A multiattribute utility evaluation of different methods for the detection of enteric protozoa causing diarrhea in AIDS patients

Abstract

Background: Enteric protozoa and sporozoa have emerged as important opportunistic parasites and can cause fatal infections in AIDS patients. The line of treatment being different for them necessitates an accurate and prompt identification of these to avoid empirical treatment. In this study which is the first of its kind from India we did a comprehensive evaluation of different techniques, comparing them on the basis of the attributes like yield, cost, time taken, expertise and infrastructure. For the first time combination of Calcoflour White and DAPI, a nuclear stain, were used to identify Microsporidia spp. Thus, a diagnostic protocol was devised for rapid, sensitive and cost effective identification of the opportunistic enteric protozoa.

Results: The organisms isolated from the stool samples of the cases (450 HIV patients) were predominantly Cryptosporidium spp., Microsporidia spp. and Cyclospora spp. Interestingly, the control group (200 relatives of the patients who were HIV negative) showed a high incidence (21%) of Cryptosporidium spp. We found a significant increase in the sensitivity of microscopy in detecting Cryptosporidium spp. and Cyclospora spp. after formol ether concentration. Kinyoun's staining was better compared to Modified safranin staining for Cryptosporidium spp. identification. Although ELISA had a sensitivity of 93.25% and specificity of 97% for Cryptosporidium spp. detection, we ranked Kinyoun's staining better than ELISA because it is not affordable to most of our patients. For detecting Cyclospora cayetanensis, autoflourescence was the easiest and most cost effective method followed by Safranin technique. Combination of Calcoflour White stain and DAPI gave good results for the identification of Microsporidia spp. We assessed the above techniques and graded the attributes in the following descending order: cost effectiveness, sensitivity, ease of use and interpretation, time taken for the procedure and batch testing.

Conclusion: Thus, we conclude that a combination of minimum three procedures should be carried out for the screening of stool specimens of HIV positive patients. Kinyoun's staining should be made mandatory for every diarrheal stool sample from HIV patients. Also every laboratory should assign its own value to the attributes and apply Multiattribute utility theory or the Analytical hierarchy process to decide the most appropriate methodology.

Figure 1

Microsporidia spores stained with the combination of Calcoflour White and DAPI.