Diagnosis of Intestinal Entamoeba histolytica Infection by Rectal Swab: An International Multisite Cross-Sectional...

Stool samples are the standard specimen for molecular diagnosis of intestinal Entamoeba histolytica infection. Rectal swabs, an easier sample collection method, are increasingly used for diagnosing many enteric pathogens; however, their diagnostic utility for E. histolytica remains insufficiently evaluated.

Stool and rectal swab specimens were collected simultaneously from participants tested for intestinal E. histolytica infection. The detection capability of rectal swabs using a modified DNA extraction protocol was compared with that of stool specimens using E. histolytica-specific quantitative PCR (qPCR).

From four cohorts, 355 sample pairs were collected. In a paired 2 × 2 comparison, 335 pairs (94.4%) yielded concordant results, indicating moderate agreement between stool and rectal swab qPCR (Cohen's κ = 0.636). Overall, 40 cases tested positive by stool and/or rectal swab qPCR, of which 20 were concordant positives. Discordant positive results were observed in the remaining 20 cases and were more common among specimens with relatively high cycle threshold (Ct) values. These discordant cases included 11 stool-positive/rectal swab-negative and nine stool-negative/rectal swab-positive pairs. Sensitivities based on the composite reference standard did not differ significantly between stool (77.5%) and rectal swab (72.5%). Among concordant cases, median Ct values were similar between stool (28.83) and rectal swab (29.56).

Rectal swab qPCR demonstrated comparable detection capability for E. histolytica to that using stool-based qPCR. False negative results also occurred frequently when a single molecular test was used. Further studies are warranted to validate these findings and assess their application in diagnosis and targeted screening, particularly among populations at increased risk for intestinal E. histolytica infection.