were among those 10-29 years of age. The age-specific rate for those 10-19 years of age was 707 per 100,000, while the rate among those 20-29 years of age was 1046 per 100,000.
The four counties with the greatest number of reported cases were Marion (6,673), Lake (1,687), Allen (1,308), and St. Joseph (1,132). Adjusting for population size, Marion County had the highest incidence rate (773.7), followed by St. Joseph County (425.6), Allen County (387.5), and Vanderburgh County (356.3). Figure 3 shows Indiana counties with five or more reported cases of chlamydia.
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