Prevalence of intestinal spirochaetosis in serrated polyposis syndrome compared with other colorectal polyp conditions: a case-control study in Japan.

OBJECTIVE: Serrated polyposis syndrome (SPS) is the most common form of colorectal polyposis syndrome. Most SPS cases are sporadic, and the environmental factors underlying its pathogenesis remain poorly defined. Intestinal spirochaetosis (IS), an infection of the colonic epithelium by Brachyspira species, is frequently asymptomatic and its clinical relevance is uncertain. Here, we examined the potential association between IS and SPS. METHODS: In this retrospective case-control study at two centres in Japan, IS prevalence was assessed in 64 patients with SPS and 382 non-SPS controls who underwent colonoscopic polypectomy. Controls were classified as having only conventional adenomas (Ctrl-CA) or serrated polyps not meeting the diagnostic criteria of SPS (Ctrl-SP). RESULTS: Histologically confirmed IS was detected in 12/64 (18.8%) SPS cases and 6/382 (1.6%) controls (OR 14.5, 95% CI 5.2 to 40.2; p<0.001). IS prevalence increased stepwise across Ctrl-CA, Ctrl-SP and SPS groups (1/274 (0.4%), 5/108 (4.6%) and 12/64 (18.8%), respectively; OR 6.5, 95% CI 3.1 to 13.8; p for trend <0.001). Among the 12 IS-positive SPS cases, all had a history of cigarette smoking and altered bowel habits were common. Furthermore, IS detection rates did not differ based on anatomical locations of polyps, but considerable intraindividual variability was observed across serial colonoscopies, suggesting possible episodes of clearance and reinfection. Real-time PCR and sequencing analyses demonstrated that all IS-positive cases were attributable to Brachyspira aalborgi, a species commonly found in developed countries. CONCLUSIONS: This study reveals a novel association between IS and SPS with distinct clinical characteristics in Japan. Considering the retrospective design and small sample size from a single geographic region, further investigation is required to clarify the significance and generalisability of this association.