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much like febrile seizures, except that they may occur in children with no or only low-grade fever and are prominent in children beyond the usual age of susceptibility to febrile seizures (2 to 3 years of age). Shigella bacteremia is more common than previously believed (especially with infection due to S. dysenteriae 1), has been detected in about 4 percent of patients with shigellosis admitted to the International Centre for Diarrhoeal Disease Research hospital in Bangladesh (ICDDR,B); and is associated with increased mortality (Struelens et al., 1985). Denudation of the intestinal epithelium increases the likelihood of gram-negative sepsis with other Enterobacteriaceae, especially in malnourished children, and has been documented in another 4 percent of hospitalized patients in Dhaka, Bangladesh. Denudation also dramatically increases the mortality rate.

Infection due to S. dysenteriae 1, and to a lesser extent S. flexneri, is associated with the development of a leukemoid reaction in 4 percent of hospitalized patients with shigellosis. Of these, one-third have evidence of hemolysis, one-third develop a hemolytic-uremic syndrome, and a few have transient uremia alone (Butler et al., 1984). The mortality rate for those with uncomplicated or complicated leukemoid reactions is about 20 percent. Bacteremia, leukemoid reactions, and hemolytic-uremic syndrome occur most often in poorly nourished children infected with S. dysenteriae 1, and are therefore more common in developing countries. Reactive arthritis with or without other classical manifestations of Reiter’s syndrome occurs more frequently with some types of shigella (e.g., S. flexneri) and is often seen in individuals positive for HLA-B27 histocompatibility antigen (Keusch, 1982).

PATHOGEN DESCRIPTION

Shigellas are classified in the family Enterobacteriaceae, tribe Escherichieae, and are closely related to E. coli. They are nonmotile, rod shaped, gram-negative bacteria that ferment glucose but do not produce gas. They are usually recognized first by their inability to ferment lactose, although S. sonnei is capable of late lactose fermentation. Selective media are employed for this purpose; these media contain bile salts to inhibit the growth of other fecal organisms and a dye indicator to demonstrate lactose fermentation. Although many media have been devised, some are highly inhibitory to shigellas, especially to S. dysenteriae 1. The genus is subdivided into four species, dysenteriae, flexneri, boydii, and sonnei. These have antigenically distinct lipopolysaccharides and may be recognized through the use of grouping antisera, as well as by biochemical reactions. There are multiple subtypes of S. dysenteriae, flexneri, and boydii and multiple colicin types of S. sonnei. Generally, however, a limited number of subtypes prevail in any given geographic area. Two major virulence attributes are involved in pathogenesis: the ability to invade epithelial cells, which is under polygenic control, and toxin production, the genetics of which are still uncertain.



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