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Invited Commentary
Public Health
December 14, 2018

The Epidemiology of Sexual Partnerships—It’s Complicated

Author Affiliations
  • 1Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
  • 2Institute of Health Policy, Management, and Evaluation, University of Toronto, Toronto, Ontario, Canada
  • 3Department of Global Health and Population, Harvard T.H. Chan School of Public Health, Boston, Massachusetts
JAMA Netw Open. 2018;1(8):e185997. doi:10.1001/jamanetworkopen.2018.5997

Sexually transmitted infections (STIs) remain an important source of morbidity and diminished quality of life worldwide.1 The reproductive health consequences include pelvic inflammatory disease, ectopic pregnancy, infertility, and congenital infections. When HIV and mortality from cancers linked to sexually transmitted viruses (hepatitis B and human papillomavirus in particular) are considered, they are also a major source of mortality. Key to devising effective prevention and control strategies is understanding the epidemiology of STIs, which in turn requires an understanding of the dynamics of sexual partnerships and the individual behaviors that influence infection acquisition and transmission. However, as the study by Mercer et al2 demonstrates, such an enterprise is not simply a matter of linking total sexual partner numbers to STI risk. Different types of partnerships (differing in duration, frequency of sex, risk-taking behaviors, and concurrency), and how those partnerships fit into sexual networks, may have very different consequences for STI transmission and observed STI epidemiology.3

Mercer et al2 presented an analysis of self-reported sexual partnership data and self-reported STI history from the third British National Survey of Sexual Attitudes and Lifestyles, which has been performed at approximately 10-year intervals since 1990.4 Notwithstanding the potential limitations of this survey (self-report, self-selection by survey participants), it represents a unique source for studying general-population sexual behaviors and risk factors associated with STIs. Rather than simply asking about sex partner numbers over time, Mercer et al2 attempted to place egocentric partnership data in a broader context by asking whether partnerships were serial or concurrent; participants were also asked about their perceptions of concurrency in their sex partners. The distinction has epidemiological importance, as simultaneous partnering by an individual with 2 (or more) other individuals allows that individual to serve as a bridge between those 2 partners. If those partnerships occurred in series, with a temporal gap between them, the risk that the second partner will be infected with a pathogen infecting the first partner may be diminished, depending on the duration of the gap and the duration of infectivity of the pathogen in question.5 The infectivity of the most common STIs (most notably gonorrhea, and likely chlamydia) is likely to decline within months of initial infection. Symptomatic recurrences of genital herpes simplex virus infections also decline over time following initial infection, although there is additional complexity in this situation owing to risk of infection via ongoing subclinical shedding. The results of the study by Mercer et al2 support the importance of partnership gaps for STI transmission, with the finding that individuals who report longer gaps between serial partnerships are less likely to also report having been diagnosed with an STI, even after adjustment for total partner numbers and age.

Also interestingly, and perhaps unexpectedly, the lowest quartile of gap lengths became increasingly negative (ie, individuals were likely to have longer concurrent partnerships) as they aged, suggesting more stable concurrency in older individuals than in younger individuals. Individuals were asked about perceptions of their partners’ concurrency, and those who answered with a firm “no” to the question of whether their partners had other partners were less likely to report STI diagnosis; this effect was seen in both men and women. The more partners an individual reported, the more likely they were to think their partners had concurrent partners; this was also associated with self-reported STI diagnosis. One must ask whether self-reported concurrency serves as a valid indirect marker of the likelihood that the individual’s sex partners themselves have concurrent partnerships; we did not see this addressed in the article, although the likelihood of perceived partner concurrency did rise with increasing partner numbers. We might hypothesize that there is a correlation between self-reported concurrency and perceived partner concurrency, as there is a substantial body of evidence suggesting that sex partner selection is “assortative” with respect to sex behaviors.3 In other words, we tend to choose partners who are more, rather than less, similar to us with respect to sexual behaviors.

While the authors’ findings have substantial face validity, it is important to remember that both partnership characteristics and STI diagnosis histories were self-reported in the third British National Survey of Sexual Attitudes and Lifestyles. The reliance on egocentric data sets the limits for this analysis and we are left with an incomplete picture of an individual’s underlying sexual network. Furthermore, the temporal relationship between STI diagnosis and short gaps and concurrency is not included in the analysis. As large fractions of STIs are likely undiagnosed or underdiagnosed,6 one possible alternate interpretation of the data presented was that individuals who are more likely to have concurrent partnerships, or who perceive their partners to be riskier, were more likely to seek screening for STIs. In societies that stigmatize STIs, and in which there may be both normative and structural barriers to STI testing, increased likelihood of STI reporting could indeed reflect individuals being more actively invested in caring for their own sexual health.

This study highlights the complexity of sexual partnerships and the challenges associated with correlating sexual behavior with STI risk. In many high-income countries over the past few decades, the burden of some STIs, notably syphilis and gonorrhea, was concentrated in higher-risk core groups (those who contribute disproportionately to disease transmission).7 However, in recent years there has been an overall trend of increasing incidence of these STIs and a consequent shift in their epidemiology, with increased case occurrence, and consequently, associated severe outcomes,8 in what have typically been considered lower-risk groups. Simple self-reported metrics, such as gap length between recent partnerships or perceived partner concurrency, may provide useful information that could help public health professionals to develop more nuanced STI screening tools to identify at-risk individuals who may not report behaviors commonly used to identify core groups. However, it should be noted that overemphasis on individuals’ sex behaviors in the clinical setting may increase stigma, while at the same time do little to change either structural or population-level factors that drive STI risk.9 Consequently, using resources to lower risk in hard-to-reach and disadvantaged populations may be more effective in lowering population risk than focusing on the wider population.

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Article Information

Published: December 14, 2018. doi:10.1001/jamanetworkopen.2018.5997

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2018 Tuite AR et al. JAMA Network Open.

Corresponding Author: Ashleigh R. Tuite, PhD, Dalla Lana School of Public Health, University of Toronto, 209 Victoria St, Toronto, ON M5B 1T8, Canada (ashleigh.tuite@utoronto.ca).

Conflict of Interest Disclosures: None reported.

References
1.
Unemo  M, Bradshaw  CS, Hocking  JS,  et al.  Sexually transmitted infections: challenges ahead.  Lancet Infect Dis. 2017;17(8):e235-e279. doi:10.1016/S1473-3099(17)30310-9PubMedGoogle ScholarCrossref
2.
Mercer  CH, Jones  KG, Geary  RS,  et al.  Association of timing of sexual partnerships and perceptions of partners’ concurrency with reporting of sexually transmitted infection diagnosis.  JAMA Netw Open. 2018;1(8): e185957. doi:10.1001/jamanetworkopen.2018.5957Google Scholar
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Doherty  IA, Padian  NS, Marlow  C, Aral  SO.  Determinants and consequences of sexual networks as they affect the spread of sexually transmitted infections.  J Infect Dis. 2005;191(suppl 1):S42-S54. doi:10.1086/425277PubMedGoogle ScholarCrossref
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Mercer  CH, Wellings  K, Johnson  AM.  What’s new about Natsal-3?  Sex Transm Infect. 2014;90(2):80-81. doi:10.1136/sextrans-2013-051292PubMedGoogle ScholarCrossref
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Chen  MI, Ghani  AC, Edmunds  J.  Mind the gap: the role of time between sex with two consecutive partners on the transmission dynamics of gonorrhea.  Sex Transm Dis. 2008;35(5):435-444. doi:10.1097/OLQ.0b013e3181612d33PubMedGoogle ScholarCrossref
6.
Turner  CF, Rogers  SM, Miller  HG,  et al.  Untreated gonococcal and chlamydial infection in a probability sample of adults.  JAMA. 2002;287(6):726-733. doi:10.1001/jama.287.6.726PubMedGoogle ScholarCrossref
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Aral  SO, Fenton  KA, Holmes  KK.  Sexually transmitted diseases in the USA: temporal trends.  Sex Transm Infect. 2007;83(4):257-266. doi:10.1136/sti.2007.026245PubMedGoogle ScholarCrossref
8.
Furegato  M, Fifer  H, Mohammed  H,  et al.  Factors associated with four atypical cases of congenital syphilis in England, 2016 to 2017: an ecological analysis.  Euro Surveill. 2017;22(49). doi:10.2807/1560-7917.ES.2017.22.49.17-00750PubMedGoogle Scholar
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Mapp  F, Wellings  K, Hickson  F, Mercer  CH.  Understanding sexual healthcare seeking behaviour: why a broader research perspective is needed.  BMC Health Serv Res. 2017;17(1):462. doi:10.1186/s12913-017-2420-zPubMedGoogle ScholarCrossref
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