Of the 53 children enrolled (aged 1.5-7 years), 48 children each provided at least 1 stool sample; 15 children provided at least one stool sample at both time-points and 23 children provided all 4 stool samples. All samples were analyzed by ELISA but only a subset of fresh samples (n=75) were analyzed by a single researcher through microscope due to time limitations. The corresponding 75 samples were assessed by dipstick. Based on ELISA results, 43.8% of the subjects tested positive for giardial coproantigen at Week 0. A similar prevalence (44.7%) was found at Week 4. The percentage of individuals with new infection, self-clearance, chronic infection or with no G. intestinalis infection is illustrated in both for the cohort of children who each gave at least 1 stool sample at each end of the study (n=15) and for the 4-stool cohort (n=23), providing all 4 requisite stool samples. The 4-stool cohort appeared to exhibit a higher percentage of persisting infection compared to the subjects who provided 2 or 3 stool samples.
Percentage of sample subjects displaying new infection, self-clearance, persistent infection, and no infection with G. intestinalis over a 5-week period
Diagnostic agreement among the 75 samples evaluated by all three detection methods was 74.7%. Using ELISA as the gold standard, the microscopic analysis had a slightly higher specificity and positive predictive value (PPV), indicating greater confidence in positive test results relative to the dipstick method (). The dipstick method had a higher sensitivity and negative predictive value (NPV), indicating greater confidence in negative test results relative to microscopic analysis.
Sensitivity, specificity, PPV*, and NPV† of microscope and dipstick test for Giardia detection in stool samples, using ELISA as gold standard
Comparison of intensity of Giardia infection, using the microscopic cyst counts (positive samples only, n=15) vs ELISA absorbance values indicates that all of the positive samples detected by microscopy had high ELISA absorbance values (>1.7), the majority (n=14) having near-maximal absorbance values of >2.9). Alternatively, not all of the samples with high ELISA absorbance values (>1.7) were positive for G. intestinalis with microscopic examination. The range in cyst concentration detected by microscope was 2.000-358.750 × 10 000 cysts/g of faeces. The Spearman correlation, using scaling values as proxies for intensity of infection between cyst count and absorbance reading, was non-significant (p=0.26). The detection limit of the dipstick was 2.000 × 10 000 cysts/g and an ELISA OD value of 2.5.
Subjects with a higher ELISA coproantigen intensity, though not significant, tended to have lower WAZ (r=-0.32, 1-tailed p=0.08). The 1-tailed test was performed after the general consistency of a negative coefficient correlation, i.e. an inverse association between intensity of infection and growth was shown across the board for all three indicators (WAZ, WHZ, and HAZ). No significant correlations were found between ELISA coproantigen intensity and HAZ (p=0.12), or WHZ (p=0.36).