A research article (page 179)1 and a letter to the editor (page 218)2 in this issue of the Journal should leave you in no doubt that syphilis is back. After falling precipitously with the onset of the HIV epidemic in the early 1980s, syphilis infection rates are rising dramatically in Australia and the developed world among men who have sex with men.3 Why has this occurred, and what can be done about it?

The prevalence of a sexually transmitted infection (STI) is determined by three factors: the probability of transmission per partnership, the rate of partner change, and the duration of infectiousness. The particular importance of the duration of infectiousness is illustrated by the dramatic 100-fold fall in the prevalence of syphilis following the introduction of antibiotics.4 Another example is in situations where access to health care is poor and duration of infectiousness is therefore prolonged, as in isolated Indigenous communities in Australia. In such communities, both syphilis and gonorrhoea are common, despite rates of partner change being similar to those in the rest of Australia.5 In contrast, gonorrhoea or syphilis struggle to exist in communities with adequate access to health care, unless the rate of partner change is high.

What then has changed among men who have sex with men to cause this sudden rise in syphilis infections in New South Wales and Victoria?

Sexual behaviour has changed, with rates of any unprotected anal intercourse among men who have sex with men having increased by 50% in Australia over the last 10 years — this was also a strong risk factor for incident syphilis in the Health in Men (HIM) study6 mentioned in the research article by Jin et al.1 Oral sex is also transmitting syphilis, despite being considered relatively safe in terms of HIV transmission. Over half of the men in Jin et al’s cases series believed they had contracted syphilis through oral sex,1 and oral sex has been reported as the sole risk factor in up to 50% of cases reported overseas.3

HIV-positive men who have sex with men appear to be at increased risk of syphilis in Australia, representing between 40% and 54% of the cases reported by Jin et al1 and Guy et al.2 In addition, unprotected anal intercourse with an HIV-positive man was a strong risk factor for incident syphilis among HIV-negative men in the HIM Study.1 These findings are consistent with overseas reports that syphilis is more commonly diagnosed in HIV-positive men.3

The critical issue is what can be done now to control this epidemic. Clearly, increasing the use of condoms is important, particularly for anal sex. It is unlikely, however, that condoms will be widely used for oral sex, even though this practice is transmitting syphilis. In addition, reducing the rate of partner change is important, but it has been difficult to demonstrate large effect sizes in controlled studies.7

Substantially reducing the duration of infectiousness may be possible through educational campaigns, increased screening and enhanced contact tracing. Intensive educational campaigns for clinicians and men who have sex with men are fundamental for promoting early diagnosis and treatment, and screening high-risk individuals. Remember, most doctors under the age of 45 have not seen a case of syphilis, and young men are also less likely to be aware of the symptoms and clinical presentation of the infection. Educational campaigns that use the Internet can be relatively cheap and effective. For example, one banner advertisement on gay websites resulted in 32 270 click-throughs to public health websites with syphilis information.8 The cost per “click” varied from $0.05 to $10.8

Increased screening is the only way to detect asymptomatic infection; up to 33% of infections reported by Jin et al in the syphilis case series and the HIM study were asymptomatic.1 Guidelines suggest yearly testing for syphilis for any man who has had sex with another man in the past 12 months.9 This is easily justifiable given the syphilis incidence rate of 0.78 per 100 person years among men in the HIM study, but not necessarily easy to implement because it involves reaching all men who have sex with men, not just those attached to the gay community.1 Screening at every clinic visit for syphilis among HIV-positive homosexually active men may be necessary in view of the higher incidence of syphilis in this group.

STI control is most cost effective if programs are focused on core group members who have large numbers of sexual partners. In the syphilis case series, up to two-thirds of the men had attended sex-on-premises venues or saunas where rates of STI infections have been previously reported to be extremely high.1,10

Contact tracing is an essential part of effective STI control but is difficult among men who have sex with men, whose partners are often anonymous. Nevertheless, innovative programs can prove effective. One study found that contact tracing was relatively effective even though the only identifying information available to public health officials were the “screen names” used in internet chat rooms. In this study, 41 of the 97 contacts of men infected with syphilis were traced through their “screen names”.8

Lastly, information about the epidemic, including the typical clinical features, who is affected, and risk factors for infection, is critical to inform intervention, as indeed both Jin et al1 and Guy et al2 have shown. For example, Jin et al provided much needed information about the usual clinical presentation of syphilis, finding that rash was the most common symptom (42%), but an ulcer or sore was also common (40%).1 As the rash of secondary syphilis is extremely infectious, identifying such cases early will significantly improve control.

Australia’s response will determine if the current syphilis epidemic is remembered as an isolated epidemic or the return of endemic infection. Endemic syphilis will be expensive; both in human and financial costs, not least because it promotes HIV transmission. We need to learn from Australia’s effective and early response to the HIV epidemic that was characterised by community partnership, bipartisan government support, a commitment to harm minimisation and dynamic, original strategies.