Giardia diagnostic methods in human fecal samples: a comparative study.

Several methods were tried for Giardia detection in stool. This study aimed to compare between the results of ordinary microscopy, direct immunofluorescence assay (DIF), and flow cytometry (FC) for the detection of Giardia cyst in human stool samples. The study included 84 children recruited from outpatient clinics of Mansoura University Children Hospital. Fecal samples were processed and examined for Giardia cysts using conventional microscopy, DIF, and FC. Among 84 fecal samples, 40 (47.6%) were diagnosed as Giardia-positive by saline wet mount, while DIF and FC detected 52 (61.9%), and 38 (45%) Giardia-positive cases, respectively. When compared with DIF as a gold standard method, ordinary microscopy had 76.9% sensitivity and 100% specificity while the FC had a sensitivity of 73.1% and 100% specificity, with statistically significant differences between DIF and the other two methods (P < 0.05). DIF was able to detect as few as 500 cysts/g of concentrated stool, yielding a threshold higher than ordinary microscopy (1,800 cyst/g) even after concentration. It is concluded that direct microscopic examination is reliable in Giardia diagnosis as a first choice test. DIF is an excellent technique in clinically suspected cases after negative microscopy. FC was found to be less sensitive to obtain accurate organisms' count but it could be an effective alternative method for the detection of Giardia cysts, especially for large-scale epidemiological studies or extensive surveillance programs as it has the beneficial attribute of speed and do not depend on an experienced microscope viewer. However, DIF remains the gold standard while FC still requires significant technical improvements before it can compete with DIF for Giardia diagnosis.

Degree of symptoms versus copro-antigen levels in Giardia lamblia infection.

A total of 82 out-patients were examined for Giardia copro-antigens and 12 neonate stool samples as control. ELISA had a sensitivity of 100% and specificity of 91.67%. ELISA (O.D.) had neither significant correlation to Giardia cyst count, to stool consistency or presence of blood, mucus or fat in stool, nor to age but positive correlation to the severity of diarrhoea, colic, nausea, anorexia, weight loss, distension and fatigue. Giardia cyst count was higher in cases with loose stool, while ELISA (O.D.) correlated positively with symptoms except constipation and vomiting. The different in clinical outcome of giardiasis can be attributed, partially to strain differences and host resistance.