Sexual networks: implications for the transmission of sexually transmitted infections

The structures of sexual networks are essential for understanding the dynamics of sexually transmitted infections. Standard epidemiological models largely disregard the complex patterns of intimate contacts. Social network analysis offers important insight into how to conceptualize and model social interaction and has the potential to greatly enhance the understanding of disease epidemics.     

Expression of structural proteins in human female and male genital epithelia and implications for sexually transmitted infections

Men and women differ in their susceptibility to sexually transmittable infections (STIs) such as human immunodeficiency virus (HIV). However, a paucity of published information regarding the tissue structure of the human genital tract has limited our understanding of these gender differences. We collected cervical, vaginal, and penile tissues from human adult donors. Tissues were prepared with hematoxylin and eosin stains or immunofluorescence labeling of epithelial cell proteins and were analyzed for structural characteristics. Rhesus macaque genital tissues were evaluated to assess the use of this model for HIV/simian immunodeficiency virus transmission events. We found the stratified squamous epithelia of the male and female genital tract shared many similarities and important distinctions. Expression of E-cadherins, desmogleins 1/2, and involucrin was seen in all squamous epithelia, though expression patterns were heterogeneous. Filaggrin and a true cornified layer were markedly absent in female tissues but were clearly seen in all male epithelia. Desmogleins 1/2 were more consistent in the outermost strata of female squamous genital epithelia. Macaque tissues were similar to their respective human tissues. These initial observations highlight how male and female genital epithelia resemble and differ from one another. Further information regarding tissue structural characteristics will help to understand how STIs traverse these barriers to cause infection. This knowledge will be essential in future HIV pathogenesis, transmission, and prevention studies.     

Male circumcision and sexually transmitted infections in Botswana

This study set out to investigate the influence of male circumcision and other factors on sexually transmitted infections in Botswana. A syndromic approach, which diagnoses a sexually transmitted infection based on the presence of urethral discharge or genital ulcers rather than on laboratory tests, was used. The data were from the 2001 Botswana AIDS Impact Survey where a nationally representative, randomly selected sample of men and women aged 10-64 years were interviewed in both urban and rural areas. The sample selected for this study consisted of 216,480 men aged 15-64 years who had ever had sexual intercourse. The logistic regression technique was executed to examine the association between male circumcision and self-reported urethral discharge or genital ulcers, while controlling for all other independent variables in the analysis. The main finding of this study was that among men who are circumcised, the odds for self-reported urethral discharge or genital ulcers are significantly lower than for those men who are not circumcised in both urban and rural Botswana. The analysis also showed that the odds in favour of self-reported urethral discharge or genital ulcers, for men who drink alcohol, are twice as large as those for men who do not drink alcohol, controlling for all other independent variables in the analysis. Religion and ethnicity also came through as factors exerting a protective influence against self-reported symptoms of sexually transmitted infections. The conclusion is that while male circumcision appears to be significantly associated with the risk for self-reported urethral discharge or genital ulcers, it is man's behaviour, irrespective of ethnicity or religious dictates, that continues to play a vital role in protection against self-reported symptoms of sexually transmitted infections in Botswana.     

Antagonistic coevolution between hosts and sexually transmitted infections

Sexually transmitted infections (STIs) are predicted to play an important role in the evolution of host mating strategies, and vice versa, yet our understanding of host-STI coevolution is limited. Previous theoretical work has shown mate choice can evolve to prevent runaway STI virulence evolution in chronic, sterilizing infections. Here, I generalize this theory to examine how a broader range of life-history traits influence coevolution; specifically, how host preferences for healthy mates and STI virulence coevolve when infections are acute and can cause mortality or sterility, and hosts do not form long-term sexual partnerships. I show that mate choice reduces both mortality and sterility virulence, with qualitatively different outcomes depending on the mode of virulence, costs associated with mate choice, recovery rates, and host lifespan. For example, fluctuating selection—a key finding in previous work—is most likely when hosts have moderate lifespans, STIs cause sterility and long infections, and costs of mate choice are low. The results reveal new insights into the coevolution of mate choice and STI virulence as different life-history traits vary, providing increased support for parasite-mediated sexual selection as a potential driver of host mate choice, and mate choice as a constraint on the evolution of virulence.     

Use of the Internet for the surveillance and prevention of sexually transmitted diseases

The Internet is a relatively new tool in the surveillance and prevention of sexually transmitted infections, and this review examines its global use in this regard. Much use has been made in the form of information collection and dissemination; targeted population engagement through chat rooms, partner notification and other mechanisms; and the provision of testing services and other products. Internet users may need education concerning reputable websites, and public health practitioners need proficiency in the use of social media and marketing.     

The diaphragm and lubricant gel for prevention of cervical sexually transmitted infections: results of a randomized controlled trial

Background

We evaluated the effectiveness of the Ortho All-Flex Diaphragm, lubricant gel (Replens®) and condoms compared to condoms alone on the incidence of chlamydial and gonococcal infections in an open-label randomized controlled trial among women at risk of HIV/STI infections.

Methods

We randomized 5045 sexually-active women at three sites in Southern Africa. Participants who tested positive for curable STIs were treated prior to enrollment as per local guidelines. Women were followed quarterly and tested for Chlamydia trachomatis (CT) or Neisseria gonorrhoeae (GC) infection by nucleic-acid amplification testing (Roche Amplicor®) using first-catch urine specimens. STIs detected at follow-up visits were treated. We compared the incidence of first infection after randomization between study arms in both intent-to-treat (ITT) and per-protocol populations.

Findings

Baseline demographic, behavioral and clinical characteristics were balanced across study arms. Nearly 80% of participants were under 35 years of age. Median follow-up time was 21 months and the retention rate was over 93%. There were 471 first chlamydia infections, 247 in the intervention arm and 224 in the control arm with an overall incidence of 6.2/100 woman-years (wy) (relative hazard (RH) 1.11, 95% Confidence Interval (CI): 0.93–1.33; p = 0.25) and 192 first gonococcal infections, 95 in the intervention arm and 97 in the control arm with an overall incidence of 2.4/100wy (RH 0.98, 95%CI: 0.74–1.30; p = 0.90). Per protocol results indicated that when diaphragm adherence was defined as “always use” since the last visit, there was a significant reduction in the incidence of GC infection among women randomized to the intervention arm (RH 0.61, 95%CI: 0.41–0.91, P = 0.02).

Interpretation

There was no difference by study arm in the rate of acquisition of CT or GC. However, our per-protocol results suggest that consistent use of the diaphragm may reduce acquisition of GC.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00121459","term_id":"NCT00121459"}}NCT00121459 [{"type":"clinical-trial","attrs":{"text":"NCT00121459","term_id":"NCT00121459"}}NCT00121459]     

Epidemiology of sexually transmitted Chlamydia trachomatis infections in male patients

868 male urethritis patients were studied for the presence of chlamydiae in the 1981-1986 period. 36% of NGU, 31.3% of gonococcal urethritis and 58.8% of PGU urethritis patients presented C. trachomatis infections as detected by cell culture inoculation. Chlamydial infection was recorded more often in the 21-30 years age group (30.8%), in unmarried patients (70.6%), as well as in people with low educational degree (46.6% of cases), 42.3% of the C. trachomatis cases were already confronted with one or more urethritis episodes. 24.7% of patients have been subjected to a previous antichlamydial treatment.     

Modelling the impact of correlations between condom use and sexual contact pattern on the dynamics of sexually transmitted infections

Background

It is believed that sexually active people, i.e. people having multiple or concurrent sexual partners, are at a high risk of sexually transmitted infections (STI), but they are likely to be more aware of the risk and may exhibit greater fraction of the use of condom. The purpose of the present study is to examine the correlation between condom use and sexual contact pattern and clarify its impact on the transmission dynamics of STIs using a mathematical model.

Methods

The definition of sexual contact pattern can be broad, but we focus on two specific aspects: (i) type of partnership (i.e. steady or casual partnership) and (ii) existence of concurrency (i.e. with single or multiple partners). Systematic review and meta-analysis of published studies are performed, analysing literature that epidemiologically examined the relationship between condom use and sexual contact pattern. Subsequently, we employ an epidemiological model and compute the reproduction number that accounts for with and without concurrency so that the corresponding coverage of condom use and its correlation with existence of concurrency can be explicitly investigated using the mathematical model. Combining the model with parameters estimated from the meta-analysis along with other assumed parameters, the impact of varying the proportion of population with multiple partners on the reproduction number is examined.

Results

Based on systematic review, we show that a greater number of people used condoms during sexual contact with casual partners than with steady partners. Furthermore, people with multiple partners use condoms more frequently than people with a single partner alone. Our mathematical model revealed a positive relationship between the effective reproduction number and the proportion of people with multiple partners. Nevertheless, the association was reversed to be negative by employing a slightly greater value of the relative risk of condom use for people with multiple partners than that empirically estimated.

Conclusions

Depending on the correlation between condom use and the existence of concurrency, association between the proportion of people with multiple partners and the reproduction number can be reversed, suggesting the sexually active population is not necessary a primary target population to encourage condom use (i.e., sexually less active individuals could equivalently be a target in some cases).

     

Sexual partners,sexually transmitted infections,and prostate cancer risk

Background: The etiology of prostate cancer (PCa) is poorly understood. Sexual activity and sexually transmitted infections (STIs) are among factors under scrutiny, with controversial findings to date. Methods: We examined the association between the number and gender of sexual partners, STIs and PCa risk in the context of PROtEuS, a population-based case–control study set amongst the mainly French-speaking population in Montreal, Canada. The study included 1590 histologically-confirmed PCa cases diagnosed in a Montreal French hospital between 2005 and 2009, and 1618 population controls ascertained from the French electoral list, Montreal residents, frequency-matched to cases by age. In-person interviews elicited information on sociodemographic, lifestyle and environmental factors. Unconditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) between sexually related factors and PCa risk, adjusting for age, ancestry, family history of PCa, and PCa screening history. Results: Subjects with more than 20 sexual partners in their lifetime had a decreased risk of PCa (OR 0.78, 95% CI 0.61–1.00) as did subjects who specifically had more than 20 female sexual partners (OR 0.72, 95% CI 0.56–0.94). By contrast, having had several male sexual partners appeared to confer some excess in risk of PCa. No association emerged for history of STIs and PCa but STIs prevalence was low. Conclusion: Our findings are in support of a role for the number of sexual partners in PCa development. The gender of sexual partners should be taken into account in future studies investigating this association.     

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 (C(c)) 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 C(c) values for GC and CT, while C(c) 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.     

Laboratory diagnosis of sexually transmitted infections in chronic inflammatory diseases of the reproductive system

The complex clinico-laboratory examination of 120 infertile married couples and 120 couples with habitual miscarriage was made. For control, 96 healthy married couples were used. The microbiological risk factors of chronic pelvic inflammatory diseases were determined, namely: mixed parasitocenosis, including active anaerobic, viral and fungal components, as well as Chlamydia trachomatis. As shown in this study, metabolically active forms of chlamydial infection were characteristic of infertile married women and persistent forms of C. trachomatis, for pregnant women. At the same time chlamydial infection did not cause infertility in males. The use two of levels of laboratory tests for qualitative, quantitative and functional evaluation of parasitocenoses were proposed.     

Morbidity in sexually transmitted infections in the Republic of North Ossetia-Alania and the improvement of epidemiological surveillance

The present situation in sexually transmitted diseases (STD) in the Republic of North Ossetia-Alania is characterized as unfavorable. Morbidity in different nosological forms has been found to show different tendencies. The causes of elevated morbidity in STD observed in recent years have social, economic, psychological, ethical and moral, rather than medical character. The main trends in the improvement of epidemiological surveillance on STD have been determined.     

A cognitive behavioural intervention to reduce sexually transmitted infections among gay men: randomised trial

ObjectiveTo determine the effectiveness of a brief cognitive behavioural intervention in reducing the incidence of sexually transmitted infections among gay men.DesignRandomised controlled trial with 12 months'' follow up.SettingSexual health clinic in London.Participants343 gay men with an acute sexually transmitted infection or who reported having had unprotected anal intercourse in the past year.Results72% (361/499) of men invited to enter the study did so. 90% (308/343) of participants returned at least one follow up questionnaire or re-attended the clinic and requested a check up for sexually transmitted infections during follow up. At baseline, 37% (63/172) of the intervention group and 30% (50/166) of the control group reported having had unprotected anal intercourse in the past month. At 12 months, the proportions were 27% (31/114) and 32% ( 39/124) respectively (P=0.56). However, 31% (38/123) of the intervention group and 21% (35/168) of controls had had at least one new infection diagnosed at the clinic (adjusted odds ratio 1.66, 95% confidence interval 1.00 to 2.74). Considering only men who requested a check up for sexually transmitted infections, the proportion diagnosed with a new infection was 58% (53/91) for men in the intervention group and 43% (35/81) for men in the control group (adjusted odds ratio 1.84, 0.99 to 3.40). Using a regional database that includes information from 23 sexual health clinics in London, we determined that few participants had attended other sexual health clinics.ConclusionsThis behavioural intervention was acceptable and feasible to deliver, but it did not reduce the risk of acquiring a new sexually transmitted infection among these gay men at high risk. Even carefully designed interventions should not be assumed to bring benefit. It is important to evaluate their effects in randomised trials with objective clinical end points.

What is already known on this topic

The need for effective HIV prevention strategies based on reducing sexual risk behaviour remains importantFew interventions to reduce sexual risk behaviour have been rigorously evaluated using randomised controlled trials

What this study adds

This is the first randomised controlled trial of an intervention addressing sexual behaviour in homosexual men that uses sexually transmitted infections and self reported behaviour as end pointsThe intervention was brief and feasible to use in a busy clinic, but it did not reduce the risk of participants acquiring new infectionsThe potential for behavioural interventions to do more harm than good needs to be taken seriously     

Sex-specific immunization for sexually transmitted infections such as human papillomavirus: insights from mathematical models

Background

Sex-specific differences regarding the transmissibility and the course of infection are the rule rather than the exception in the epidemiology of sexually transmitted infections (STIs). Human papillomavirus (HPV) provides an example: disease outcomes differ between men and women, as does the potential for transmission to the opposite sex. HPV vaccination of preadolescent girls was recently introduced in many countries, and inclusion of boys in the vaccination programs is being discussed. Here, we address the question of whether vaccinating females only, males only, or both sexes is the most effective strategy to reduce the population prevalence of an STI like HPV.

Methods and Findings

We use a range of two-sex transmission models with varying detail to identify general criteria for allocating a prophylactic vaccine between both sexes. The most effective reduction in the population prevalence of infection is always achieved by single-sex vaccination; vaccinating the sex with the highest prevaccine prevalence is the preferred strategy in most circumstances. Exceptions arise only when the higher prevaccine prevalence is due to a substantially lower rate of natural immunity, or when natural immunity is lifelong, and a prolonged duration of infectiousness coincides with increased transmissibility. Predictions from simple models were confirmed in simulations based on an elaborate HPV transmission model. Our analysis suggests that relatively inefficient genital transmission from males to females might render male vaccination more effective in reducing overall infection levels. However, most existing HPV vaccination programs have achieved sufficient coverage to continue with female-only vaccination.

Conclusions

Increasing vaccine uptake among preadolescent girls is more effective in reducing HPV infection than including boys in existing vaccination programs. As a rule, directing prophylactic immunization at the sex with the highest prevaccine prevalence results in the largest reduction of the population prevalence. Please see later in the article for the Editors'' Summary