COMPARISON OF SEQUENTIAL, RANDOM, AND HEMACYTOMETER METHODS FOR COUNTING CRYPTOSPORIDIUM OOCYSTS

In animal and clinical studies of Cryptosporidium infection, counting Cryptosporidium oocysts in collected fecal samples is often critical t o interpretation of results and validity of statistical analyses. In t his experiment, 3 methods of counting oocysts derived from feces of in fected mice were compared. These included sequential counting of oocys ts in 25 adjacent microscopic fields, random counting of oocysts in 25 scattered microscopic fields, and hemacytometer counting of oocysts u sing standard procedures. Numerical results are expressed as the numbe rs of oocysts per microscopic field for sequential and random counting methods or per mu l for the hemacytometer method. Our results showed that the numbers of oocysts adjusted for volume and weight, or for vol ume alone, were similar for all 3 techniques. Linear relationships bet ween the 3 methods allow use of linear regression to convert the numbe r of oocysts counted by 1 method into those counted by another. This s uggests that comparisons between different experiments in which Crypto sporidium oocysts are counted using any of these methods are both poss ible and valid.