Research

A comprehensive listing of all my published research may be found on PubMed or at my Google Scholar profile. Below I list key papers by scientific area to summarize the major themes of my research portfolio.

Mathematical Modeling of HIV and STI Transmission Dynamics

Mathematical modeling has been used extensively within HIV prevention science to study relationships between individual-level inputs (e.g., behavioral and biology) and population-level outcomes (e.g., HIV prevalence and incidence). Through this framework, models may provide insight into the historical etiology and potential future directions of HIV at the population level, as well as possible mechanisms to reduce HIV incidence over time. Models may be used to test novel hypotheses where empirical research may be infeasible, unethical, or costly.

In addition to the methodological work described on the Software page, my substantive interests in modeling focus on estimating the epidemiological impact and efficiency of HIV prevention approaches such as preexposure prophylaxis (PrEP) among MSM and medical male circumcision in heterosexual men in Sub-Saharan Africa. This work has involved synthesizing secondary research and conducting primary data analysis for model parameters, building computational epidemic models of these interventions, and analyzing the data from models outputs. Through this applied modeling, I have interests in linking field data collection efforts to modeling activities and in building models with realistic sexual network representations that are critical for prevention intervention targeting.

Representative Publications

Objectives. Combination packages for HIV prevention can leverage the effectiveness of biomedical and behavioral elements to lower disease incidence with realistic targets for individual and population risk reduction. We investigated how sexual network structures can maximize the effectiveness of a package targeting sexually active adults in Sub-Saharan Africa (SSA) with intervention components for medical male circumcision (MMC) and sexual partnership concurrency (having >1 ongoing partner).

Methods. Network-based mathematical models of HIV-1 transmission dynamics among heterosexual couples were used to explore how changes to MMC alone and in combination with changes to concurrency impacted endemic HIV-1 prevalence and incidence. Starting from a base model parameterized from empirical data from West Africa, we simulated the prevalence of circumcision from 10% to 90% and concurrency was modeled at four discrete levels corresponding to values observed across SSA.

Results. MMC and concurrency could contribute to the empirical variation in HIV-1 disease prevalence across SSA. Small reductions in concurrency resulted in large declines in HIV-1 prevalence. Scaling-up circumcision in low-concurrency settings yields a greater relative benefit, but the absolute number of infections averted depends on both the circumcision coverage and baseline incidence. Epidemic extinction with this package will require substantial scale-up of MMC in low-concurrency settings.

Conclusions. Dynamic sexual network structure should be considered in the design and targeting of MMC within combination HIV-1 prevention packages. Realistic levels of coverage for these packages within southern Africa could lead to a reduction of incidence to the low levels observed in western Africa, and possibly, epidemic extinction.

Jenness SM, Goodreau SM, Rosenberg E, Beylerian EN, Hoover KW, Smith DK, Sullivan PS. Impact of CDC’s HIV Pre-Exposure Prophylaxis Guidelines among MSM in the United States. Journal of Infectious Diseases. 2016; 214(12): 1800-1807.

Background. Pre-exposure prophylaxis (PrEP) is effective for preventing HIV infection among men who have sex with men (MSM) within trial settings. Population impact will depend on clinical indications for PrEP initiation, coverage levels, and drug adherence. No studies have estimated the impact of CDC’s clinical practice guidelines for PrEP.

Methods. Mathematical models of HIV transmission among MSM were used to estimate the proportion of infections averted (PIA) and the number needed to treat (NNT) under behavioral indications of the CDC’s PrEP guidelines. We modeled the contribution of these indications while varying treatment coverage and adherence.

Results. At 40% coverage of indicated MSM over the next decade, application of CDC guidelines would avert 1162 infections per 100,000 person-years, 33.0% of expected infections. The predicted NNT for the guidelines would be 25. Increasing coverage and adherence jointly raise the PIA, but reductions to the NNT were associated with better adherence only.

Conclusions. Implementation of CDC PrEP guidelines would result in strong and sustained reductions in HIV incidence among MSM in the US. The guidelines strike a good balance between epidemiological impact (PIA) and efficiency (NNT) at plausible scale-up levels. Adherence counseling could maximize public health investment in PrEP by decreasing the NNT.

Multi-Level Risk Factors for HIV and STI Acquisition

Understanding the etiology of infection for sexual transmitted infections is necessary to target disease prevention interventions towards at-risk persons. Transmission and acquisition risk have been particularly challenging to define within concentrated HIV epidemics where individual risk factors like recent multiple partnerships may be insufficient to fully characterize excesses in infection probability. My research in this domain has investigated the social, structural, and network-level factors for HIV/STI infection among key high-risk groups, including MSM in the United States and heterosexuals in both the US and Sub-Saharan Africa.

Representative Publications

Jenness SM, Begier E, Neaigus A, Murrill CS, Wendel T, Hagan H. Unprotected Anal Intercourse and Sexually Transmitted Diseases in High-Risk Heterosexual Women. American Journal of Public Health. 2011; 101(4): 745-750.

Objectives. We examined the association between unprotected anal intercourse and sexually transmitted diseases (STDs) among heterosexual women.

Methods. In 2006 through 2007, women were recruited from high-risk areas in New York City through respondent-driven sampling as part of the National HIV Behavioral Surveillance study. We used multiple logistic regression to determine the relationship between unprotected anal intercourse and HIV infection and past-year STD diagnosis.

Results. Of the 436 women studied, 38% had unprotected anal intercourse in the past year. Unprotected anal intercourse was more likely among those who were aged 30 to 39 years, were homeless, were frequent drug or binge alcohol users, had an incarcerated sexual partner, had sexual partners with whom they exchanged sex for money or drugs, or had more than 5 sexual partners in the past year. In the logistic regression, women who had unprotected anal intercourse were 2.6 times as likely as women who had only unprotected vaginal intercourse and 4.2 times as likely as women who had neither unprotected anal nor unprotected vaginal intercourse to report an STD diagnosis. We found no significant association between unprotected anal intercourse and HIV infection.

Conclusions. Increased screening for history of unprotected anal intercourse and, for those who report recent unprotected anal intercourse, counseling and testing for HIV and STDs would likely reduce STD infections.

Jenness SM, Hagan H, Wendel T, Murrill CS, Neaigus A, Gelpi-Acosta C. Reconsidering the Internet as an HIV/STD Risk for Men Who Have Sex with Men. AIDS & Behavior. 2010; 14(6): 1353-1361.

Previous studies linking online sexual partnerships to behavioral risks among men who have sex with men (MSM) may be subject to confounding and imprecise measurement of partnership-specific risks. We examined behavioral risks associated with having only online, only offline, or both online and offline partners in the past year, the confounding effects of multiple partnerships, and partnership-specific risks among a sample of MSM from New York City recruited offline in 2008. Overall, 28% of 479 participants had an online partner in the past year, but most of those (82%) also had an offline partner. Having an online partner was associated with past-year unprotected anal intercourse (UAI) and other risks, but not after controlling for multiple partnerships. There were slightly higher levels of risk within offline partnerships, but differences were largely attributable to MSM who had both offline and online partners. Last sex partners met offline were more likely to be HIV-serodiscordant and engage in concurrent substance use with the participant. This suggests that online partnerships may not be an independent cause of behavioral risks, but a marker for risks occurring independent of Internet use.

Jenness SM, Neaigus A, Hagan H, Murrill CS, Wendel T. HIV Infection and Sexual Partnerships between Injection Drug Users and Non-Injectors. AIDS Patient Care & STDS. 2010; 24(3): 175-181.

Sex partnerships with injection drug users (IDU) are an understudied network-level risk factor for heterosexual HIV infection. Heterosexuals with no history of injection were recruited from high-risk areas in New York City through respondent-driven sampling. We examined the prevalence of IDU sex partnerships among these non-IDU, the factors associated with having a past year IDU partner, and the independent association of HIV infection and IDU sex partnerships in multiple logistic regression. Of the 601 non-IDU in this analysis, 13.8% had a sex partner in the past year with a history of injection. IDU partnerships were significantly more common among women and those with higher levels of unprotected sex and drug and alcohol use. Overall, 7.0% tested positive for HIV. HIV prevalence was higher (p = 0.07) for participants with IDU partners (9.6%) compared to those with no IDU partners (4.6%). In multiple logistic regression, participants with IDU partners were over twice as likely to be HIV-infected (p = 0.08). Sex partnerships with IDU were common and may play an important role in heterosexual HIV transmission in areas with large IDU populations. Prevention interventions to encourage the disclosure of injection history and risk reduction specifically for those with IDU partners are indicated.

Network Science for Infectious Disease Epidemiology

The configuration of sexual networks within a population plays a critical role in the spread of HIV and other sexually transmitted infections, yet characterizing the structure of dynamic networks in which epidemiologically relevant partnerships form and dissolve over time is challenging. Recent developments in statistics (temporal exponential random graph models), however, have yielded important new methods to allow for the recontruction and simulation of dynamic contact networks from easily collected data. These methods allow for testing hypotheses about the relationship between network configurations and transmission risk in innovative ways.

One example of a network hypothesis is sexual partner concurrency, which occurs when sexual acts with one partner temporally occur between acts with another. Small changes in the average number of partners (momentary mean degree) can have a substantial impact on population-level disease prevalence. Network-based risks like concurrency often have counterintuitive effects: an increase in momentary mean degree among men has the effect of increasing HIV incidence among women within heterosexual transmission networks.

My research in this area has focused on estimating key parameters relevant to HIV transmission dynamics, including rates of concurrency and the relationship between network degree and coital frequency. These estimates are useful by me and others in mathematical models of HIV to explore the implications of network structure in ways that are impossible with traditional epidemiological study designs.

Representative Publications

Jenness SM, Biney AA, Ampofo WK, Nii-Amoo Dodoo F, Cassels S. Minimal Coital Dilution in Accra, Ghana. Journal of Acquired Immune Deficiency Syndrome. 2015; 69: 85–91.

Background. Coital dilution, the reduction in the coital frequency per partner when an additional ongoing partner is added, may reduce the transmission potential of partnership concurrency for HIV and other sexually transmitted infections. Empirical estimates of dilution, especially dilution of sexual acts unprotected by condoms, are needed to inform prevention research.

Methods. Sexually active adults in Accra, Ghana were recruited in a multistage household probability sample. Degree (number of ongoing partners), total acts, and unprotected acts were measured retrospectively for each month in the past year through an event history calendar. Random-effects negative binomial models estimated the association between degree and coital frequency.

Results. Compared with person-months with a single partner (monogamy), 2.06 times as many total acts and 1.94 times as many unprotected acts occurred in months with 2 partners. In months with 3 partners, 2.90 times as many total acts and 2.39 times as many unprotected acts occurred compared with monogamous months. Total acts but not unprotected acts also declined with partnership duration.

Conclusions. No dilution was observed for total acts with up to 3 concurrent partners, but a small amount of dilution was observed for unprotected acts for months with multiple concurrencies. This suggests moderate selective condom use in months with multiple concurrencies. The implications of the observed dilution for future HIV transmission must be investigated with mathematical models.

Cassels S, Manhart L, Jenness SM, Morris M. Short-term Mobility and Increased Partnership Concurrency among Men in Zimbabwe. PloS One. 2013; 8(6): e66342.

Background. Migration has long been understood as an underlying factor for HIV transmission, and sexual partner concurrency has been increasingly studied as an important component of HIV transmission dynamics. However, less work has examined the role of short-term mobility in sexual partner concurrency using a network approach. Short-term mobility may be a risk for HIV for the migrant's partner as well either through the partner's risk behaviors while the migrant is away, such as the partner having additional partners, or via exposure to the return migrant.

Methods. Using data from the 2010-11 Zimbabwe Demographic and Health Survey, weighted generalized linear regression models were used to investigate the associations between short-term mobility and partnership concurrency at the individual and partnership levels.

Results. At the individual level, we find strong evidence of an association between short-term mobility and concurrency. Men who traveled were more likely to have concurrent partnerships compared to men who did not travel and the relationship was non-linear: each trip was associated with a 2% higher probability of concurrency, with a diminishing risk at 60 trips (p < 0.001). At the partnership level, short-term mobility by the male only or both partners was associated with male concurrency. Couples in which the female only traveled exhibited less male concurrency.

Conclusions. Short-term mobility has the ability to impact population-level transmission dynamics by facilitating partnership concurrency and thus onward HIV transmission. Short-term migrants may be an important population to target for HIV testing, treatment, or social and behavioral interventions to prevent the spread of HIV.

Methods for Unbiased Estimation in Survey Research

I have also been interested in the statistical and epidemiological methods for the estimation of characteristics of “hidden” populations, those who are difficult or impossible to sample with traditional probabilistic survey methods (e.g., random digit dialing and household-based recruitment). Two methods, respondent-driven sampling and venue-based sampling, have become increasingly popular both in the U.S. and internationally, but recent research suggests some systematic biases that impact statistical inference.

My research has investigated these biases among a large-scale venue-based study of men who have sex with men, and also the potential spatial bias within a respondent-driven sampling study of high-risk heterosexual adults in New York City. This work also involves using cross-sectional techniques to estimate HIV incidence, which may be only typically measured in expensive longitudinal cohorts.

Representative Publications

Jenness SM, Neaigus A, Murrill CS, Gelpi-Acosta C, Wendel T, Hagan H. Recruitment-Adjusted Estimates of HIV Prevalence and Risk Among Men Who Have Sex with Men: Effects of Weighting Venue-Based Sampling Data. Public Health Reports. 2011; 126(5): 635-642.

Objectives. We investigated the impact of recruitment bias within the venue-based sampling (VBS) method, which is widely used to estimate disease prevalence and risk factors among groups, such as men who have sex with men (MSM), that congregate at social venues.

Methods. In a 2008 VBS study of 479 MSM in New York City, we calculated venue-specific approach rates (MSM approached/MSM counted) and response rates (MSM interviewed/MSM approached), and then compared crude estimates of HIV risk factors and seroprevalence with estimates weighted to address the lower selection probabilities of MSM who attend social venues infrequently or were recruited at high-volume venues.

Results. Our approach rates were lowest at dance clubs, gay pride events, and public sex strolls, where venue volumes were highest; response rates ranged from 39% at gay pride events to 95% at community-based organizations. Sixty-seven percent of respondents attended MSM-oriented social venues at least weekly, and 21% attended such events once a month or less often in the past year. In estimates adjusted for these variations, the prevalence of several past-year risk factors (e.g., unprotected anal intercourse with casual/exchange partners, ≥5 total partners, group sex encounters, at least weekly binge drinking, and hard-drug use) was significantly lower compared with crude estimates. Adjusted HIV prevalence was lower than unadjusted prevalence (15% vs. 18%), but not significantly.

Conclusions. Not adjusting VBS data for recruitment biases could overestimate HIV risk and prevalence when the selection probability is greater for higher-risk MSM. While further examination of recruitment-adjustment methods for VBS data is needed, presentation of both unadjusted and adjusted estimates is currently indicated.

Jenness SM, Neaigus A, Wendel T, Gelpi-Acosta C, Hagan H. Spatial recruitment bias in respondent-driven sampling: Implications for HIV prevalence estimation in urban heterosexuals. AIDS & Behavior. 2014; 18(12): 2366-73.

Respondent-driven sampling (RDS) is a study design used to investigate populations for which a probabilistic sampling frame cannot be efficiently generated. Biases in parameter estimates may result from systematic non-random recruitment within social networks by geography. We investigate the spatial distribution of RDS recruits relative to an inferred social network among heterosexual adults in New York City in 2010. Mean distances between recruitment dyads are compared to those of network dyads to quantify bias. Spatial regression models are then used to assess the impact of spatial structure on risk and prevalence outcomes. In our primary distance metric, network dyads were an average of 1.34 (95 % CI 0.82–1.86) miles farther dispersed than recruitment dyads, suggesting spatial bias. However, there was no evidence that demographic associations with HIV risk or prevalence were spatially confounded. Therefore, while the spatial structure of recruitment may be biased in heterogeneous urban settings, the impact of this bias on estimates of outcome measures appears minimal.

Jenness SM, Neaigus A, Murrill CS, Gelpi-Acosta C, Wendel T, Hagan H. Estimated HIV Incidence among High-Risk Heterosexuals in New York City, 2007. Journal of Acquired Immune Deficiency Syndrome. 2011; 56(2): 193-197.

Estimates of HIV incidence rates among high-risk heterosexuals (HRH) in the United States have been limited to heterosexual subgroups like prison inmates and commercial sex workers. In this analysis, we estimate incidence with detuned assay testing among a group of HRH defined through a multidimensional sampling strategy and recruited through respondent-driven sampling. Incidence was 3.31% per year (95% confidence interval = 1.43 to 6.47) overall and 2.59% per year (95% confidence interval = 0.84 to 6.06) among participants with no lifetime history of drug injection or male-to-male sex. This study design is suggested as an efficient method for recruiting HRH for cohort studies and behavioral interventions.

Demographic Dynamics & Infectious Disease

With Susan Cassels, we are currently investigating the implications of migration and mobility on HIV transmission dynamics within an urban slum neighborhood in Accra, Ghana. This research involved primary data collection during the summer of 2012, in which we conducted a household-based cross-sectional study of sexually active adults. Study procedures included a detailed structured survey and a diagnostic HIV-1/2 test. In addition to the main probability sample, a secondary sample of cohabiting sexual partners were recruited, with data linkages to the main survey.

Our goal is to use traditional statistical analysis and stochastic mathematical modeling to investigate the relationships between migration/mobility, sexual partner concurrency, and HIV transmission in Ghana and other West African countries. We are also interesting in discussing and developing the methods for epidemiological research in populations with high rates of demographic turnover, as measuring disease prevalence and risk factors becomes complicated in highly-mobile or high-mortality areas.

Representative Publications

Cassels S, Jenness SM, Biney AA, Ampofo WK, Dodoo RN. Migration, sexual networks, and HIV in Agbogbloshie, Ghana. Demographic Research. 2014; 31: 861-888.

Background. HIV is spread through structured sexual networks, which are influenced by migration patterns, but network-oriented studies of mobility and HIV risk behavior have been limited.

Objectives. We present a comprehensive description and initial results from our Migration & HIV in Ghana (MHG) study in Agbogbloshie, an urban slum area within Accra, Ghana.

Methods. The MHG study was a population-based cross-sectional study of adults aged 18-49 in Agbogbloshie in 2012. We used a one-year retrospective relationship history calendar to collect egocentric network data on sexual partners as well as migration and short-term mobility, and tested for prevalent HIV-1/2 infection.

Results. HIV prevalence was 5.5%, with prevalence among women (7.2%) over twice that of men (2.8%). Three-quarters of residents were born outside the Greater Accra region, but had lived in Agbogbloshie an average of 10.7 years. Only 7% had moved housing structures within the past year. However, short-term mobility was common. Residents had an average of 7.3 overnight trips in the last year, with women reporting more travel than men. Thirty-seven percent of men and 9% of women reported more than one sexual partner in the last year.

Conclusions. Population-based surveys of migration and sexual risk behavior using relationship history calendars in low-resource settings can produce high quality data. Residents in Agbogbloshie are disproportionately affected by HIV, and have high levels of short-term mobility. HIV prevention interventions targeted to highly mobile populations in high prevalence settings may have far-reaching and long-term implications.

Cassels S, Jenness SM, Khanna AS. Conceptual framework and research methods for migration and HIV transmission dynamics. AIDS & Behavior. 2014; 18(12): 2302-13.

Migration and mobility have had a profound influence on the global HIV epidemic. We propose a network-dyadic conceptual model to interpret previous literature and inform the development of future research with respect to study design, measurement methods, and analytic approach. In this model, HIV transmission is driven by risk behaviors of migrants that emerges and is enabled by mobility, the bridging of sub-epidemics across space and time, and the displacement effects on the primary residential sending community for migrants. To investigate these causal pathways, empirical study designs must measure the relative timing of migratory events, sexual risk behaviors, and incident HIV infections. Network-based mathematical models using empirical data on partnerships help gain insight into the dynamic disease transmission systems. Although the network-dyadic conceptual model and related network methods may not address all questions related to migration and HIV, they provide a unified approach for future research on this important topic.