Contribution of PCR to Differential Diagnosis between Patients with Whipple Disease and Tropheryma whipplei Carriers.

Differentiation between Whipple disease (WD) patients and patients carrying Tropheryma whipplei but suffering from disease other than WD ("carriers") remains complex. We aimed to evaluate T. whipplei PCR among patients with WD and carriers in a large cohort at our referral clinical microbiology laboratory. This is an observational retrospective cohort study, including all patients between 2008 and 2020 with at least one positive result for T. whipplei using the real-time PCR RealCycler TRWH-UX kit. A total of 233 patients were included: 197 were considered carriers, and 36 had WD. Among the WD patients, 32 underwent biopsies, of which 18 (56%) had a positive periodic acid-Schiff (PAS) staining. Among the 27 duodenal biopsy specimens, 13 (48%) were PAS positive. PCR results before antibiotic treatment were positive in both feces and saliva in 16/21 WD (76%) patients and 68/197 (35%) carriers ( < 0.001). Duodenal biopsy specimens yielded positive PCR in 20/22 (91%) WD patients and 27/72 (38%) carriers ( < 0.001). The cycle threshold () value detected in duodenal biopsy specimens from WD patients was significantly lower than that of carriers ( < 0.001), regardless of the PAS staining results. For a diagnosis of WD, duodenal PCR sensitivity and specificity at a value below 30 were 52.4% and >99.9%, respectively. The high specificity of duodenal PCR with low values may help confirming the diagnosis of WD, especially in patients with negative PAS results in digestive biopsy specimens, who represent half of all patients. A low PCR value from a duodenal biopsy specimen provides valuable guidance, especially in patients with PAS-negative results.