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Laboratory Diagnosis

Acute bacillary dysentery can be diagnosed by identifying dysentery bacilli in the stools with an associated inflammatory cellular exudate. This is characterized by desquamated intestinal epithelial cells, blood, mucus, refractile macrophages, and neutrophils. The macrophages sometimes resemble trophozoites of Entamoeba histolytica. Small amounts of blood-tinged mucus or pus from a fresh stool or fresh material collected via a proctoscope or rectal swab should be used for microscopic examination and culture; any Shigella thus isolated can be identified and typed. The patient's white blood cell count may be 15,000 or higher, with predominance of neutrophils early in the disease.

Serological diagnosis may help in convalescent or chronic bacillary dysentery, where high titer agglutinations may sometimes be obtained. However, positive agglutination tests can occur in normal healthy persons who have never had bacillary dysentery, and patients who have recovered from the disease may show negative agglutination tests. Thus, too much reliance should not be placed on the initial titer, but variation during the course of an illness may be significant.

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