At the beginning of the clinical investigation, the principal diagnostic hypothesis was of ulcerative colitis. The clinical symptoms, the presence of a polyp were compatible to this hypothesis, and the markers of intestinal inflammation were positive, notably the fecal calprotectin. However, the histopathological exam at the sixth month of evolution did not show elements commonly seen in ulcerative colitis, such as neutrophilic infiltrate in mucous and submucous layers; mucosal edema, focal hemorrhage, depletion of mucus [1,3]. Instead, the exam showed a chronic inflammatory process pointing out to a secondary cause of proctitis. Immuno-histochemistry screened for three common virus, but at the end the final diagnosis was serological. In this way, the presence of IgM after so much time of clinical evolution was the principal marker of active infection. If this patient showed only IgG, perhaps the diagnosis would have not been so clear.

Compared to 1833, when the first clinical description of the veneral lymphogranuloma was done [6], the taxonomical classification of the bacteria of the family Chlamydiaceae has changed a lot, especially in the last ten to fifteen years, with protein and molecular markers [7-9]. Currently, it is considered that this family comprises a single genus – Chlamydia – with 16 obligatory intracellular parasite species. Two species, C. trachomatis and C. pneumoniae, infect humans, causing conjunctivitis (and subsequent blindness), pneumonia (and subsequent death) and anogenital inflammation (and subsequent infertility). Chlamydia trachomatis is subdivided into three biovars, according to the disease provoked (conjunctivitis, veneral lymphogranuloma or inespecific anogenital inflammation) [7-9]. The biovars are subdivided into serovars according the occurrence of certain major outer membrane protein complexes, totalling 13 genotypes. The serovars L1 to L3 cause veneral lymphogranuloma; the sorovars A to C cause conjunctivitis and the serovars D to K cause anogenital inflammation, which is frequently asymptomatic or with mild symptoms [7-9].

Being an intracellular parasite, the diagnosis via culture is complex, as not all laboratories of clinical analysis are equipped to do so [1,6]. However, with the appearance of diagnostic resources based on antigenic and molecular markers, several epidemiological screenings have been carried out, showing a prevalence of 5 to 20% according to the population sampled [10-14]. That is, among the sexually transmitted infections, Chlamydia trachomatis shows sharp geographical differences, but occurs with a considerable frequency hence it should be screened more routinely in the daily clinical practice.

Regarding manifestations of anogenital infection by Chlamydia trachomatis, there is a dissociation between genital and anorectal manifestations, that is, there are women who present with only cervicitis/endometritis/salpingitis, with only proctitis or both, as well as there are men who only present urethritis/prostatitis; only proctitis or both[13,14]. In the epidemiological screenings where the sexual practices were lifted up, the practice of anal sex could not be related with the infectious focus, that is, a significant portion of the patients deny this but shows with proctitis as well a significant portion report this but present with only genital infection [13,14].

The treatment of Chlamydia trachomatis infection is done with macrolides or tetracyclines, and quinolones have shown some efficacy [4,5]. The beta-lactams reduce infectivity and speed of replication of C. trachomatis, but they are not very effective in its eradication, and when the patient stops taking them, there can be a growth of a strain resistant to macrolides⁵. There is the description that a single dose of 1g of azithromycin can eradicate Chlamydia infections, but the therapeutic failure rate, of about 20%, points out that this strategy can induce antimicrobial resistance in a relatively short time [4,5]. To mild anorectal infections, Hocking et al.[5] recommend at least 7 days of antibiotics, while to more extensive forms of veneral lymphogranuloma, the use of antibiotics needs to be extended to 3 weeks or more.

As a conclusion, the case herein reported points out that in the differential diagnosis of inflammatory bowel disease, the search for Chlamydia infections should be reinforced, as it has been commonly done to HIV and syphilis.