Factors Associated With Human Immunodeficiency Virus Infections Linked in Genetic Clusters But Disconnected in Partner Tracing.

BACKGROUND: Successful partner notification can improve community-level outcomes by increasing the proportion of persons living with human immunodeficiency virus (HIV) who are linked to HIV care and virally suppressed, but it is resource intensive. Understanding where HIV transmission pathways may be undetected by routine partner notification may help improve case finding strategies. METHODS: We combined partner notification interview and HIV sequence data for persons diagnosed with HIV in Wake County, NC in 2012 to 2013 to evaluate partner contact networks among persons with HIV pol gene sequences 2% or less pairwise genetic distance. We applied a set of multivariable generalized estimating equations to identify correlates of disparate membership in genetic versus partner contact networks. RESULTS: In the multivariable model, being in a male-male pair (adjusted odds ratio [AOR], 16.7; P = 0.01), chronic HIV infection status (AOR, 4.5; P < 0.01), and increasing percent genetic distance between each dyad member's HIV pol gene sequence (AOR, 8.3 per each 1% increase, P < 0.01) were all associated with persons with HIV clustering but not being identified in the partner notification network component. Having anonymous partners or other factors typically associated with risk behavior were not associated. CONCLUSIONS: Based on genetic networks, partnerships which may be stigmatized, may have occurred farther back in time or may have an intervening partner were more likely to be unobserved in the partner contact network. The HIV genetic cluster information contributes to public health understanding of HIV transmission networks in these settings where partner identifying information is not available.

Effects of Different Doses of GEN-003, a Therapeutic Vaccine for Genital Herpes Simplex Virus-2, on Viral Shedding and Lesions: Results of a Randomized Placebo-Controlled Trial.

Background: GEN-003 is a candidate therapeutic vaccine for genital herpes simplex virus type 2 (HSV-2). We compared virologic and clinical impact of varying GEN-003 doses. Methods: Adults with symptomatic HSV-2 received placebo or GEN-003 (30 or 60 µg antigen with 25, 50, or 75 µg adjuvant). Viral shedding and lesion rates before vaccination were compared with those measured immediately after vaccination, then at weeks 29-33 and 53-57 after last dose. Results: Compared with baseline shedding rates, the rate ratios for viral shedding immediately after treatment were as follows: 0.82 (95% confidence interval [CI], 0.49-1.36), 30 µg antigen/25 µg adjuvant (30/25) dose; 0.64 (95% CI, 0.45-0.92), 30/50 dose; 0.63 (95% CI, 0.37-1.10), 30/75 dose; 0.56 (95% CI, 0.36-0.88), 60/25 dose; 0.58 (95% CI, 0.38-0.89), 60/50 dose; 0.45 (95% CI, 0.16-0.79), 60/75 dose; and 0.98 (95% CI, 0.76-1.26), placebo. Lesion rate reductions by GEN-003 ranged from 31% to 69%, but lesion rates also decreased among placebo recipients (62%). Reductions in shedding and lesion rate were durable for 12 months for the 60 µg antigen plus 50 or 75 µg adjuvant groups. No serious adverse events occurred with vaccination. Conclusions: The most efficacious vaccine combinations for GEN-003 were the 60 µg/50 µg and 60 µg/75 µg doses.

Integration of Contact Tracing and Phylogenetics in an Investigation of Acute HIV Infection.

BACKGROUND: The integration of traditional contact tracing with HIV sequence analyses offers opportunities to mitigate some of the barriers to effective network construction. We used combined analyses during an outbreak investigation of spatiotemporally clustered acute HIV infections to evaluate if the observed clustering was the product of a single outbreak. METHODS: We investigated acute and recent HIV index cases reported in North Carolina from 2013 to 2014 and their reported contacts. Contact tracing networks were constructed with surveillance data and compared with phylogenetic transmission clusters involving an index case using available HIV-1 pol sequences including 1672 references. Clusters were defined as clades of 2 or more sequences with a less than 1.5% genetic distance and a bootstrap of at least 98% on maximum-likelihood phylogenies. RESULTS: In total, 68 index cases and 210 contacts (71 HIV infected) were reported. The contact tracing network involved 58 components with low overall density (1.2% statewide); 33% of first-degree contacts could not be located. Among 38 (56%) of 68 index cases and 34 (48%) of 71 contacts with sequences, 13 phylogenetic clusters were identified (size 2-4 members). Four clusters connected network components that were not linked in contact tracing. The largest component (n = 28 cases) included 2 distinct phylogenetic clusters and spanned 2 regions. CONCLUSIONS: We identified the concurrent expansion of multiple small transmission clusters rather than a single outbreak in a largely disconnected contact tracing network. Integration of phylogenetic analyses provided timely information on transmission networks during the investigation. Our findings highlight the potential of combined methods to better identify high-risk networks for intervention.

Association of perceived partner non-monogamy with prevalent and incident sexual concurrency.

OBJECTIVES: Concurrency is suggested as an important factor in sexually transmitted infection transmission and acquisition, though little is known regarding factors that may predict concurrency initiation. We examined the association between perception of a partner's non-monogamy (PPNM) and simultaneous or subsequent concurrency among at-risk heterosexual young adults in the Los Angeles area. METHODS: We used Poisson regression models to estimate the relationship between PPNM and incident concurrency among 536 participants participating in a cohort study, interviewed at 4-month periods during 1 year. Concurrency was defined as an overlap in reported sexual partnership dates; PPNM was defined as believing a partner was also having sex with someone else. RESULTS: Participants (51% female; 30% non-Hispanic white, 28% non-Hispanic black, 27% Hispanic/Latino) had a mean age of 23 years and lifetime median of nine sex partners. At each interview (baseline, 4-month, 8-month and 12-month), 4-month concurrency prevalence was, respectively, 38.8%, 27.4%, 23.1% and 24.5%. Four-month concurrency incidence at 4, 8 and 12 months was 8.5%, 10.6% and 17.8%, respectively. Participants with recent PPNM were more likely to initiate concurrency (crude 4-month RR=4.6; 95% CI 3.0, 7.0; adjusted 4-month RR=4.0, 95% CI 2.6 to 6.1). CONCLUSIONS: Recent PPNM was associated with incident concurrency. Among young adults, onset of concurrency may be stimulated, relatively quickly, by the PPNM. Programmes which promote relationship communication skills and explicit monogamy expectations may help reduce concurrency.

Variations in Clinical Presentation of Ocular Syphilis: Case Series Reported From a Growing Epidemic in the United States.

Ocular syphilis, a form of neurosyphilis, has been increasingly diagnosed in the United States. This case series summarizes the course of 6 patients recently diagnosed with ocular syphilis, emphasizing the varied sociodemographic factors and the wide range of symptoms and outcomes that are seen in patients with this disease.

Can Young Adults Accurately Report Sexual Partnership Dates? Factors Associated With Interpartner and Dyad Agreement.

BACKGROUND: Sexual partnership dates are critical to sexually transmitted infection/HIV research and control programs, although validity is limited by inaccurate recall and reporting. METHODS: We examined data from 302 heterosexual adults (151 index-partner dyads) to assess reliability of reporting. Dates of first sex and last sex were collected through individual interviews and joint dyad questionnaires, which were completed together with their partners. We compared index- and partner-reported dates to estimate interpartner agreement. We used log-linear regression to model associations between interpartner differences and partnership characteristics. To assess validity, we compared individually reported dates with those from joint dyad questionnaires. RESULTS: Most partnerships (66.2%) were 2 years or less in duration, and many (36.2%) were nonmonogamous. Interpartner agreement to within 1, 30, and 365 days was, respectively, 5.6%, 43.1%, and 81.3% for first sex, and 32.9%, 94.5%, and 100.0% for last sex. In adjusted models, longer relationship duration was associated with disagreement on first sex dates; partnership nonmonogamy was associated with disagreement on dates of first sex and last sex. Within dyads, several participant characteristics were associated with reporting dates closer to joint dyad responses (e.g., for first sex date, female sex [54.7%], having fewer sex partners [58.5%], and greater relationship commitment [57.3%]). However, percent agreement to within 30, 60, and 90 days was similar for all groups for both first and last sex dates. CONCLUSIONS: Agreement was high on date of last sex but only moderate on date of first sex. Methods to increase accuracy of reporting of dates of sex may improve STI research.

Influence of Detection Method and Study Area Scale on Syphilis Cluster Identification in North Carolina.

BACKGROUND: Identifying geographical clusters of sexually transmitted infections can aid in targeting prevention and control efforts. However, detectable clusters can vary between detection methods because of different underlying assumptions. Furthermore, because disease burden is not geographically homogenous, the reference population is sensitive to the study area scale, affecting cluster outcomes. We investigated the influence of cluster detection method and geographical scale on syphilis cluster detection in Mecklenburg County, North Carolina. METHODS: We analyzed primary and secondary syphilis cases reported in North Carolina (2003-2010). Primary and secondary syphilis incidence rates were estimated using census tract-level population estimates. We used 2 cluster detection methods: local Moran's I using an areal adjacency matrix and Kulldorff's spatial scan statistic using a variable size moving circular window. We evaluated 3 study area scales: North Carolina, Piedmont region, and Mecklenburg County. We focused our investigation on Mecklenburg, an urban county with historically high syphilis rates. RESULTS: Syphilis clusters detected using local Moran's I and Kulldorff's scan statistic overlapped but varied in size and composition. Because we reduced the scale to a high-incidence urban area, the reference syphilis rate increased, leading to the identification of smaller clusters with higher incidence. Cluster demographic characteristics differed when the study area was reduced to a high-incidence urban county. CONCLUSIONS: Our results underscore the importance of selecting the correct scale for analysis to more precisely identify areas with high disease burden. A more complete understanding of high-burden cluster location can inform resource allocation for geographically targeted sexually transmitted infection interventions.

Distance to testing sites and its association with timing of HIV diagnosis.

Early HIV diagnosis enables prompt treatment initiation, thereby contributing to decreased morbidity, mortality, and transmission. We aimed to describe the association between distance from residence to testing sites and HIV disease stage at diagnosis. Using HIV surveillance data, we identified all new HIV diagnoses made at publicly funded testing sites in central North Carolina during 2005-2013. Early-stage HIV was defined as acute HIV (antibody-negative test with a positive HIV RNA) or recent HIV (normalized optical density <0.8 on the BED assay for non-AIDS cases); remaining diagnoses were considered post-early-stage HIV. Street distance between residence at diagnosis and (1) the closest testing site and (2) the diagnosis site was dichotomized at 5 miles. We fit log-binomial models using generalized estimating equations to estimate prevalence ratios (PR) and robust 95% confidence intervals (CI) for post-early-stage diagnoses by distance. Models were adjusted for race/ethnicity and testing period. Most of the 3028 new diagnoses were black (N = 2144; 70.8%), men who have sex with men (N = 1685; 55.7%), and post-early-stage HIV diagnoses (N = 2010; 66.4%). Overall, 1145 (37.8%) cases traveled <5 miles for a diagnosis. Among cases traveling ≥5 miles for a diagnosis, 1273 (67.6%) lived <5 miles from a different site. Residing ≥5 miles from a testing site was not associated with post-early-stage HIV (adjusted PR, 95% CI: 0.98, 0.92-1.04), but traveling ≥5 miles for a diagnosis was associated with higher post-early HIV prevalence (1.07, 1.02-1.13). Most of the elevated prevalence observed in cases traveling ≥5 miles for a diagnosis occurred among those living <5 miles from a different site (1.09, 1.03-1.16). Modest increases in post-early-stage HIV diagnosis were apparent among persons living near a site, but choosing to travel longer distances to test. Understanding reasons for increased travel distances could improve accessibility and acceptability of HIV services and increase early diagnosis rates.

Efficacy results of a trial of a herpes simplex vaccine.

BACKGROUND: Two previous studies of a herpes simplex virus type 2 (HSV-2) subunit vaccine containing glycoprotein D in HSV-discordant couples revealed 73% and 74% efficacy against genital disease in women who were negative for both HSV type 1 (HSV-1) and HSV-2 antibodies. Efficacy was not observed in men or HSV-1 seropositive women. METHODS: We conducted a randomized, double-blind efficacy field trial involving 8323 women 18 to 30 years of age who were negative for antibodies to HSV-1 and HSV-2. At months 0, 1, and 6, some subjects received the investigational vaccine, consisting of 20 µg of glycoprotein D from HSV-2 with alum and 3-O-deacylated monophosphoryl lipid A as an adjuvant; control subjects received the hepatitis A vaccine, at a dose of 720 enzyme-linked immunosorbent assay (ELISA) units. The primary end point was occurrence of genital herpes disease due to either HSV-1 or HSV-2 from month 2 (1 month after dose 2) through month 20. RESULTS: The HSV vaccine was associated with an increased risk of local reactions as compared with the control vaccine, and it elicited ELISA and neutralizing antibodies to HSV-2. Overall, the vaccine was not efficacious; vaccine efficacy was 20% (95% confidence interval [CI], -29 to 50) against genital herpes disease. However, efficacy against HSV-1 genital disease was 58% (95% CI, 12 to 80). Vaccine efficacy against HSV-1 infection (with or without disease) was 35% (95% CI, 13 to 52), but efficacy against HSV-2 infection was not observed (-8%; 95% CI, -59 to 26). CONCLUSIONS: In a study population that was representative of the general population of HSV-1- and HSV-2-seronegative women, the investigational vaccine was effective in preventing HSV-1 genital disease and infection but not in preventing HSV-2 disease or infection. (Funded by the National Institute of Allergy and Infectious Diseases and GlaxoSmithKline; ClinicalTrials.gov number, NCT00057330.).

Large scale screening of human sera for HCV RNA and GBV-C RNA.

North Carolina locates acute HIV cases by pooled nucleic acid testing of HIV-antibody negative serum samples. Here, 224 pools of 80 HIV-negative samples (N = 17,920) were screened for viral RNA from HCV, GBV-C, and influenza A. No evidence of influenza A was found, but HCV and GBV-C were common (1.2% and 1.7% prevalence, respectively), demonstrating the utility of pooled testing in locating individuals that may remain undiagnosed otherwise. By sequencing positive pools, potential transmission clusters may be located as well.

Impact of a routine, opt-out HIV testing program on HIV testing and case detection in North Carolina sexually transmitted disease clinics.

BACKGROUND: The impact of routine, opt-out HIV testing programs in clinical settings is inconclusive. The objective of this study was to estimate the impact of an expanded, routine HIV testing program in North Carolina sexually transmitted disease (STD) clinics on HIV testing and case detection. METHODS: Adults aged 18 to 64 years who received an HIV test in a North Carolina STD clinic from July 1, 2005, through June 30, 2011, were included in this analysis, dichotomized at the date of implementation on November 1, 2007. HIV testing and case detection counts and rates were analyzed using interrupted time series analysis and Poisson and multilevel logistic regression. RESULTS: Preintervention, 426 new HIV-infected cases were identified from 128,029 tests (0.33%), whereas 816 new HIV-infected cases were found from 274,745 tests postintervention (0.30%). Preintervention, HIV testing increased by 55 tests per month (95% confidence interval [CI], 41-72), but only 34 tests per month (95% CI, 26-42) postintervention. Increases in HIV testing rates were most pronounced in women and non-Hispanic whites. A slight preintervention decline in case detection was mitigated by the intervention (mean difference, 0.01; 95% CI, -0.02 to 0.05). Increases in case detection rates were observed among women and non-Hispanic blacks. CONCLUSIONS: The impact of a routine HIV screening in North Carolina STD clinics was marginal, with the greatest benefit among persons not traditionally targeted for HIV testing. The use of a preintervention comparison period identified important temporal trends that otherwise would have been ignored.

HIV testing of tuberculosis patients by public and private providers in New York City.

Thirty percent of tuberculosis (TB) patients in New York City in 2007 were not tested for HIV, which may be attributable to differential testing behaviors between private and public TB providers. Adult TB cases in New York City from 2001 to 2007 (n = 5,172) were evaluated for an association between TB provider type (private or public) and HIV testing. Outcomes examined were offers of HIV tests and patient refusal of HIV testing, using multivariate logistic and binomial regression, respectively. HIV test offers were less frequent among patients who visited only private providers than patients who visited only public providers [males: adjusted odds ratio (aOR) 0.33, 95% confidence interval (CI) 0.15-0.74; females: aOR 0.26, 95% CI 0.12-0.57]. Changing from private to public providers was associated with an increase in HIV tests offered among male patients (aOR 1.96, 95% CI 1.04-3.70). Among patients who did not use substances, those who visited only private providers were more likely to refuse HIV testing than those who visited only public providers [males: adjusted prevalence ratio (aPR) 1.26, 95% CI 0.99-1.60; females: aPR 1.78, 95% CI 1.43-2.22]. Patients of private providers were less likely to have an HIV test performed during their TB treatment. Education of TB providers should emphasize HIV testing of all TB patients, especially among patients who are traditionally considered low-risk.

HSV-1 and HSV-2 seroprevalence in the united states among asymptomatic women unaware of any herpes simplex virus infection (Herpevac Trial for Women).

OBJECTIVES: Recent evidence suggests that the epidemiology of herpes simplex viruses (HSVs) is changing because fewer HSV-1 infections are acquired in childhood and increased sexual transmission of HSV-1 is reported. The objective of the study was to assess the seroprevalence of type-specific antibodies to HSV-1 and HSV-2 in the United States. METHODS: We used the Western blot antibody screening data from a large phase III vaccine efficacy trial (Herpevac Trial for Women) to assess the seroprevalence of type-specific antibodies to HSV-1 and HSV-2 in the United States. RESULTS: The antibody status of 29,022 women (>31,000 women interviewed and then had their blood drawn for the HSV testing [29,022 women]) between the ages of 18 and 30 years in the United States revealed that increasing age was associated with increasing seroprevalence to HSV. Overall, in asymptomatic women unaware of any HSV infection, HSV-1/-2 status was positive/negative in 45%, negative/positive in 5%, positive/positive in 7%, negative/negative in 38%, and indeterminate in 5%. HSV-1 infections were more common in Hispanic and non-Hispanic black women and in the US northeast and in individuals living in urban areas. HSV-2 was more common in non-Hispanic black women, the US south, and in urban areas. CONCLUSIONS: Seronegative status for both HSV-1 and HSV-2 was the second most common finding after positive antibody to HSV-1 but negative antibody to HSV-2. Despite recent changes in genital herpes epidemiology, most women acquired HSV-1 but not HSV-2 infections before 18 years of age. Among participants screened for study participation and who were unaware of any HSV infection, progressively higher prevalence of the HSV-1 or HSV-2 antibody was observed in older subjects. Many women who test positive for HSV-1 and/or HSV-2 are unaware of their status.

Progression of a large syphilis outbreak in rural North Carolina through space and time: Application of a Bayesian Maximum Entropy graphical user interface.

In 2001, the primary and secondary syphilis incidence rate in rural Columbus County, North Carolina was the highest in the nation. To understand the development of syphilis outbreaks in rural areas, we developed and used the Bayesian Maximum Entropy Graphical User Interface (BMEGUI) to map syphilis incidence rates from 1999-2004 in seven adjacent counties in North Carolina. Using BMEGUI, incidence rate maps were constructed for two aggregation scales (ZIP code and census tract) with two approaches (Poisson and simple kriging). The BME maps revealed the outbreak was initially localized in Robeson County and possibly connected to more urban endemic cases in adjacent Cumberland County. The outbreak spread to rural Columbus County in a leapfrog pattern with the subsequent development of a visible low incidence spatial corridor linking Roberson County with the rural areas of Columbus County. Though the data are from the early 2000s, they remain pertinent, as the combination of spatial data with the extensive sexual network analyses, particularly in rural areas gives thorough insights which have not been replicated in the past two decades. These observations support an important role for the connection of micropolitan areas with neighboring rural areas in the spread of syphilis. Public health interventions focusing on urban and micropolitan areas may effectively limit syphilis indirectly in nearby rural areas.

Sustained Virologic Suppression With Dolutegravir/Lamivudine in a Test-and-Treat Setting Through 48 Weeks.

Background: We assessed the efficacy and safety of dolutegravir/lamivudine (DTG/3TC) in a US test-and-treat setting at a secondary 48-week time point of the multicenter, single-arm, phase IIIb STAT study. Methods: Participants were eligible adults newly diagnosed with human immunodeficiency virus (HIV)-1 and had started once-daily DTG/3TC within 14 days of diagnosis, before laboratory results were available. Antiretroviral therapy (ART) was modified if baseline testing indicated DTG or 3TC resistance, hepatitis B virus (HBV) coinfection, or creatinine clearance <30 mL/min per 1.73 m2, and these participants remained in the study. A proportion with HIV-1 ribonucleic acid (RNA) <50 copies/mL at Week 48 was calculated among all participants (intention-to-treat-exposed [ITT-E] missing = failure analysis) and those with available data (observed analysis). Results: At Week 48, 82% of all participants regardless of ART (107 of 131; ITT-E missing = failure) and 97% with available data (107 of 110; observed analysis) achieved HIV-1 RNA <50 copies/mL. High proportions of virologic response were seen overall, including in participants with high viral load (≥500 000 copies/mL; 89%) or low CD4+ cell count (<200 cells/mm3; 78%) at baseline. Ten participants had treatment modification (baseline HBV coinfection, n = 5; participant/proxy decision, n = 2; baseline M184V resistance mutation, adverse event [AE; rash], and pregnancy, n = 1 each) before Week 48. Two participants met confirmed virologic failure criteria. No treatment-emergent resistance was observed. Ten participants reported drug-related AEs (all grade 1-2); no serious drug-related AEs occurred. Conclusions: Results demonstrated high proportions of participants with sustained virologic suppression, no treatment-emergent resistance, and good safety over 48 weeks, supporting first-line use of DTG/3TC in a test-and-treat setting.

Sexual networks, surveillance, and geographical space during syphilis outbreaks in rural North Carolina.

BACKGROUND: Sexually transmitted infections (STIs) spread along sexual networks whose structural characteristics promote transmission that routine surveillance may not capture. Cases who have partners from multiple localities may operate as spatial network bridges, thereby facilitating geographical dissemination. We investigated how surveillance, sexual networks, and spatial bridges relate to each other for syphilis outbreaks in rural counties of North Carolina. METHODS: We selected from the state health department's surveillance database cases diagnosed with primary, secondary, or early latent syphilis during October 1998 to December 2002 and who resided in central and southeastern North Carolina, along with their sex partners and their social contacts irrespective of infection status. We applied matching algorithms to eliminate duplicate names and create a unique roster of partnerships from which networks were compiled and graphed. Network members were differentiated by disease status and county of residence. RESULTS: In the county most affected by the outbreak, densely connected networks indicative of STI outbreaks were consistent with increased incidence and a large case load. In other counties, the case loads were low with fluctuating incidence, but network structures suggested the presence of outbreaks. In a county with stable, low incidence and a high number of cases, the networks were sparse and dendritic, indicative of endemic spread. Outbreak counties exhibited densely connected networks within well-defined geographic boundaries and low connectivity between counties; spatial bridges did not seem to facilitate transmission. CONCLUSIONS: Simple visualization of sexual networks can provide key information to identify communities most in need of resources for outbreak investigation and disease control.

Developing a predictive model to prioritize human immunodeficiency virus partner notification in North Carolina.

BACKGROUND: Disease intervention specialists (DIS) in North Carolina have less time to conduct partner notification because of competing responsibilities while simultaneously facing increased case loads because of increased human immunodeficiency virus (HIV) testing. We developed a model to predict undiagnosed HIV infection in sexual partners to prioritize DIS interviews. METHODS: We abstracted demographic, behavioral, and partnership data from DIS records of HIV-infected persons reported in 2 North Carolina surveillance regions between January 1, 2003 and December 31, 2007. Multiple logistic regression with generalized estimating equations was used to develop a predictive model and risk scores among newly diagnosed persons and their partners. Sensitivities and specificities of the risk scores at different cutoffs were used to examine algorithm performance. RESULTS: Five factors predicted a partnership between a person with newly diagnosed HIV infection and an undiagnosed partner--a period of 4 weeks or fewer between HIV diagnosis and DIS interview, no history of crack use, no anonymous sex, fewer total sexual partners reported to DIS, and sexual partnerships between an older index case and younger partner. Using this model, DIS could choose an appropriate cutoff for locating a particular partner by determining the weight of false negatives relative to false positives. CONCLUSIONS: Although the overall predictive power of the model is low, it is possible to reduce the number of partners that needs to be located and interviewed while maintaining high sensitivity. If DIS continue to pursue all partners, the model would be useful in identifying partners in whom to invest more resources for locating.

Comparison of sexual mixing patterns for syphilis in endemic and outbreak settings.

BACKGROUND: In a largely rural region of North Carolina during 1998-2002, outbreaks of heterosexually transmitted syphilis occurred, tied to crack cocaine use and exchange of sex for drugs and money. Sexual partnership mixing patterns are an important characteristic of sexual networks that relate to transmission dynamics of sexually transmitted infections (STIs). METHODS: Using contact tracing data collected by disease intervention specialists, we estimated Newman assortativity coefficients and compared values in counties experiencing syphilis outbreaks to nonoutbreak counties, with respect to race/ethnicity, race/ethnicity and age, and the cases' number of social/sexual contacts, infected contacts, sex partners, and infected sex partners, and syphilis disease stage (primary, secondary, early latent). RESULTS: Individuals in the outbreak counties had more contacts and mixing by the number of sex partners was disassortative in outbreak counties and assortative nonoutbreak counties. Although mixing by syphilis disease stage was minimally assortative in outbreak counties, it was disassortative in nonoutbreak areas. Partnerships were relatively discordant by age, especially among older white men, who often chose considerably younger female partners. CONCLUSIONS: Whether assortative mixing exacerbates or attenuates the reach of STIs into different populations depends on the characteristic/attribute and epidemiologic phase. Examination of sexual partnership characteristics and mixing patterns offers insights into the growth of STI outbreaks that complement other research methods.