Assortative sexual mixing patterns in male-female and male-male partnerships in Melbourne, Australia: implications for HIV and sexually transmissible infection transmission

Assortative Sexual Mixing by Age, Region of Birth, and Time of Arrival in Male-Female Partnerships in Melbourne, Australia

BACKGROUND

Patterns of sexual mixing may be influenced by demographic factors where individuals show a preference for partners with particular traits and may have different levels of risk for HIV and sexually transmitted infection transmission. We aimed to explore age differences and mixing by region of birth among male-female partnerships.

METHODS

Male-female partnerships who presented to Melbourne Sexual Health Centre in Australia between 2015 and 2019 were investigated. Age and country of birth of sexual partners were collected. We calculated the age differences between partners and created tables demonstrating partnership mixing by age groups and by international region of birth.

RESULTS

A total of 2112 male-female partnerships (i.e., 4224 individuals) were included. The median age was 27 years (interquartile range, 23-31 years). Between men and women in partnerships, the median age difference was 1 year. Nearly half of all individuals (49.1% [2072 of 4224]) were in a partnership with another individual in the same 5-year interval age group as their own, and a majority of individuals (58.5% [2334 of 3988]) were in a partnership with another individual from the same region of birth when compared with other regions.

CONCLUSIONS

There is a strong assortative sexual mixing pattern by age and region of birth among male-female partnerships in Melbourne, Australia. These results may have applications in further research to understand sexually transmitted infection transmission among clients attending sexual health centers, particularly those born overseas.

Human papillomavirus vaccine coverage in male-male partnerships attending a sexual health clinic in Melbourne, Australia

We aimed to investigate the sexual mixing by human papillomavirus (HPV) vaccination status in male-male partnerships and estimate the proportion of male-male partnerships protected against HPV. We analyzed male-male partnerships attending the Melbourne Sexual Health Center between 2018 and 2019. Data on self-reported HPV vaccination status were collected. Newman’s assortativity coefficient was used to examine the sexual mixing by HPV vaccination status. Assortativity refers to the tendency of individuals to have partners with similar characteristics (i.e. same vaccination status). Of 321 male-male partnerships where both men reported their HPV vaccination status, 52.6% (95% CI: 47.0–58.2%) partnerships had both men vaccinated, 32.1% (95% CI: 27.0–37.5%) partnerships had only one man vaccinated, and 15.3% (95% CI: 11.5–19.7%) had both men unvaccinated. The assortativity on HPV vaccination status was moderate (assortativity coefficient = 0.265, 95% CI: 0.196–0.335). There were about 15% of male-male partnerships where both men were not protected against HPV. Interventions targeting vaccinated individuals to encourage their unvaccinated partners to be vaccinated might increase the HPV vaccine coverage.

Sexual mixing patterns among male-female partnerships in Melbourne, Australia

BACKGROUND

Individuals who have both opposite- and same-sex partners have the potential to pass sexually transmitted infections (STIs) between high- and low-risk populations. Our aim was to examine assortative sexual mixing in terms of same-sex activity among male-female partnerships.

METHODS

This was a retrospective repeated cross-sectional study of male-female partnerships attending the Melbourne Sexual Health Centre (MSHC) from 2015 to 2019. Sex of sexual partners was collected via computer-assisted self-interview. We calculated the proportion of partnerships where at least one individual reported same-sex partners in the previous 12months and the degree of assortativity by bisexuality.

RESULTS

A total of 2112 male-female partnerships (i.e. 4224 individuals) were included, with a median age of 27 years (IQR 23-31). Overall, 89.3% (1885/2112) of male-female partnerships did not report any other same-sex partners; however, in 9.5% (201/2112) of partnerships, same-sex partners were reported by one individual and in 1.2% (26/2112) of partnerships, both individuals reported same-sex partners. Bisexuality appeared to be slightly assortative in male-female partnerships (r=0.163, 95% CI: 0.150-0.176; P<0.001).

CONCLUSION

One in 10 individuals in male-female partnerships had at least one same-sex partner within the previous 12months. Individuals were minorly selective by bisexuality, suggesting the patterns of bisexual mixing in male-female partners are more variable and this may have a significant impact on STI transmission in heterosexual populations.

What Will It Take to End HIV in the United States? : A Comprehensive, Local-Level Modeling Study

BACKGROUND

The Ending the HIV Epidemic (EHE) initiative aims to reduce incident HIV infections by 90% over a span of 10 years. The intensity of interventions needed to achieve this for local epidemics is unclear.

OBJECTIVE

To estimate the effect of HIV interventions at the city level.

DESIGN

A compartmental model of city-level HIV transmission stratified by age, race, sex, and HIV risk factor was developed and calibrated.

SETTING

32 priority metropolitan statistical areas (MSAs).

PATIENTS

Simulated populations in each MSA.

INTERVENTION

Combinations of HIV testing and preexposure prophylaxis (PrEP) coverage among those at risk for HIV, plus viral suppression in persons with diagnosed HIV infection.

MEASUREMENTS

The primary outcome was the projected reduction in incident cases from 2020 to 2030.

RESULTS

Absent intervention, HIV incidence was projected to decrease by 19% across all 32 MSAs. Modest increases in testing (1.25-fold per year), PrEP coverage (5 percentage points), and viral suppression (10 percentage points) across the population could achieve reductions of 34% to 67% by 2030. Twenty-five percent PrEP coverage, testing twice a year on average, and 90% viral suppression among young Black and Hispanic men who have sex with men (MSM) achieved similar reductions (13% to 68%). Including all MSM and persons who inject drugs could reduce incidence by 48% to 90%. Thirteen of 32 MSAs could achieve greater than 90% reductions in HIV incidence with large-scale interventions that include heterosexuals. A web application with location-specific results is publicly available (www.jheem.org).

LIMITATION

The COVID-19 pandemic was not represented.

CONCLUSION

Large reductions in HIV incidence are achievable with substantial investment, but the EHE goals will be difficult to achieve in most locations. An interactive model that can help policymakers maximize the effect in their local environments is presented.

PRIMARY FUNDING SOURCE

National Institutes of Health.

International travel as risk factor for Chlamydia trachomatis infections among young heterosexuals attending a sexual health clinic in Melbourne, Australia, 2007 to 2017

BackgroundInternational travel is considered a risk factor for acquiring Chlamydia trachomatis; however, there are little empirical data to support this.AimTo examine the prevalence and risk factors for Chlamydia trachomatis infections among heterosexual international travellers (n = 28,786) attending the Melbourne Sexual Health Centre (MSHC), Australia, compared to Australian residents (n = 20,614).MethodsWe conducted a repeated cross-sectional study and analysed sexual behaviours and chlamydia positivity among heterosexual males and females aged ≤ 30 attending MSHC for the first time between January 2007 and February 2017. 'Travellers' were defined as individuals born outside of Australia who had resided in the country < 2 years. Associations between patient characteristics and chlamydia positivity were examined.ResultsChlamydia positivity was higher among travellers (11.2%) compared with Australian residents (8.5%; p < 0.001). Male travellers had higher chlamydia positivity (12.1%) than Australian males (9.3%; p < 0.001), as did female travellers (10.4%) compared with Australian females (7.7%; p < 0.001). Travellers had a higher mean number of sexual partners than Australian residents among males (5.7 vs 4.7; p < 0.001) and females (3.6 vs 3.2; p < 0.001). Travellers from the United Kingdom, Europe, Ireland and New Zealand accounted for 29.6%, 21%, 8.5% and 5.8% of C. trachomatis infections, respectively. Chlamydia in males and females was associated with younger age (≤ 25), inconsistent condom use, a higher number of sexual partners (≥ 4 partners) and being a traveller (p < 0.001).ConclusionsWe found that international travel is an independent risk factor for chlamydia among young heterosexual travellers in Australia, who should therefore be a target group for chlamydia prevention.

Comparing sexual behaviours and knowledge between domestic students and Chinese international students in Australia: findings from two cross-sectional studies

Few studies investigate sexual health among Chinese international students in Australia. We recruited domestic (n = 623) and Chinese international (n = 500) students for separate online surveys on sexual behaviours and knowledge. Samples were compared using Chi square, Fisher's exact and equality of medians tests. Domestic students were more likely than international students to have ever touched a partner's genitals (81% vs. 53%, p < 0.01), had oral sex (76% vs. 44%, p < 0.01), vaginal intercourse (67% vs. 41%, p < 0.01) and anal intercourse (31% vs. 6%, p < 0.01). Domestic students were younger when they first touched a partner's genitals (16 vs. 18 years, p < 0.01), had oral sex (17 vs. 18 years, p < 0.01) and vaginal intercourse (17 vs. 18 years, p < 0.01). Domestic students were less likely than Chinese international students to report only one lifetime partner for touching genitals (22% vs. 50%, p < 0.01), oral sex (25% vs. 55%, p < 0.01), vaginal intercourse (30% vs. 58%, p < 0.01) and anal intercourse (54% vs. 88%, p < 0.01). Domestic students were more likely than Chinese international students to use the oral contraceptive pill (48% vs. 16%, p < 0.01) and long-acting reversible contraceptives (19% vs. 1%, p < 0.01). Domestic students scored higher than international students on a contraception and chlamydia quiz (4/5 vs. 2/5, p < 0.01). Domestic and Chinese international students differed in sexual behaviours and knowledge highlighting the need for relevant sexual health promotion for both groups.

Prevalence of human papillomavirus in teenage heterosexual males following the implementation of female and male school-based vaccination in Australia: 2014-2017

BACKGROUND

Australia introduced a school-based human papillomavirus (HPV) vaccination program for females aged 12-13 years in 2007, with a three-year catch-up to age 26; and for boys aged 12-13 from 2013, with a two-year catch-up to age 15. This study aimed to compare the prevalence of penile HPV between teenage heterosexual males in cohorts eligible or non-eligible for the school-based male vaccination program.

METHODS

Between 2014 and 2017, sexually active heterosexual males aged 17-19 were recruited from sexual health centres and community sources across Australia. Males provided a self-collected penile swab for 37 HPV genotypes using Roche Linear Array and completed a questionnaire. We calculated adjusted prevalence ratios (aPR) of HPV between males in two periods: 2014-2015 (preceding implementation of school-based male vaccination) and 2016-2017 (eligible for school-based male vaccination). Self-reported vaccine doses were confirmed with doses reported to the National HPV Vaccination Program Register.

RESULTS

Overall, 152 males were recruited in 2014-2015 and 146 in 2016-2017. Numbers of female sex partners and condom use did not differ between the two periods. The prevalence of quadrivalent vaccine-preventable [4vHPV] genotypes (6/11/16/18) was low in both periods (2.6% [2014-15] versus 0.7% [2016-17]; p = 0.371; aPR 0.28 [95% CI: 0.03-2.62]). Compared with men in 2014-2015, men in 2016-2017 had a lower prevalence of any of the 37 HPV genotypes tested (21.7% versus 11.6%; aPR 0.62 [95% CI: 0.36-1.07]) and any of the 13 high-risk genotypes tested (15.8% versus 7.5%; aPR 0.59 [95% CI: 0.30-1.19]). Prevalence of low-risk HPV genotypes did not differ between the two periods. Of the males recruited in 2016-2017, 55% had received ≥1 vaccine dose.

CONCLUSION

The prevalence of 4vHPV genotypes among teenage heterosexual males in both cohorts was low, presumably due to herd protection from the female-only vaccination program. Further studies are required to determine the impact of universal HPV vaccination on HPV prevalence in males.

Inferring the age difference in HIV transmission pairs by applying phylogenetic methods on the HIV transmission network of the Swiss HIV Cohort Study

Age-mixing patterns are of key importance for understanding the dynamics of human immunodeficiency virus (HIV)-epidemics and target public health interventions. We use the densely sampled Swiss HIV Cohort Study (SHCS) resistance database to study the age difference at infection in HIV transmission pairs using phylogenetic methods. In addition, we investigate whether the mean age difference of pairs in the phylogenetic tree is influenced by sampling as well as by additional distance thresholds for including pairs. HIV-1 pol-sequences of 11,922 SHCS patients and approximately 240,000 Los Alamos background sequences were used to build a phylogenetic tree. Using this tree, 100 per cent down to 1 per cent of the tips were sampled repeatedly to generate pruned trees (N = 500 for each sample proportion), of which pairs of SHCS patients were extracted. The mean of the absolute age differences of the pairs, measured as the absolute difference of the birth years, was analyzed with respect to this sample proportion and a distance criterion for inclusion of the pairs. In addition, the transmission groups men having sex with men (MSM), intravenous drug users (IDU), and heterosexuals (HET) were analyzed separately. Considering the tree with all 11,922 SHCS patients, 2,991 pairs could be extracted, with 954 (31.9 per cent) MSM-pairs, 635 (21.2 per cent) HET-pairs, 414 (13.8 per cent) IDU-pairs, and 352 (11.8 per cent) HET/IDU-pairs. For all transmission groups, the age difference at infection was significantly (P < 0.001) smaller for pairs in the tree compared with randomly assigned pairs, meaning that patients of similar age are more likely to be pairs. The mean age difference in the phylogenetic analysis, using a fixed distance of 0.05, was 9.2, 9.0, 7.3 and 5.6 years for MSM-, HET-, HET/IDU-, and IDU-pairs, respectively. Decreasing the cophenetic distance threshold from 0.05 to 0.01 significantly decreased the mean age difference. Similarly, repeated sampling of 100 per cent down to 1 per cent of the tips revealed an increased age difference at lower sample proportions. HIV-transmission is age-assortative, but the age difference of transmission pairs detected by phylogenetic analyses depends on both sampling proportion and distance criterion. The mean age difference decreases when using more conservative distance thresholds, implying an underestimation of age-assortativity when using liberal distance criteria. Similarly, overestimation of the mean age difference occurs for pairs from sparsely sampled trees, as it is often the case in sub-Saharan Africa.

Incident HIV infection has fallen rapidly in men who have sex with men in Melbourne, Australia (2013-2017) but not in the newly-arrived Asian-born

Background

We examined differences in incident HIV infection between newly-arrived Asian-born and other men who have sex with men (MSM) after the introduction of universal HIV treatment guidelines in 2015 and pre-exposure prophylaxis in 2016.

Methods

Clinical, demographic, laboratory and behavioural data on MSM presenting for HIV testing at the Melbourne Sexual Health Centre from July 2013 to June 2017 were extracted. We compared the proportion of newly-arrived (four years or less in Australia), Asian-born and other MSM tested each year who were diagnosed with incident HIV infection (negative test within one year or diagnosis with indeterminate or negative Western Blot).

Results

We analysed 35,743 testing episodes in 12,180 MSM, including 2781 testing episodes in 1047 newly-arrived Asian-born MSM. The proportion of other MSM tested each year who were diagnosed with incident HIV infection fell from 0.83% in 2014 to 0.38% in 2017 (p = .001), but did not fall in newly-arrived Asian-born MSM (from 1.18% in 2014 to 1.56% in 2017, p = .76). In the multivariate logistic regression, in 2016/2017 but not in 2014/2015, being newly-arrived Asian-born was associated with an increased odds of diagnosis of incident HIV infection (aOR 3.29, 95%CI 1.82–5.94, p < .001).

Conclusions

The epidemiology of HIV in Melbourne Australia has changed dramatically. While there has been an overall reduction amongst MSM, the incidence of HIV in newly-arrived Asian-born MSM remains high. Failing to address these new inequalities leaves individuals at risk and may offset the population benefit of biomedical HIV prevention.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3325-0) contains supplementary material, which is available to authorized users.

Human papillomavirus vaccination and the role of herd effects in future cancer control planning: a review

INTRODUCTION

Vaccine herd effects are the indirect protection that vaccinated persons provide to those who remain susceptible to infection, due to the reduced transmission of infections. Herd effects have been an important part of the discourse on how to best implement human papillomavirus (HPV) vaccines and prevent HPV-related diseases.

AREAS COVERED

In this paper, we review the theory of HPV vaccine herd effects derived from mathematical models, give an account of observed HPV vaccine herd effects worldwide, and examine the implications of vaccine herd effects for future cervical cancer screening efforts.

EXPERT COMMENTARY

HPV vaccine herd effects improve the cost-effectiveness of vaccinating preadolescent girls, but contribute to making gender-neutral vaccination less economically efficient. Vaccination coverage and sexual mixing patterns by age are strong determinants of herd effects. Many countries worldwide are starting to observe reductions in HPV-related outcomes likely attributable to herd effects, most notably declining anogenital warts in young men, and declining HPV-16/18 infection prevalence in young unvaccinated women. Policy makers making recommendations for cervical cancer screening will have to consider HPV vaccination coverage and herd effects, as these will affect the positive predictive value of screening and the risk of cervical cancer in unvaccinated women.

Early sexual experiences of teenage heterosexual males in Australia: a cross-sectional survey

OBJECTIVE

There are limited data on the patterns of early sexual behaviours among Australian teenage heterosexual boys. This study describes the nature and onset of early sexual experiences in this population through a cross-sectional survey.

DESIGN

A cross-sectional survey between 2014 and 2015 SETTING: Major sexual health clinics and community sources across Australia PARTICIPANTS: Heterosexual men aged 17-19 years RESULTS: There were 191 men in the study with a median age of 19.1 years. Median age at first oral sex was 16.4 years (IQR: 15.5-17.7) and 16.9 years (IQR: 16.0-18.0) for first vaginal sex. Most men had engaged in oral sex (89.5%) and vaginal sex (91.6%) in the previous 12 months with 32.6% reporting condom use at last vaginal sex. Of the total lifetime female partners for vaginal sex reported by men as a group (n=1187): 54.3% (n=645) were the same age as the man, 28.3% (n=336) were a year or more younger and 17.4% (n=206) were a year or more older. Prior anal sex with females was reported by 22% with 47% reporting condom use at last anal sex. Median age at first anal sex was 18.2 years (IQR: 17.3-18.8). Anal sex with a female was associated with having five or more lifetime female sexual partners for oral and vaginal sex.

CONCLUSIONS

These data provide insights into the trajectory of sexual behaviours experienced by teenage heterosexual boys following sexual debut, findings which can inform programme promoting sexual health among teenage boys.