Negative staining method with nigrosin for the detection of cryptosporidial oocysts: a comparative study

A comparison was made between two methods for the detection of cryptosporidial oocysts in human faecal sediments of formalin-ether concentrates: a cover-slipped, wet method (containing Gram's iodine) and an air-dried, negative staining method using nigrosin solution. A modified Ziehl-Neelsen technique was used as a reference method. The negative staining method with nigrosin gave a positive diagnosis more often than the cover-slipped wet method. A comparison of the nigrosin method with the modified Ziehl-Neelsen method gave almost identical results. Restaining the nigrosin slides with the modified Ziehl-Neelsen technique showed that the round, refractile bodies were cryptosporidial occysts.