Shigella serogrouping antisera from six companies (Becton Dickinson, Denka, Difco, Murex, Roach, and Sanofi-Pasteur) intended for the slide agglutination test and those of the Wellcolex Colour Shigella latex agglutination test were evaluated to identify quality products for Shigella identification. Forty-six reference Shigella strains (one for each serotype and species), 50 clinical strains (21 S. flexneri, 21 S. sonnei, 4 S. dysenteriae, 4 S. boydii) representing the most prevalent species and serotypes encountered in Quebec, and 9 non-Shigella strains were tested according to the manufacturers' instructions. A 3؉ reaction (>75% agglutination) was considered positive for the slide agglutination tests. Sensitivity varied from 47% (Roach) to 94% (Difco). For the 105 strains tested, accuracy ranged from 53% (Roach) to 91% (Wellcolex). Specificity varied from 97 to 100% for group A antisera, from 96 to 100% for group B antisera, from 88 to 100% for group C antisera, and from 95 to 99% for group D antisera. The costs of reagents required to test one strain varied from $3.50 to $13.20 (in Canadian dollars). In conclusion, Roach reagents proved to be unsatisfactory for Shigella serogrouping. Among those from the remaining companies, the Denka, Difco, and Wellcolex reagents met a performance standard of 90% accuracy. Shigella species are primarily responsible for gastrointestinal tract infections ranging from bacillary dysentery to less acute infections and are spread worldwide (1, 9-11, 13, 14). They share common characteristics with members of the genus Escherichia, from which they cannot be differentiated by DNA-DNA hybridization. According to modern taxonomy, subdivision of the genus into species is irrelevant. Nonetheless, medical and epidemiological interests justify maintaining the genus with its four species: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei, also known as groups A, B, C, and D, respectively. These are subdivided into serotypes, which are given numerical designations (5-7, 13). Laboratory diagnosis relies on the isolation of the organism from feces and its identification by means of cultural and biochemical characteristics. Serological identification is mandatory because of its close relatedness to Escherichia coli. It requires, for a start, that species be identified (serogrouping); this is followed by serotype determination (serotyping). Serogrouping is generally carried out in clinical laboratories, while serotyping is performed in central or reference laboratories (5, 6, 13). Serogrouping is based on the detection of somatic O antigens by an agglutination technique with polyclonal antisera specific to each of the four Shigella species. Unfortunately, there is no international consensus on the choice of Shigella strains for the production of the grouping antisera (6). These antisera are commercially available from various manufacturers, but the sensitivities and specificities of these products remain to be determined. A study conducted by the U.S. Centers for Disease Control in 1988 (4) s...
