Abstract
<jats:p>Background Diarrhoeagenic Escherichia coli pathotypes (DEP) are leading causes of diarrhoeal illness worldwide, yet their identification requires molecular methods often unavailable in resource-limited settings. We evaluated E. coli load as a potential screening indicator for DEP presence in diarrhoeal samples. Methods Stool samples from 252 diarrhoeal patients and 70 non-diarrhoeal controls were analyzed. E. coli load was quantified by serial dilution plating on MacConkey agar. DEP (ETEC, EPEC, EAEC, EIEC, EHEC) were identified by multiplex PCR targeting virulence genes. Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis with calculation of sensitivity, specificity, predictive values, and likelihood ratios at multiple cutoff thresholds. Results DEP were detected in 56% (142/252) of diarrhoeal and 26% (18/70) of non-diarrhoeal samples (p < 0.0001). DEP-positive diarrhoeal samples exhibited significantly higher E. coli loads than DEP-negative samples (geometric mean: 1.0×108 vs. 5.7×106 CFU/g; p < 0.0001; Cohen’s d = 1.2). ROC analysis yielded an area under the curve (AUC) of 0.78 (95% CI: 0.73–0.85; 5-fold cross-validated AUC = 0.79, SD 0.05). At the optimal cutoff (≥1.4×107 CFU/g), sensitivity was 83% (95% CI 76–88%), specificity 66% (56–74%), positive predictive value 76% (68–82%), and negative predictive value 75% (66–83%). A strong positive correlation was observed between E. coli load category and DEP detection rate (Spearman ρ = 0.49, p < 0.001). Conclusions E. coli load demonstrates moderate discriminatory power suitable for triage but not for diagnosis (AUC = 0.78); the substantial distributional overlap between DEP-positive and DEP-negative samples precludes use as a standalone test, but E. coli load quantification offers a simple, inexpensive method for prioritizing samples for confirmatory molecular testing in resource-limited settings.</jats:p>