There is no question that sexually transmitted infections (STIs) are primarily a health issue of young people, both in terms of incidence and health sequelae. However, the population globally is ageing and rapidly increasing numbers of people are living long, healthy and potentially sexually active lives. In recent years, there has been a focus on the need to recognise sexuality and sexual health needs as important components of older people's lives. Studies of middle aged and older women consistently report that sexual relations are important to women in these age groups [1,2]. A reluctance by health professionals and aged care services to acknowledge these needs has been highlighted [3,4]. Despite the growing discussion around the recognition of sexuality and sexual activity in older age, there is limited research available on rates and patterns of sexual practices and STIs in this demographic [5,6]. The published literature is sparse and heterogeneous, with few longitudinal studies of STIs among women older than 45 years, in particular.
The WHO generally has reported HIV rates in adults only up to 49 years of age . Some national health agencies do not provide stratified STI data beyond 45 years of age, potentially missing important variations in STI rates within the last three to four decades of life [8,9]. Many national STI and sexuality surveys [10,11] concentrate mainly on younger populations, with the UK National Surveys of Sexual Attitudes and Lifestyles only recently increasing the age cutoff from 44 years . In light of this, many questions remain. First, it is uncertain whether STI rates are indeed increasing in older populations, or increasing diagnoses are simply due to an expanding denominator. Second, little is known about whether specific high-risk sub-groups of older people, such as gay men, experience higher rates. Third, there have been few studies of whether sexual risk behaviours in older people have changed over time. Finally it is not known whether older people are biologically more or less susceptible to acquiring STIs than their younger counterparts. This review examines the available literature on sexual behaviour and STIs among older populations. We have defined ‘older’ as including populations of people 45 years of age or older. As there is variability in the lower age cutoffs between studies, the lower limit of age for each study is reported. New diagnoses of STIs rather than chronic or persisting infection (for instance HIV or syphilis acquired at a younger age) are examined.
OVERVIEW OF RATES OF SEXUALLY TRANSMITTED INFECTIONS OTHER THAN HIV BY AGE GROUPS
Surveillance data from the United Kingdom on STI diagnoses in genitourinary medicine (GUM) clinics and community settings from 2008 to 2010  report specific STI rates in older populations by sex, only as ‘45+’. There was virtually no change in rates of STIs in people older than 45 years from 2008 to 2010. In this age group, chlamydia rates were 170-fold higher and gonorrhoea rates 24-fold higher in the 20–24 age group. Despite these huge differences in rates, it is important to note that there were more than 5000 new diagnoses of chlamydia and gonorrhoea in 2010 in this age group. For males, rates of newly diagnosed syphilis were much more similar with rates approximately three-fold higher in young men. However in women, rates in the young were 20 times more common than in those aged 45 years or older. There was an increase in rates of first episode of ano-genital warts from 2002 to 2010 in both sexes in those aged 45–64 and among those aged 65 years and older. As with the bacterial STIs, the disease burden was much lower than in younger age groups, with the highest rates in the older age groups being among men aged 45–64 years (45.5 per 100 000) . Rates in 20–24 year old men were about 17 times higher. Earlier studies in the United Kingdom of GUM attendees aged greater than 45 years reported the rate of STIs more than doubling in 2003 compared with 1996, the biggest increase being seen in the 55–59 years age group. However, this group comprised only 4% of all GUM attendees . It is plausible that increased testing and improved sensitivity of diagnostic tests may have led to the increase in notifications, but the potential contribution of an increase in riskier sexual practices among this age group cannot be ruled out. In a small study at two London GUM clinics, attendance of women aged 46 years and over quadrupled from 1998 to 2008, however the proportion of acute STIs in this age group remained stable over time [12▪].
Other countries, such as the United States, Canada and Australia, have seen a similar increase in STI diagnoses in men and women over the past decade. In Australia, among women for instance, the rate of chlamydia has more than tripled. This increase has been reported across all age groups, including those older than 50 years. In 2011, the rates of chlamydia in women older than 65 years were 1.5 per 100 000, compared with 2181 per 100 000 in women aged 20–24 years . The overall numbers of new diagnoses in men and women aged 50–59 years and aged 60 years and older, though still low, increased from 2006 to 2010 for gonorrhoea, chlamydia and syphilis (men only) . In the United States, an increase in STI diagnoses from 2006 to 2010 saw the chlamydia rate in men increase by 36.4%, compared with a 19.5% increase in women during this period. Rates of new diagnoses of chlamydia have remained fairly constant in those aged 55–64 years and those 65 years and older (9.3 per 100 000 and 2.1 per 100 000 in women, 10.9 per 100 000 and 2.8 per 100 000 in men, respectively, in 2010). In contrast, the rate of chlamydia was over 3400 per 100 000 women aged 20–24 years in 2010. Similar trends and differences between age groups were reported for gonorrhoea. For men aged between 55 and 64 years, rates of newly diagnosed syphilis were more similar with rates approximately eight-fold higher in young men. However in women, rates in the young were 22 times more common than in those aged 55–64 . In a cross-sectional cohort study of 541 HIV-infected people conducted in the United States in 2008, overall STI prevalence was 3% among people older than 50, compared with 11% in those aged 18–35 years, demonstrating that STIs continue to be identified at all age groups . In Canada, data from British Columbia were collated in slightly younger age groups of 40–59 years and 60 years or older. Thus, the reported rates are slightly higher. For instance, chlamydia rates in women aged 40–59 were 68.2 per 100 000. This was still dramatically less than in younger age groups .
A cross-sectional health insurance clinic-based study in South Korea, conducted in 2009, enrolled 1804 men and women aged over 60 years. There was a very low prevalence of syphilis (4 cases, 0.2%), chlamydia (14 cases, 0.8%) and gonorrhoea (0 cases) . In China, a cross-sectional study of 11 461 STI clinic patients from eight cities in Guangxi Province included 944 individuals 50 years and older. Syphilis infection was present in 12.7% of this age group . Notably, there is a lack of detailed epidemiological data from the African and Pacific regions on STI diagnosis rates in older populations, other than HIV .
Trichomonas vaginalis is one of the most prevalent STIs worldwide and may be the exception to the rule of younger individuals being most at risk of curable STIs. Until recently, relatively little was known about T. vaginalis risk factors due to its commonly asymptomatic nature and lack of sufficiently sensitive and specific diagnostic tests, particularly for men. Using T. vaginalis nucleic acid amplification tests, a recent US study found it to be the predominant STI in women over the age of 20 years, in contrast with Chlamydia trachomatis, which was more prevalent in younger women . The mean age of women infected with T. vaginalis (30.6 years) was significantly higher than those infected with C. trachomatis (22.3 years) and Neisseria gonorrhoeae (21.6 years). The same US research group also reported a similar age-related prevalence of T. vaginalis among men. The average age (39.9 years) of T. vaginalis-infected men was almost a decade older than in infected women, and, again, infected men were significantly older than those with C. trachomatis or N. gonorrhoeae (27.6 and 25.9 years, respectively) . The reasons for these significant age differences between T. vaginalis and other curable STIs are unclear. In men, it may be partly due to age-specific sexual partnerships with older infected women, among whom long duration of infectiousness  and changes in reproductive hormone levels  have been suggested to contribute to higher T. vaginalis prevalence.
DIAGNOSIS OF HIV IN OLDER AGE
Of all STIs, most published literature is available on HIV diagnoses in older age. In 2005, there were 2.8 million adults aged 50 years and older living with HIV . It is estimated that by 2015, 50% of the US HIV-infected population will be aged over 50 years. The average age of HIV-infected populations in developing countries can also be expected to increase, with roll out of antiretroviral therapy (ART) . This clearly is due to ageing of the already HIV-infected population. However, there is growing evidence that the rate of new HIV diagnoses in people older than 50 years is not insubstantial, both in developed and developing settings [27,28▪,29,30]. For instance, in 2010, people over 50 years accounted for 14% of new HIV diagnoses in the United States . Importantly, HIV diagnosis often occurs later in older people, as seen in 2010 in the United Kingdom, where late diagnosis among older adults (aged 50 years and over) was significantly more common than in younger adults (62 vs. 48%, P < 0.0001) . This is of concern as delayed HIV diagnosis is associated with an increased risk of both AIDS and death , and increasing age is also an independent predictor of AIDS/death among HIV-infected individuals . Frustration has been voiced at the lack of acknowledgement and engagement by world authorities such as the United Nations with the increasing challenge of HIV and ageing . Other professional geriatric and HIV-medicine groups, however, have collaborated to create guidelines for prevention and detection of HIV in older adults [34▪▪], and the Office of AIDS Research of the National Institutes of Health has commissioned a working group to develop an outline of the current state of knowledge and areas of critical need for research in HIV and ageing .
HIV awareness, attitudes, behaviour and testing were assessed in eight countries in sub-Saharan Africa from 2005 to 2007. Among 722 adults aged 50 years and older, HIV knowledge was significantly lower than for younger adults. Older adults were half as likely to be ever tested for HIV. These factors have the potential to greatly impact on HIV transmission among older, sexually active adults [36▪]. HIV risk in older populations was measured in a large longitudinal study in Malawi, with questionnaires and HIV testing undertaken between 2004 and 2008. The authors found that although HIV prevalence declined at older ages, the likelihood of HIV infection remained considerable over age 50 years. This older population contributed 43.5% and 16.3% of the male and female HIV disease burden in this sample. However, HIV incidence was not measured [28▪].
A study of 8846 people aged 16 and older conducted in rural South Africa from 2004 to 2009 examined the impact of age at initiation of ART on mortality. After adjusting for baseline characteristics, the overall mortality risk was 32% higher for those who initiated ART at 50 years or older compared with those initiating at age 25–49 years. Interestingly, this difference was only apparent in the first year of ART [37▪▪]. Mathematical modelling revealed sobering predictions on the impact of the current ART roll-out on age-specific and sex-specific HIV prevalence in South Africa up to 2040. They predicted that while HIV prevalence in the 15–49 years group would more than halve, HIV prevalence in the population aged 50 years and older may nearly double in the same period. Thus, increased prevention efforts need to be concentrated on older people in Africa .
A considerable proportion of MSM continue to be sexually active into their later years and the sexual repertoire of these older MSM may include higher risk sexual behaviours that place them at an elevated risk of STIs . In the United Kingdom in 2010, 13% of newly HIV diagnosed MSM were older than 50 years, whereas less than 5% of newly diagnosed heterosexuals were aged over 50 years. It was reported that as MSM age, they are less likely to be tested for HIV . In the United Kingdom in 2011, large increases in STI diagnoses were seen in MSM, with between 15 and 20% of STI diagnoses occurring in men aged 45 years and older. The ongoing epidemic of lymphogranuloma venereum (LGV) in the United Kingdom , Canada  and the Czech Republic , among other countries, is primarily in older, HIV-positive MSM over 40 years, which contrasts with the much younger peak age affected by other bacterial STIs .
SEXUAL BEHAVIOURS IN OLDER POPULATIONS
Certain circumstances that increase higher risk sexual behaviours and potential STI acquisition in older populations have been proposed in the research literature. These include increased numbers of new partners due to longer life; better health and higher rates of divorce; lack of awareness of sexuality and sexual activity by healthcare professionals with a consequent lack of communication about sexual health and HIV risk; omission from STI prevention and health promotion programs; decreased condom use and lower rates of STI testing; the introduction and extensive uptake of erectile dysfunction medications for sexual functioning, and the increase and ease of foreign travel to countries with easy to access sex industries [20,30,44▪,45▪,46].
A number of recent studies have assessed sexual behaviour among older populations. In a study in sub-Saharan Africa , men aged 50 years or older were more likely to have had two or more sexual partners in the past 12 months than those aged 15–49 in four of seven countries. In Malawi, almost half (n = 192) of women aged 50–64 years and a quarter aged 65 and older (n = 68) reported recent sex. The majority of men aged 50–64 years and aged 65 years and older reported recent sex (84% and 75%, respectively) [28▪]. Very high rates of commercial sex worker contact (46%) among men aged 50 years and older were reported in a cross-sectional study in China, with 24% reporting multiple sexual partners and less than 4% reporting condom use . A subgroup analysis of 120 older women aged 46 years and older attending a UK GUM clinic showed that most (70%) had been recently sexually active and more than half (59%) did not use condoms [12▪]. In the South Korean study of people aged 60 years and older discussed above, though the response rate was poor (14%), of those who completed a sexual behaviour questionnaire, 26% did not use condoms and 10.6% of men reported contact with commercial sex workers in the past year .
Bateson et al.[45▪] postulated that internet dating may place older women at risk of acquiring STIs, as negotiating safe sex with new partners may be unfamiliar and challenging in later life. They surveyed 1788 Australian women using an internet dating service and found that while women aged 40 years or over were more likely to discuss STIs with a new partner, they were less likely to refuse sex without a condom compared with women younger than 40 years. The relationship between oral erectile dysfunction medication (OEM) use and STI acquisition was explored in a US study based on pharmacy and medical claims from 1997 to 2006 for 1 410 806 men aged over 40 years. STI diagnoses before OEM prescription were higher in men who were prescribed OEM in the subsequent year. After OEM prescription, they continued to have higher rates of STIs than nonusers, but they did not experience an increase in STI rates in the year after OEM prescription. This strongly suggests that the association between OEM use and STI acquisition is related to individual characteristics of the person seeking OEM, and is not caused by the use of OEM themselves .
BIOLOGICAL SUSCEPTIBILITY TO SEXUALLY TRANSMITTED INFECTIONS IN OLDER POPULATIONS
It is possible that older individuals have different susceptibility to STIs than their younger counterparts. Physiological changes can affect the sexual responses of men and women and may inhibit or enhance sexual function as people age. In women, lower oestrogen levels from peri-menopause onwards may lead to decreased vaginal secretions during sex . The resultant vaginal dryness and thinning may facilitate transmission of STIs due to microabrasions as a result of sexual intercourse [19,49]. Humoral and cellular immunity, T-cell activity and immunoglobulin production may be impaired in older age and STIs can mimic menopausal symptoms, with chlamydia and gonorrhoea potentially presenting as pelvic pain, deep dyspareunia and postcoital bleeding .
In many settings, there has been a recent increase in STI incidence rates in older age, which parallels increases observed in all age groups. Compared with younger people, STIs remain rare and routine STI screening is not warranted in all older people. In contrast, in both developing and developed settings HIV is becoming increasingly common in older people. Emphasis needs to be placed on education and prevention strategies for all people at greater risk of HIV, regardless of age. Improved longevity, evolving societal norms and physiological changes may place older people at risk of HIV and other STIs. This necessitates the correction of healthcare provider assumptions of sexuality and sexual health in older populations and the development of age appropriate interventions designed to impart knowledge and provide the requisite skills needed to reduce STI risk in older age.
I.M.P. (#1016307) and D.J.T. (#1013353) are supported by Postdoctoral Training Fellowships from the National Health and Medical Research Council. The Kirby Institute is affiliated with the Faculty of Medicine, University of New South Wales and is funded by the Australian Government Department of Health and Ageing. The views expressed in this publication do not necessarily represent the position of the Australian Government.
Conflicts of interest
There are no conflicts of interest.
REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
- ▪ of special interest
- ▪▪ of outstanding interest
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