Comparison of polymerase chain reaction, immunochromatographic assay and staining techniques in diagnosis of cryptosporiodiosis

ABSTRACT

Cryptosporidiosis represents a major health problem worldwide. In developed countries, massive outbreaks have been reported while in developing countries, it is associated with significant morbidity and mortality, especially among infants and children. Although the modified acid-fast technique is the commonly used slain for its detection, its sensitivity and specificity appeared to be rather low. The present study aimed at comparing the conventional diagnostic method with the recent techniques namely immunochromatographic [ICT] strip assay and multiplex allele specific polymerase chain reaction [MAS-PCR]. The second objective was to genotype the diagnosed isolates using MASPCR. Seventy six immunocompromised patients having acute or chronic diarrhea were selected from the attendance of the pediatrics, oncology and nephrology clinics in Suez Canal University Hospital. Cryptosporidiosis was diagnosed by Kinyoun acid fast stain, ICT strip assay and MAS-PCR. Samples proved positive for cryptosporidiosis were genotyped using MAS-PCR. Using MAS-PCR as Gold standard method, modified Kinyoun acid fast stain and ICT strip showed sensitivity [79 vs 89%], specificity [98 vs 100%], positive predictive value [94 vs 100%], negative predictive value [93 vs 100%] and diagnostic accuracy [88.5 vs 94.5%]. Using MAS-PCR for genotyping, C. parvum comprised the majority [68.4%] of cases while C. hominis was only 26.3%. Only one patient had mixed genotype infection. C. parvum infections were associated with low intensity of oocyst shedding while C hominis infections were with high intensity of oocyst shedding. The agreement between microscopy and MAS-PCR results proved that only 60% of positive cases identified as C. hominis [type 1] by MASPCR were positive by microscopy while, 92.3% of C. parvum [type II] positive cases by MAS-PCR were positive by microscopy. The agreement between ICT strip and MAS-PCR results proved that the strip identified 100% of positive cases of C. hominis [type I] and 84.6% of C. parvum [type II] positive cases by MAS-PCR. The ICT strip assay gave very good results regarding performance and came second to MASPCR in ranking which has an additional advantage due to its ability to genotype diagnosed isolates. The low sensitivity of staining method and high cost of MAS-PCR recommend the ICT strips for the wide use especially in field of diagnosis and in outbreaks where large number of tests needs to be performed in a short period of time