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> The latest worry is infection by the bacteria Chlamydia trachomatis,
> which has no symptoms.
This is not so. I have been a social worker in an emergency room for many years, and one of my tasks has been to deal with some of the interpersonal consequences of sexually transmitted diseases. In fact, Chlamydia does have symptoms, the problem is that they can take a long time -- up to a year -- to develop. Doctors say it is "indolent." One can walk around with Chlamydia for a long time, entirely symptom-free, and infecting any sexual partner. In girls and women it typically rears up suddenly in the form of Pelvic Inflammatory Disease, a whopping infection of the fallopian tubes, which can do much damage and also is prostratingly painful.
One of the complexities to this, which physicians and patients often ask me to help sort out, is the question: who infected who? Since infecting your partner with a nasty illness is problematic in a relationship, the question is often key. Gonorrhea is easy -- get infected today and you'll be uncomfortable in a few days, but Chlamydia is an interpersonal conundrum.
Both diseases are significant, of course, as evidence in child sex abuse cases, another matter I spend a fair amount of time with. Some of the same issues of latency and symptomatology apply to this as well.
Christopher Rhoades Dÿkema