Although HIV prevalence is decreasing , the drivers of ongoing HIV infections are yet to be addressed in more detail. The preventative utility of co-factors (STIs, intravaginal practices, intimate partner violence) seems unclear and biological HIV transmission risk remains crucial among MSM [3, 6, 7, 20]. In this study, dyspareunia and signs of anogenital epithelial trauma were highly prevalent in FSWs and MSM, indicating considerable limitations to sexual health and personal well-being. Exposure to blood during sexual encounters may increase HIV infection risk as evidenced by previous research [12, 19]. Vaginal coital bleeding in this study was more prevalent than previously described [9–11], and direct signs of anal bleeding were rife among MSM, justifying the need for further aetiological analysis for possible prevention measures.
Steady sexual relationships alongside sex work were common, which implies the importance of regular partner testing or considering pre-exposure prophylaxis given that HIV infections within heterosexual regular partnerships and unions classically outweigh the burden of HIV infections through every other mode of exposure in Kenya . Artificial lubricant use was moderately popular with FSWs, indicating a possible benefit of lubricants for vaginal intercourse, confirmed by the sex workers' favourable assessment of lubricants as a remedy against dyspareunia. Lubricants, in combination with condoms, have been recommended for MSM  and have found high acceptance with Black American women . Uptake of lubricants for anal sex is regularly promoted by Hoymas for MSM in Kenya. Lubricants are included in the package of services provided for MSM during a visit. Intravaginal substance insertion was common in the FSW sample and linked to an increased risk of living with HIV, yet the effect was small, and the large-scale impact of intravaginal practices as a driver of the HIV pandemic seems limited according to meta-analyses . Painkillers and sedatives were reported to be used in moderation but alcohol use was very common among the sex workers and this may be a possible risk factor for HIV transmission due to reduced self-care and precaution measures under the influence of alcohol. Alternatively, drinking and drug use may be a self-treatment for dyspareunia, and thus the association between living with HIV and sex drug or alcohol use may in turn be mediated via the infection risk from epithelial disruption linked to painful intercourse.
Contrary to the hypothesis that longer sexual abstinence breaks may subsequently lead to HIV acquisition, longer abstinence in the previous month was positively associated with living without HIV among FSWs. This may be due to life-long tendencies of reduced numbers of clients and continuously rare sexual contacts with them for some participants living without HIV. Some sex workers living with HIV may, in turn, have taken fewer abstinence breaks between clients recently, which, however, may not reflect their abstinence intervals at the time around their actual HIV infection as participants had contracted HIV earlier than the previous month. For the longest abstinence gaps in adult life from memory, there was no significant association with HIV status, neither among FSWs nor MSM, so the association with abstinence remains unclear. Determining the exact role of abstinence intervals for HIV acquisition would require determining abstinence behaviour at the time of the actual HIV acquisition in the past, which was an impossible task within this cross-sectional approach. Therefore, a lack of significant associations between longest memorized abstinence gaps in adult life and HIV status may not necessarily contradict the hypothesis of shorter abstinence gaps or higher intercourse regularity as protective against HIV acquisition. Nonetheless, we could not establish any confirmatory relationships between higher memorized maximum abstinence intervals and HIV infection risk. Studies confirming such a putative link may be difficult to set up and may involve only assuredly early stage or acute HIV infections, at a time when participants can still remember their exact sexual behaviour and sex frequencies in previous weeks or months. The potential transmission risk factor of longer abstinence periods may be regarded as innately elusive in this respect, yet with some conceptual and empirical plausibility from the theoretical background the study was based on.
We found that later sexual debut may protect against HIV infection, which is somewhat intuitive. The apparent protection against HIV acquisition by having anonymous partners and by longer intercourse duration that is implied by the cross-sectional significant associations with HIV status is not clear and needs further exploration. While FSWs agreed that longer duration of intercourse may increase discomfort, it may also be the case that distensible vaginal epithelial lining naturally protects against HIV transmission through less disruption and concomitantly allows for longer intercourse sessions. The apparent protection against HIV infection by foreplay may similarly be explained by more relaxed tissues and better lubrication and hence less epithelial trauma, reducing the efficiency of HIV infection.
The hypothesis linking sexual dysfunction and epithelial trauma signs to HIV infection status was confirmed in so far as dyspareunia levels and frequency, as well as epithelial trauma signs, were positively associated with living with HIV among FSWs. The temporal direction and causal relevance of this suggested link remains debatable given the cross-sectional study design, and further investigation is needed. The more general relationship satisfaction item (ii) was the only item of the dyspareunia score without a significant association with self-reported HIV status in the FSW sample; and general satisfaction with sexual life (item (iii)) turned out to be significantly higher in FSWs living with HIV than in those living without HIV. All other sexual dysfunction score items showed the same direction of association. The differences between the means of the individual score values, however, were small as were standardized effect sizes. When items of unidirectional differences from the score were combined, however, a small to medium standardized effect size of 0.29 was reached, e.g., for items (iv)-(viii). The relevance and utility of this cluster of subjective complaints and epithelial trauma signs for HIV risk will need to be determined by further study.
The subjective assessment of dyspareunia factors by FSWs may imply modes of prevention for further investigation. Steady partnerships seem to be beneficial as FSWs highly agreed that discomfort occurs less with a steady partner than with casual ones. Whatever their protective mechanism, they are difficult to maintain for FSWs and other people who are promiscuous or unable to enter steady relationships or living in social contexts favouring concurrency. As for more experience with sex partners and having several partners at once, no clear recommendation can be drawn from the sex workers' assessment for the prevention of dyspareunia. Longer duration of intercourse may worsen discomfort so that extremely prolonged sex may be recommended against although the bivariate analysis suggested the opposite effect of sex duration regarding the odds of living with HIV (see above). Higher regularity of intercourse, foreplay and lubricant use may be considered as protective as the women agreed that these factors may ease sexual dysfunction. The ideal maximum abstinence gaps between receptive sex appear unclear at the time of writing, and further investigation is needed. Interviewer and confirmation bias cannot be ruled out for the consensus of sex regularity as preventing painful intercourse, and blinded interviewing in further studies may be advisable to corroborate or refute the links to HIV risk and overall sexual health. Condoms seem not to interfere as most women judged their effect on dyspareunia to be irrelevant, so their role as an effective means to HIV prevention may be upheld. Finally, alcohol or sedative and analgesics use may increase HIV infection risk as seen in the inferential statistics, and there was no subjective agreement that drugs or alcohol would ease dyspareunia in any way.
Limitations of the study
The study revealed significant associations among FSWs for known HIV risk-taking behaviour such as early sexual debut, intravaginal substance insertion, alcohol and drug use as well as for the new links between sexual dysfunction variables and HIV serostatus. The latter, however, was self-reported, which helped establish a trusting relationship with participants but brought less reliability and objectivity for the HIV status variable. Among MSM, who also self-reported HIV status and were interviewed in the same fashion as sex workers, no similar significant results were found for anal dyspareunia. This difference may be due to more pronounced variation in the extent of vaginal sexual dysfunction in the sample because of higher variability of disorders of lubrication, arousal, and of psychological confounding factors, because of physiological vaginal variation, co-infections or bacterial vaginosis. Gynaecological or rectal examinations and laboratory tests were not performed, which further limits the validity of these findings, especially since the implication of epithelial disruption by painful intercourse or perceived discomfort was largely conceptual. The Nairobi population is culturally and ethnically diverse, and the role of genetics and different ethnic traits would need to be taken into consideration in further studies. Differences in vaginal anatomy were found between African-American and white women , and Frank Plummer had observed in his early HIV immunity research that many highly exposed persistently seronegative FSWs were related to one another . As for anal HIV transmission risk, matters of anatomy and physiology may be of a more uniform nature so that differences in anal epithelial disruption may be more elusive and harder to differentiate in a sample because related complaints and signs may in turn be more uniform among MSM than among heterosexual women. Other psychological, medical, and behavioural factors may also play a role for sexual dysfunctions and minor epithelial trauma in MSM, including general anorectal health factors. These were hard to represent and differentiate with a cross-sectional, questionnaire-based study design.
The significant relationship between direct and indirect signs of epithelial disruption and self-reported HIV infection status, as well as the FSWs' majority assessment on sex regularity as alleviating painful intercourse, may partly be due to interviewer or confirmation bias. Interviewer-blinded ways of data collection should be aimed at in future investigations using similar sexual dysfunction scores for the validation of an associated HIV infection risk. Although various classical HIV risk-taking behaviours and medical factors, such as early sexual debut, other STIs and intravaginal practices, were analysed in this study and yielded significant associations, their standardized effect sizes were lower than some of the more novel dyspareunia and epithelial disruption sign variables. Their confounding effects and those of the novel factors presented have to be evaluated in a multivariate logistic regression analysis, which was not done in this early stage cross-sectional study. The same holds true for cross-links between sedative or analgesic drug use and painful intercourse for establishing independent relationships of these factors with HIV infection status. The aim of the current study was to search for preliminary evidence for a novel factor that carried empirical and conceptual plausibility from previous HIV immunity and sexual health research. For this reason, direct implications for HIV prevention science, let alone preventive interventions, are highly limited. The results and relationships established nonetheless justify further investigations and refinements regarding the epithelial disruption signs and sexual dysfunction scores and their association with HIV infection status or HIV acquisition.