Many times, a person treated for chlamydia will see symptoms clear up, only to reemerge later. A review published in Infection and Immunity has found the culprit: your gut.

"Chlamydia trachomatis not only infects the reproductive tract, but abides persistently-though benignly-in the gastrointestinal tract. There it remains even after eradication from the genitals by the antibiotic, azithromycin, said first author Roger Rank, of the Arkansas Children's Research Institute. "And that reservoir is likely a source of the all-too-common reinfections that follow treatment," according to the press release announcing the review.

In the past, reemergence of symptoms was blamed on continued intercourse with infected partners, a believable theory considering the infection is usually asymptomatic in men.

Chlamydiae have long been assumed often to persist within the genital tract in a non-replicating form, but Rank said there is no evidence for this.

"While all agree that chlamydiae may persist in a patient for long periods of time, and that recurrent infections do develop, there has been no agreement on how and where and in what form chlamydiae persist," he said.

In a recent study, coauthor and Arkansas colleague Laxmi Yeruva showed in mice that azithormycin eradicated the genital infection, but not the gastrointestinal (GI) infection.

Rank showed further-also in mice-that chlamydial infection of the GI does not elicit an inflammatory response, and never resolves, unlike in the genital tract.

"However, we found that GI infection does produce a strong immune response that can actually be effective against a genital infection, but that is unable to cure the GI infection," said Rank.

Chlamydia trachomatis is the most common cause of sexually transmitted disease in the world. In the US, approximately 1.4 million cases occur annually, according to the US Centers for Disease Control and Prevention. Adolescents are most affected, and 6.8 percent of sexually active females ages 14-19 become infected annually.