Hormonal markers of susceptibility to sexually transmitted infections: are we taking them seriously?

When the body is invaded by pathogens, each individual reacts with a battery of non-specific and specific immune defence mechanisms. Sex hormones play an important part in the host's resistance to sexually transmitted infections. This is shown by sex differences,[1] variations in detection of infection according to phase of the menstrual cycle,[2] increased susceptibility during pregnancy,[3] and evidence that use of hormonal contraception predisposes to infection.[4 5] The mechanisms by which specific sex hormones modulate the immune system have been reviewed.[6] This is a complex subject, and it is unfortunate that, in spite of its potential importance, no clear message about sex hormones has emerged or been harnessed to the development of strategies for controlling infection. This paper revisits some of the evidence that hormonal status influences susceptibility to sexually transmitted infections, especially in adolescents, and considers the practical implications of this evidence.

Sex differences

The best example of sex differences in rates of infection and disease for various sexually transmitted viral infections is genital herpes. Many studies report a higher seroprevalence of genital herpes in women than in men in both developed and developing countries,[7 8] after exposure has been controlled for,[9] and in every age group.[8] Among women who were initially seronegative, a higher risk of symptomatic infection and a faster rate of acquisition of herpes simplex 2 virus compared with men was shown in a well designed cohort study.[10] Sex differences were also striking in recent vaccine trials, with the vaccine showing limited protective efficacy against genital herpes for women but not for men.[11]

These sex difference were not attributed to sex hormones but to anatomical differences that are thought to make it easier for the virus…