Management of unprotected sexual encounters

Condom use during vaginal, anal or oral sex provides protection against many sexually transmissible infections (STIs). “Unprotected sex” (sexual intercourse without the use of a condom) may lead a person to seek medical advice and request testing for STIs. The risk of infection for an individual is assessed taking into account the number of partners and exposures, the transmission efficiency of each pathogen, and the estimated prevalence of each STI within a population defined by biological and/or behavioural risk factors. These factors include sex, age, the number and sex of sexual partners, and condom use. Transmission efficiency, which depends on both the likelihood of transmission for each intercourse episode and the duration of infectiousness for each organism,1 is relatively high for gonorrhoea, chlamydia and early syphilis. As the infection status of a sexual partner is often unknown, clinical management of a patient after an unprotected sexual encounter usually involves estimating an individual’s risk according to epidemiological information. Given that diagnosis of an STI may cause considerable distress, and that sexual contacts also need to be tested and treated in the case of a confirmed STI, accuracy of test results is important. No test is completely sensitive and specific: when testing is targeted at people at greatest risk, positive test results are likely to reflect true positive cases, but there is a significant risk of false-positive test results when low-prevalence populations are tested.

Population groups at increased risk of STIs include young people, gay and other homosexually active men, and Indigenous people.

Genital chlamydia is the most common notifiable infection in Australia, with 35 189 cases reported in 2004. From 2000 to 2004, overall population rates of reported diagnoses increased in all Australian states and territories, doubling from 91.4 to 186.1 cases per 100 000 population.2 The highest and most rapidly increasing rates of infection were seen in the 15–19 years and 20–29 years age groups.2

Chlamydial infections in both men and women are commonly asymptomatic, and yet the majority of infections in men are detected in those presenting with urethral symptoms, suggesting that many infections remain undiagnosed.3 Risk factors include, for both sexes, change in sexual partner, higher number of sexual partners and inconsistent condom use, and, for women, being under 25 years of age.4

In women, there is clear evidence that detection and treatment of chlamydial infection reduces sequelae of pelvic inflammatory disease, such as chronic pelvic pain, infertility and ectopic pregnancy.5 Opportunistic chlamydia testing is therefore most important for young women, who experience the highest rates of infection, in order to protect their future reproductive health. In young men, there is little evidence of benefit from chlamydial screening, but this may be related to a lack of research in this area.4 In addition, the strategy of opportunistic testing may be more difficult to apply to young men, who less frequently present to general practitioners for reproductive and sexual health problems than young women. However, a study of remote communities in Northern Canada showed that STI screening of both men and women in high-prevalence populations significantly reduced the incidence and prevalence of chlamydia, whereas screening of women only did not.6

Although teenage pregnancy rates have been falling since the 1970s, Australia still has much higher rates than many western European countries.7 Unplanned pregnancy is particularly associated with adverse health outcomes for young women from socially disadvantaged backgrounds.7,8 Condoms and the oral contraceptive pill are the most commonly used forms of contraception among teenage Australian women. However, for reasons that are unclear, contraceptive use among sexually active women in this age group remains inadequate.9

Very high rates of STIs — including gonorrhoea, genital chlamydia and syphilis — among Indigenous Australians are reflected in the high notification rates for these diseases in Australian states with large Indigenous populations.2 Health outcomes are poor, with Indigenous women experiencing endemic rates of pelvic inflammatory disease and infertility.11 Although rates of HIV among Indigenous people remain comparable to those of the general population, the much larger proportion of cases attributed to heterosexual transmission2 prompts ongoing concern about the potential escalation of HIV infection among Indigenous people. More interventions are urgently needed, including community testing and treatment programs, which have demonstrated the ability to lower the prevalence of chlamydial and gonococcal infection.12

After a long period of decline, new diagnoses of HIV infection increased between 2000 and 2004, with 86% of newly acquired infections occurring among men who reported homosexual contact. The highest population rates of HIV diagnosis were recorded in New South Wales (5.9 per 100 000 population) and Victoria (4.3 per 100 000 population). Highest rates of diagnosis of newly acquired HIV infection also occurred in these states (1.7 and 1.3 per 100 000 population, respectively), and Queensland and South Australia recorded their highest rates over the past 10 years in 2004 (1.2 and 1.1 per 100 000 population, respectively).2

In the light of evidence of increased HIV transmission associated with concurrent STI infections,13 the recent re-emergence of syphilis2 and increased rates of other bacterial STIs2,14 among gay men is of concern. Health in Men, a community-based cohort study of HIV-negative homosexual men in inner Sydney, is expected to provide information that will help determine the recommended frequency of testing for gay men. Findings to date strongly support the need for regular STI screening.14 Current testing recommendations15 are detailed in Box 3. Among gay Australian men, there is evidence that sexual risk decisions are significantly influenced by knowledge of HIV status,16 and that men who are attached to gay communities are more likely to have had a recent HIV test.17 Homosexually active men outside gay communities and in regional areas may be less able to exercise informed sexual choices.

Evidence to support the efficacy of antiretroviral postexposure prophylaxis (PEP) after sexual exposure to HIV is indirect. (This evidence includes studies of mother-to-child HIV transmission, observational studies of PEP after potential sexual exposure to HIV, and a case–control study of health care workers in which zidovudine treatment after percutaneous exposure to HIV reduced HIV seroconversion by 80%.)18 Nevertheless, PEP has been found to be cost-effective when used after sexual exposures that carry a significant risk of HIV transmission.19 A combination of two or more antiretroviral drugs commenced within 72 hours of exposure and continued for 28 days is likely to significantly reduce the risk of contracting HIV.18 Australian guidelines20 advocate the use of PEP after a sexual exposure that carries a substantial risk of transmission and involves a person known or likely to be infected with HIV (Box 4). Fears that availability of PEP for use after sexual exposures would lead to increased sexual risk behaviour have so far proved groundless.18

Presentation for PEP also provides an opportunity for STI testing: among men seen for PEP at a Sydney hospital between 2001 and 2004, rectal chlamydial and gonococcal infections were detected in 4.3% and 2.4%, respectively.21 Although there is still uncertainty about the efficacy of antiretroviral PEP, the effectiveness of prophylaxis for hepatitis B virus (HBV) is well established.

STIs also affect the general population, and a wide variety of asymptomatic people may present to GPs requesting STI/HIV testing after unprotected intercourse23 or condom failure. In this situation, clinicians should select tests for STIs that are significant or reasonably frequent in the population and are amenable to management.

Tests may include serology for HIV, HBV and syphilis, as well as PCR testing for chlamydia on a first-void urine sample. Herpes simplex virus serology should be avoided, as it may be impossible to determine the clinical significance of a positive result in an asymptomatic person, leading to psychological distress without benefit.24 PCR testing for gonorrhoea has a high false-positive rate outside high-prevalence populations, and a confirmatory test should be used in positive cases.25 Gonococcal PCR testing can be confined to people with a clinical syndrome such as urethritis, cervicitis or pelvic pain; groups in which the prevalence of gonorrhoea is higher than average (including Indigenous people and gay men); and victims of sexual assault. After a specific risk exposure such as sexual assault, baseline and follow-up testing are indicated, taking into account varying incubation periods for each infection.26

Choice of investigations after unprotected sex is guided by sexual history, with opportunistic STI testing indicated for population groups at increased risk. Condom use remains the most effective HIV prevention strategy,28,29 but targeted use of PEP is considered to be a cost-effective biological adjunct to HIV prevention when its use is restricted to high-risk exposures. In Australia, HIV-infected people and their partners, as well as homosexually active men, should be informed about PEP. GPs are well placed to recognise patients at increased risk of STIs, perform appropriate STI testing and refer patients for postexposure HIV prophylaxis if appropriate.