One in ten sexually active young British adults carries chlamydia, which can cause serious damage to fertility. And as infection rates rise steeply, doctors have stepped up warnings on the dangers of this disease. The awareness campaign has focused on women, as chlamydia was thought to affect them particularly. But new research now shows that the risk to men is equally worrying: men with chlamydia have three times the normal number of sperm with genetic damage. The findings coincide with recent indications that infection rates are rising fast for a range of other sexually transmitted infections (STIs) and that young people, who are most at risk, have become complacent about public health warnings.

Convincing young people to be responsible in their sexual behaviour is hard enough; it is particularly difficult to make men aware of the dangers to themselves of chlamydia, as there are often no symptoms and many are unaware that they are carrying the bacteria. Nevertheless, Britain’s national screening programme has found that 10.2 per cent of those aged 18-25 are infected, and even among older groups less at risk the rate is running at 5 per cent. Male reluctance to be tested is particularly unfortunate, as chlamydia is easily treated with antibiotics. Typically, a week’s course of doxycycline or a single dose of azithro-mycin is sufficient. If untreated, however, the disease can produce real harm: sperm suffers a form of genetic damage called DNA fragmentation, which can cause it to die as well as hindering its ability to fertilise eggs and normal embryonic development. Tests in America have found that more than one in three infected men have damaged sperm, although this recovers after treatment. For women, the consequences are more obvious: chronic infection will cause damage to the Fallopian tubes that is not normally reversible.

Any infection, however, also increases the risk of catching other STIs, some of which are far more serious. Syphilis and gonorrhoea, diseases that cause panic a few centuries ago, are on the rise again after falling sharply in the 1980s, when the warnings on Aids produced generally more responsible sexual behaviour. Between 1997 and 2006, syphilis increased by 1,607 per cent, gonorrhoea by 46 per cent, chlamydia by 166 per cent and herpes by 36 per cent. The number of cases of gonorrhoea, at 19,000 a year, is still below the peak rate of 80,000 in 1975. But the rise is similar to the other worrying trend, which appears to be born of complacency: the rise in HIV infection.

The Conservative Government’s dramatic public awareness campaign to promote safe sex amid fears of an Aids epidemic in the 1980s was one of the most successful of all public health campaigns. HIV-deniers ridiculed the stark warnings, saying that the relatively small incidence of Aids showed there was never a danger; more responsible commentators applauded a campaign that may have prevented the kind of social catastrophe now seen in southern Africa and elsewhere. The message needs repeating. It need not be so apocalyptic: Aids can now be contained, if not cured. But it is still important to warn people about the dangers, physical, social and moral, of irresponsible sexual behaviour. The message needs constant updating, both for the naive young and for complacent adults, and no taboo should curb communication. The choice is clear: spread the message or allow infection to spread.