Sexual network structure as an indicator of epidemic phase.

Ascertaining epidemic phase for a sexually transmitted disease (STD) has depended on secular trend data which often contain significant artefacts. The usefulness of sexual network structure as an indicator of STD epidemic phase is explored in an analysis of community wide genital chlamydia reports, with network analysis of interviewed cases and linked sexual partners, in Colorado Springs, USA, 1996 to 1999. In this period, the chlamydia case rate per 100,000 increased by 46%. Three quarters of cases (n=4953) were interviewed, nominating 7365 partners; these, combined with index cases, made up the 9114 persons in the network. Epidemiologic analysis of cases suggests that secular trend increases are artefactual. Network analysis supports this view: overall network structure is fragmented and dendritic, notably lacking the cyclic (closed loops) structures associated with network cohesion and thus with efficient STD transmission. Comparison of network structure with that of an intense STD outbreak (characterised by numerous cyclic structures) suggests low level or declining endemic rather than epidemic chlamydia transmission during the study interval. These observations accord with intuitive and stochastic predictions.

Chlamydia transmission: concurrency, reproduction number, and the epidemic trajectory.

To identify factors that influence individual and group transmission of Chlamydia, the authors conducted community-wide contact tracing of chlamydia cases in Colorado Springs, Colorado, from mid-1996 to mid-1997. Case patients identified persons with whom they had had contact during the 6 months preceding diagnosis; contacts were actively sought and offered DNA amplification testing. Sexual contact networks were used to identify "source cases" and "spread cases," permitting estimation of the basic reproduction number (R0) for individuals and groups. Network and epidemiologic factors influencing R0 were assessed using univariate and multivariate procedures. Of 1,309 case patients, 1,131 (86%) were interviewed, and 2,409 contacts were identified. The 1,131 interviewed cases yielded 623.9 computed spread cases, for an overall R0 of 0.55. Few subgroups analyzed yielded a mean R0 exceeding unity-an observation in keeping with routine surveillance information which suggests that chlamydia incidence is declining in Colorado Springs. Concurrency, a network measure of simultaneous partnerships, was the most powerful predictor of transmission. Direct estimation of basic reproduction numbers for chlamydia using contact tracing techniques is feasible and can produce useful data with which to prioritize control efforts, evaluate interventions, and gauge the place of chlamydia on the epidemic continuum.

Establishing efficient partner notification periods for patients with chlamydia.

OBJECTIVES: To delineate chlamydia partner notification periods with high proportions of infected, untreated sexual partners, and to evaluate relevant Centers for Disease Control (CDC) recommendations. METHODS: Disease Intervention Specialists (DIS) offered contact tracing services to all chlamydia patients (N = 1,309) reported in Colorado Springs between July 1996 and June 1997. Patients were asked to identify sexual partners during the 180 days preceding treatment. Partners were actively sought by DIS and offered DNA amplification testing. RESULTS: Of 1,309 patients, 1,109 were interviewed, resulting in 2,293 named partners. Two fifths of eligible partners were located; inability to examine partners was related to time of last exposure and to frequency of sexual exposure. Of located partners, 95% were tested with DNA amplification technology. Adherence to CDC criteria identified 88% of infected, untreated partners; the other 12% consisted mainly of epidemiologically important asymptomatic men whose infection is seldom identified by current public health interventions. CONCLUSIONS: The chlamydia partner notification recommendations of the CDC are adequate, but miss men with long-standing infection. These men contribute to entrenched chlamydia endemicity; targeted programs to screen high-risk men merit serious consideration.