| The Centers for Disease Control and Prevention (CDC) estimates between 3-4 million Chlamydia trachomatis genital infections occur each year, making it the most commonly reported sexually transmitted disease (STD) in the United States. Despite its frequency, little is known about the parameters that govern its transmission, including the average duration of infectiousness, the per-partner transmission efficiency, or the basic or effective reproductive numbers (R0 and R, respectively).;In the first study, a general method was developed to estimate the duration of infectiousness among individuals infected with C. trachomatis infections in an inner-city population of persons aged 14-24 years. Prevalence and recall data were combined with a susceptible-infectious-susceptible compartmental model and the exponential survival equation to estimate the duration of infectiousness and to compare these estimates between females and males. Duration of infectiousness was estimated to be 6.4 months, and did not vary between females (6.5 months) and males (6.2 months; recovery rate ratio = 0.95, 95% confidence interval (CI): 0.61, 1.5), in contrast to several previous studies. There was some evidence that study site was an effect measure modifier. In Boston, MA, the recovery rate ratio = 0.67, 95% Cl: 0.3, 2; in Indianapolis, IN, the recovery rate ratio = 1.0, 95% CI: 0.6, 1.8.;In the second study, the basic and effective reproductive numbers and 95% simulation intervals (SI) were estimated among cases in a cross-sectional study. The basic reproductive number (R0) describes the epidemic potential of a pathogen when a small number of cases are introduced into a population where most individuals are susceptible. The effective reproductive number (R) describes transmission when a pathogen has already established itself. In this study, R0 = 1.0, 95% SI: 0.7, 1.6. Thus, on average, each infectious host spread C. trachomatis to one sex partner while infectious. However, given a prevalence of 44%, C. trachomatis already has a foothold in the study population. The effective reproductive number, R, was therefore appropriate to describe the epidemic potential of C. trachomatis: R = 0.56, 95% SI: 0.41, 0.87. This indicated that fewer than one susceptible individual was infected by each infectious host. The elevated prevalence in the study population may dampen or may have dampened the potential for an epidemic to occur. Despite substantial heterogeneity in the contact rate, the assumption of random mixing was met: prevalence was nearly equal in all quintiles of the average weighted contact rate. Though counterintuitive, reducing the number of partners per unit time, a common strategy in STD prevention, may not result in a subsequent decrease in prevalence without first initiating a mass screening and treatment campaign.;In study three, the relation between age (10-19 years vs. 20 years and over) at the first reported C. trachomatis infection and the hazard of repeat infection was examined using routinely collected STD data from the Chicago Department of Public Health. Those aged 10-19 years at the initial report were 2.26 times more likely to have a repeat infection over follow-up than those aged 20 years and older. When five-year age strata were examined, there was an inverse association between age and the hazard of repeat infection. Those aged 10-14 years were almost 7 times more likely to have a repeat C. trachomatis infection over follow-up than those aged 35 years and older (hazard ratio = 6.9, 95% CI = 6.3, 7.5).;These three studies have brought together aspects of transmission dynamics and epidemiologic methods in order to provide estimates of key transmission parameters that influence the spread of C. trachomatis. , Though often difficult to estimate, obtaining valid and precise estimates of these parameters is critical in order to evaluate current practices and to develop new strategies to halt the spread of STDs, generally, and C. trachomatis, in particular. |
