Comparação entre os métodos de Ziehl-Neelsen modificado e Acid-Fast-Trichrome para a pesquisa fecal de Cryptosporidium parvum e Isospora belli / Comparison between the modified Ziehl-Neelsen and Acid-Fast-Trichrome methods for fecal screening of Cryptosporidium parvum and Isospora belli

RESUMO

Due to the importance of Cryptosporidium parvum, Cyclospora cayetanensis and Isospora belli as opportunistic parasites, it is essential for laboratories to morphologically differentiate these coccidia. Among the recommended methods for diagnosis of C. parvum and I. belli is the Modified Ziehl-Neelsen stain (MZN) and recently a new technique, the Acid-Fast-Trichrome (AFT) was proposed. The purpose of this study was to compare the AFT and MZN techniques regarding the detection of C. parvum and I. belli oocysts in stool samples of HIV-positive patients. According to the presence (n=60) or absence of diarrhea (n=60), two groups were selected for inclusion in this study. The stool samples were collected in 10 formalin solution and the pellets, obtained without and after centrifugation-concentration (500xg; 10 min), were submitted to both stain techniques. Considering the positivity of the techniques (AFT and MZN), we observed the superiority of MZN stain (n=19; 100 positive cases) over AFT (n=8; 42.1). The identification of the 101 truly-negative cases was possible with both techniques, but when the AFT stain was used, the oocysts showed a variable inner stain degree, which resulted in false-negatives. Enteric coccidiosis was more frequent among the patients who presented diarrhea (26.6) compared to asymptomatic individuals (5); C. cayetanensis was not detected in these groups. We were interested in evaluating the employment of AFT for the Cyclospora oocyst stain. Based on the sensitivity and specificity obtained in this study (100), we concluded that the MZN technique is still the most indicated for routine use in clinical analysis laboratories, for the diagnosis of cryptosporidiosis and isosporosis, especially when it was used together with the centrifugation procedure (500xg; 10 min). Our results showed that with some improvements, AFT would be a simple and inexpensive technique appropriate for use in the diagnosis of intestinal coccidia (C. parvum, C. cayetanensis and I. belli). It can also be extended to the detection of microsporidia.