Just to say, it was only chlamydia and has cleared away. I'm just curious as to how I got it in the first place.

Quick background, I've been a part of a small group of guys who fuck each other without condoms for ten years; there's four of us altogether. Three are in the medical profession and undergo constant health screenings; I'm the cautious one when it comes to having any kind of sex outside of the group. Cautious enough for some random hookups to think I'm not worth the time to meet with.

When I had my annual check-up last month, I asked for the standard STD tests. It returned saying I had rectal chlamydia. Nothing too odd there since I mainly bottom.

What was odd was that none of my three friends ended up having chlamydia; meaning none of them had it to begin with. So I'm wondering exactly how I got it in the first place. I only had sex with someone outside of our group once between my 2022 and 2023 check-ups, and the random person only ground his bare dick against my hole. No penetration of any kind, just some innocent humping.

This was a day before my annual check-up, hence no penetrative sex. And nobody in the group had an STD or STD scare in the last year. We're good at keeping each other up-to-date on our sexual health.

So one of two things could've happened here. Either I got rectal chlamydia from the one random guy who just ground his dick against my hole; or the medical diagnosis was somehow faulty. Both are valid reasons, but I put more stock in the test being faulty since the chances of getting chlamydia from just a dick rubbing against my ass a day before the test is super slim. Especially since a chlamydia test requires a swab to be inserted an inch into your butt where the bacteria lives.

What do you guys think was more likely? Just being honestly curious here about the STD reading. At worst, I got an intense internal bacterial cleanse from the antibiotics I was prescribed.