STIs from oral and anal sex: why throat and rectal swabs matter

There is a simple, common, and consequential gap in a lot of STI testing: a urine sample only checks the genital site. If sex has involved the mouth or the anus, an infection can be sitting quietly in the throat or the rectum, and urine testing will sail straight past it and hand back a clean result. That result is not wrong so much as beside the point.

Why the site is not a technicality

Chlamydia and gonorrhoea live happily in the throat and rectum, and infections there are almost always silent, so nothing prompts anyone to check. This matters for more than the individual. The throat, in particular, is now thought to be where resistant gonorrhoea is bred: the bacterium sits alongside its harmless relatives and swaps resistance genes with them, then gets passed on. A missed throat infection is not just your problem; it is a small contribution to the wider resistance problem that could one day leave gonorrhoea untreatable, which would make everyone's infection the hard-to-treat kind.

The rectum is not a gentle site either. Rectal chlamydia includes a more aggressive form, LGV, which is not the quiet infection its cousin usually is: it can cause painful proctitis, with rectal pain, bleeding, discharge and a constant urge to go, and left untreated it can scar the bowel and form abscesses and fistulas that need weeks of antibiotics and sometimes surgery to put right. Silent does not mean harmless; it means undetected, and undetected is exactly how the serious ones get their head start.

What it means in practice

Where oral or anal sex is relevant, a throat swab and a rectal swab are added for chlamydia and gonorrhoea. They are quick, and in many cases self-taken, which most people find far less awkward than they feared. This applies to anyone whose sex has involved oral or anal contact, of any gender or orientation. A doctor asks a few practical questions purely to work out which sites to test; the questions are the same for everyone and exist only to get you an accurate answer.

The honest summary

A urine test cannot find what it never sampled. If you have had oral or anal sex, throat and rectal swabs are what make the screen honest, and skipping them can leave a silent infection to do harm and, in the case of gonorrhoea, to help breed the resistance that threatens everyone. A short, matter-of-fact conversation is all it takes to get it right.