The bacteria that cause chlamydia might be trickier than we knew. In a new study this week, scientists have found evidence that these bacteria can hide in our intestines. The findings might explain why some people experience re-occurrences of chlamydia even after successful antibiotic treatment, the researchers say.

Chlamydia in humans is caused by Chlamydia trachomatis (other animals, including koalas, have their own version ). It’s the most commonly reported sexually transmitted infection in the U.S.

, with more than 1.6 million documented cases in 2022. Though most infected people will not become sick, some will experience gruesome symptoms like bloody urination, genital discharge, or rectal pain and bleeding, depending on where the infection is located.

Untreated cases of chlamydia can lead to life-changing complications like pelvic inflammatory disease, arthritis, and even infertility, while also raising the risk of catching other STIs. Researchers at the University of Würzburg in Bavaria, Germany, led this new research, who were hoping to get to the bottom of a persistent mystery about chlamydia. Though infections remain very treatable with antibiotics (for now, at least), some people will later return to their doctors with another bout of chlamydia.

When scientists have looked at these cases, they’ve sometimes found that people were reinfected by strains genetically identical or very similar to the bacteria that first infected them. It’s possible that some of th.