*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2002
Shigellosis is a bacterial disease transmitted by the fecal-oral route, usually through hands contaminated with feces. It can also be transmitted through contaminated food and water or through oral-anal sex practices. Shigellosis is highly communicable, as only 10-100 organisms must be ingested to establish infection. Shigella bacteria infect only humans.
In 2002, 138 cases of shigellosis were reported in Indiana, for a case rate of 2.2 per 100,000 population (Table 1). This represents a significant decrease from the incidence rate (4.1) in 2001. This is the second consecutive year since 2000 that the incidence of shigellosis infection has decreased. Figure 1 shows the number of reported cases per year for
1998-2002. The incidence of shigellosis peaked during the summer months (Figure 2). As shown in Figure 3, age-specific rates were highest among preschoolers aged 1-4 years (9.3), followed by children aged 5-9 years (4.3), and infants (3.5). These high age-specific rates of shigellosis among preschool-aged and elementary school-aged children represent the increasing problem of shigellosis outbreaks in daycare centers and certain elementary school grades. Females (2.4) were more likely to be reported than males (2.1). The rate of illness among blacks was 5.0, almost four times higher than whites (1.3) and almost twice the rate for other races (2.6).
The incidence rates were highest among the following counties reporting five or more cases:
Carroll (39.6), Allen (8.0), and Lake (5.5). Figure 4 shows Indiana counties reporting five or more cases.
There are four species of Shigella bacteria. In 2002, the serotype was determined for 110 (80%) of the 138 reported shigellosis cases. Shigella sonnei is the most common serotype isolated in the United States and accounted for 94 (85%) of the serotyped cases. Shigella flexneri is isolated less frequently and is usually related to exposures outside of the U.S. This serotype was isolated from 11 cases (10%). Shigella boydii is rarely found in the U.S. and accounted for two cases (2%). Shigella dysenteriae, a serotype that can cause severe infection, is extremely uncommon in the U.S. and is almost always associated with exposures outside of the U.S. Three Shigella dysenteriae cases (3%) were identified (see below).
One outbreak of shigellosis occurred in 2002 in Bartholomew County. Three confirmed cases of Shigella dysenteriae were identified in residents of Bartholomew, Jennings, and Brown Counties. Although this strain is extremely rare in the U.S., all three cases had identical serotype and DNA fingerprint patterns, strongly suggesting a common source. None of the cases reported recent overseas travel, but all three did report recently eating at the same Bartholomew County restaurant. The investigation revealed that a restaurant employee reported recent travel to a country where S. dysenteriae is common and became ill with a compatible illness on the return trip to the U.S. This employee did work while ill. Exclusion policies for ill employees and proper hand-washing and hygiene measures were reviewed with restaurant staff.