Assessment of the sensitivity, specificity, and reproducibility of the indirect immunofluorescent technique for the diagnosis of amebiasis

Comparison of the performance of two spontaneous sedimentation techniques for the diagnosis of human intestinal parasites in the absence of a gold standard

Performance evaluation of diagnostic tests is critical in the search for accurate diagnoses. A gold standard test is usually absent in parasitology, thus rendering satisfactory assessment of diagnostic accuracy difficult. Moreover, reliability (assessed by the study of repeatability) is a rarely studied characteristic of diagnostic tests. This study compared and evaluated the performance (repeatability, concordance and accuracy) of the spontaneous sedimentation technique (SST) and the Paratest for the diagnosis of Giardia lamblia, Entamoeba histolytica complex, Blastocystis spp., Ascaris lumbricoides, hookworm, Trichuris trichiura and Calodium hepaticum. Fecal samples of 143 individuals were separated into three replicates for each test. Concordance and homogeneity of the results between replicates of each test and between tests were evaluated. Proportions of positives, sensitivity and specificity were estimated using a Bayesian Latent Class Model. High repeatability of both tests was found for the detection of intestinal parasites, except for Blastocystis spp. and hookworm. Concordance between tests was generally high (concordance correlation coefficient, 0.72-0.88), except for Blastocystis spp., hookworm and T. trichiura. The Paratest detected more cases of Blastocystis spp. and fewer of hookworm than the SST. The tests were quite discordant in the detection of T. trichiura. A low sensitivity (39.4-49.2% for SST, 35.8-53.8% for Paratest) and a high specificity (93.2-97.2%) were found for both tests. The Paratest presented a slightly higher sensitivity for the diagnosis of Blastocystis spp. (53.8%), and SST did so for hookworm (49.2%). This is the first study on repeatability and accuracy (using a Bayesian approach) of two spontaneous sedimentation techniques. These results suggest underdiagnosis of little dense parasitic forms due to technical limitations in both tests. We conclude that the combined study of repeatability, concordance and accuracy is a key strategy for better evaluation of the performance of tests and is also useful for the identification of technical limitations.

Amebiasis: clinical and laboratory perspectives

Entamoeba histolytica, the premier intestinal protozoan, has traversed time in its relentless quest for survival in its dichotomous role of parasite and pathogen. Enigmatic in its transition from human intestinal commensal to invader of human tissue, diverse in its pathogenicity for the human host, and intricate in its bacterial interrelationship in the bowel, E. histolytica has become the focal point of intensive investigation in its basic biology underscoring human pathogenicity. This review will focus on facets of cell biology, pathophysiology, clinical, therapeutic, and epidemiologic, correlates, along with diagnostic modalities and future research trends.

Liver abscess in the tropics: experience in the University Hospital, Kuala Lumpur

We reviewed 204 cases of liver abscess seen between 1970 and 1985. Ninety were found to be amoebic, 24 pyogenic and one tuberculous. The cause of the abscesses in the remaining 89 patients was not established. The patients were predominantly male, Indians, and in the 30-60 age group. The majority of patients presented with fever and right hypochondrial pain. The most common laboratory findings were leucocytosis, hypoalbuminaemia and an elevated serum alkaline phosphatase. Amoebic abscesses were mainly solitary while pyogenic abscesses were mainly multiple. Complications were few in our patients and included rupture into the pleural and peritoneal cavities and septicaemic shock. An overall mortality of 2.9% was recorded. The difficulty in diagnosing the abscess type is highlighted. The single most important test in helping us diagnose amoebic abscess, presumably the most common type of abscess in the tropics, is the Entamoeba histolytica antibody assay. This test should be used more frequently in the tropics.

Specific circulating immune complexes in amoebic liver abscess

A micro enzyme-linked immunosorbent assay was used to detect the presence of amoebic antigen in polyethylene-glycol-precipitated circulating immune complexes (CIC). A cutoff dilution of greater than 1:160 for the precipitates was taken to be of clinical significance. Among the patients with amoebic liver abscess, 93% (14 of 15 confirmed cases) had indications of amoebic antigen in CIC. In 57% of the suspected cases of amoebic liver abscess, amoebic antigen could be detected in CIC. The specificity of the technique for the demonstration of specific amoebic antigen is indicated by the undetectable levels of amoebic antigen in CIC in serum samples from nine cases of nonamoebic hepatic diseases and 10 apparently healthy subjects. It is thus believed that the specific diagnosis of an individual case of amoebic liver abscess can be made by demonstrating specific amoebic antigen in CIC.

A dot enzyme-linked immunosorbent assay for detection of antibodies against Entamoeba histolytica

A visual micro-dot enzyme-linked immunosorbent assay (ELISA) based on detection of antibodies against soluble antigens of axenically grown cultures of Entamoeba histolytica is described. The antigen was spotted on a nitrocellulose sheet, the unsaturated sites blocked with bovine serum albumin (BSA) and incubated with 3-fold dilutions of patient sera followed by incubation with protein A conjugated to peroxidase. Enzymic activity was evidenced using the substrate 4-chloro-1-naphthol. A positive reaction produced a blue spot. The sensitivity of the assay was better and comparable to the indirect haemagglutination assay (IHA) and plate ELISA. The entire assay could be completed within 3 h. Antigen-loaded and pre-blocked nitrocellulose strips could be stored up to 3 months at room temperature and 37 degrees C.