Comparability of Results from Pair and Classical Model Formulations for Different Sexually Transmitted Infections

The “classical model” for sexually transmitted infections treats partnerships as instantaneous events summarized by partner change rates, while individual-based and pair models explicitly account for time within partnerships and gaps between partnerships. We compared predictions from the classical and pair models over a range of partnership and gap combinations. While the former predicted similar or marginally higher prevalence at the shortest partnership lengths, the latter predicted self-sustaining transmission for gonorrhoea (GC) and Chlamydia (CT) over much broader partnership and gap combinations. Predictions on the critical level of condom use (Cc) required to prevent transmission also differed substantially when using the same parameters. When calibrated to give the same disease prevalence as the pair model by adjusting the infectious duration for GC and CT, and by adjusting transmission probabilities for HIV, the classical model then predicted much higher Cc values for GC and CT, while Cc predictions for HIV were fairly close. In conclusion, the two approaches give different predictions over potentially important combinations of partnership and gap lengths. Assuming that it is more correct to explicitly model partnerships and gaps, then pair or individual-based models may be needed for GC and CT since model calibration does not resolve the differences

Characterization of Molecular Cluster Detection and Evaluation of Cluster Investigation Criteria Using Machine Learning Methods and Statewide Surveillance Data in Washington State

Molecular cluster detection can be used to interrupt HIV transmission but is dependent on identifying clusters where transmission is likely. We characterized molecular cluster detection in Washington State, evaluated the current cluster investigation criteria, and developed a criterion using machine learning. The population living with HIV (PLWH) in Washington State, those with an analyzable genotype sequences, and those in clusters were described across demographic characteristics from 2015 to2018. The relationship between 3- and 12-month cluster growth and demographic, clinical, and temporal predictors were described, and a random forest model was fit using data from 2016 to 2017. The ability of this model to identify clusters with future transmission was compared to Centers for Disease Control and Prevention (CDC) and the Washington state criteria in 2018. The population with a genotype was similar to all PLWH, but people in a cluster were disproportionately white, male, and men who have sex with men. The clusters selected for investigation by the random forest model grew on average 2.3 cases (95% CI 1.1–1.4) in 3 months, which was not significantly larger than the CDC criteria (2.0 cases, 95% CI 0.5–3.4). Disparities in the cases analyzed suggest that molecular cluster detection may not benefit all populations. Jurisdictions should use auxiliary data sources for prediction or continue using established investigation criteria

Uptake and Population-Level Impact of Expedited Partner Therapy (EPT) on <i>Chlamydia trachomatis</i> and <i>Neisseria gonorrhoeae</i>: The Washington State Community-Level Randomized Trial of EPT

<div><p>Background</p><p>Expedited partner therapy (EPT), the practice of treating the sex partners of persons with sexually transmitted infections without their medical evaluation, increases partner treatment and decreases gonorrhea and chlamydia reinfection rates. We conducted a stepped-wedge, community-level randomized trial to determine whether a public health intervention promoting EPT could increase its use and decrease chlamydia test positivity and gonorrhea incidence in women.</p><p>Methods and Findings</p><p>The trial randomly assigned local health jurisdictions (LHJs) in Washington State, US, into four study waves. Waves instituted the intervention in randomly assigned order at intervals of 6–8 mo. Of the state’s 25 LHJs, 24 were eligible and 23 participated. Heterosexual individuals with gonorrhea or chlamydial infection were eligible for the intervention. The study made free patient-delivered partner therapy (PDPT) available to clinicians, and provided public health partner services based on clinician referral. The main study outcomes were chlamydia test positivity among women ages 14–25 y in 219 sentinel clinics, and incidence of reported gonorrhea in women, both measured at the community level. Receipt of PDPT from clinicians was evaluated among randomly selected patients. 23 and 22 LHJs provided data on gonorrhea and chlamydia outcomes, respectively. The intervention increased the percentage of persons receiving PDPT from clinicians (from 18% to 34%, <i>p</i> < 0.001) and the percentage receiving partner services (from 25% to 45%, <i>p</i> < 0.001). Chlamydia test positivity and gonorrhea incidence in women decreased over the study period, from 8.2% to 6.5% and from 59.6 to 26.4 per 100,000, respectively. After adjusting for temporal trends, the intervention was associated with an approximately 10% reduction in both chlamydia positivity and gonorrhea incidence, though the confidence bounds on these outcomes both crossed one (chlamydia positivity prevalence ratio = 0.89, 95% CI 0.77–1.04, <i>p</i> = 0.15; gonorrhea incidence rate ratio = 0.91, 95% CI .71–1.16, <i>p</i> = 0.45). Study findings were potentially limited by inadequate statistical power, by the institution of some aspects of the study intervention outside of the research randomization sequence, and by the fact that LHJs did not constitute truly isolated sexual networks.</p><p>Conclusions</p><p>A public health intervention promoting the use of free PDPT substantially increased its use and may have resulted in decreased chlamydial and gonococcal infections at the population level.</p><p>Trial Registration</p><p>ClinicalTrials.gov <a href="https://clinicaltrials.gov/ct2/show/NCT01665690" target="_blank">NCT01665690</a></p></div

Study population size and characteristics in local health jurisdictions in each study wave during the year prior to the intervention (October 2006–September 2007).

<p>Study population size and characteristics in local health jurisdictions in each study wave during the year prior to the intervention (October 2006–September 2007).</p

Characteristics of women tested for <i>C. trachomatis</i> in clinics providing outcome data for the trial compared to all women in areas of WA State participating in the trial.

<p>Characteristics of women tested for <i>C. trachomatis</i> in clinics providing outcome data for the trial compared to all women in areas of WA State participating in the trial.</p

Association of the study intervention with chlamydia test positivity and reported gonorrhea incidence in women.

<p>Association of the study intervention with chlamydia test positivity and reported gonorrhea incidence in women.</p

Trends in chlamydia test positivity and gonorrhea incidence for 2007–2010 among women in 23 local health jurisdictions in Washington State.

<p>Chlamydia test positivity and gonorrhea incidence (A) across all waves and (B) by wave. Open symbols and red lines indicate measurement and time before the institution of the study intervention, and solid symbols and black lines represent intervention time periods. Time periods are 3-mo analysis periods occurring prior to initiation of the intervention in each wave. </p

Study flow diagram.

<p>Modified for stepped-wedge design from suggested CONSORT criteria format for cluster randomized trials [<a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1001777#pmed.1001777.ref047" target="_blank">47</a>]. ⁺Numbers of tests and cases presented as means with ranges.</p