Sensitivity of Fecal Egg Count Tests Compared

The Kato-Katz thick smear (Kato-Katz) is the recommended diagnostic method for worm infections, but is difficult to standardize and has now been compared with an alternative test, the McMaster egg counting method (McMaster).

Scientists at Ghent University, (Merelbeke, Belgium), compared the two methods for the detection of STH in 1,543 subjects resident in five countries across Africa, Asia and South America. The consistency of the performance of both methods in different trials, the validity of the fixed multiplication factor employed in the Kato-Katz method and the accuracy of these methods for estimating “true” drug efficacies were assessed.

The Kato-Katz method detected significantly more Ascaris lumbricoides infections than the McMaster method (88.1% versus 75.6%), whereas the difference in sensitivity between the two methods was nonsignificant for hookworm (78.3% versus 72.4%) and Trichuris trichiura (82.6% versus 80.3%). The sensitivity of the methods varied significantly across trials and magnitude of fecal egg counts (FEC). Quantitative comparison revealed a significant correlation in FEC between both methods, and indicated no significant difference in FEC, except for A. lumbricoides, where the Kato-Katz resulted in significantly higher FEC (14,197 eggs per gram of stool (EPG) versus 5,982 EPG). The McMaster provided more accurate efficacy results in a drug trial where the absolute difference to ‘true’ drug efficacy was 1.7% versus 4.5%.

The authors concluded that in this multinational study highlights considerable variation in the performance of two methods used for the diagnosis of STH, particularly for the commonly used Kato-Katz. Both the McMaster and the Kato-Katz methods are valid methods for monitoring large-scale treatment administration programs. Yet, the McMaster method seems more suitable for further standardization because of its robust multiplication factor, and allowing for simultaneous detection of all species of STH.

The study was published online in June 2011, in Public Library of Science Neglected Tropical Diseases.

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