During 2001, 493 culture-confirmed cases of Shigella infection (10.0 per 100,000 population) were reported (Figure 1). This represents a 45% decrease from the 904 cases reported in 2000 (the largest number of Shigella cases ever reported in Minnesota) and a 68% increase from the median number of cases reported annually from 1997 to 2000 (median, 293 cases; range, 138 to 904).
In 2001, Shigella sonnei accounted for 450 (93%) cases, S. flexneri for 29 (6%), S. dysenteriae for three (1%), and S. boydii for two (<1%); nine isolates were not serotyped. Case-patients ranged in age from 1 month to 84 years (median, 10 years). Fifty-one percent of case-patients were less than 10 years of age; children less than 5 years of age accounted for 30% of cases. Seventy-six (15%) cases were hospitalized. Fifty-five percent of all Shigella cases resided in the seven-county Twin Cities metropolitan area, including 31% in Hennepin County and 9% in Ramsey County. The shigellosis incidence rates in the Northwestern and Southwestern districts (31.6 and 27.0 cases per 100,000 population, respectively) were significantly higher than those statewide. Community outbreaks, primarily outbreaks among children in elementary schools, accounted for the high rates of shigellosis in these two districts. The Southeastern district had the lowest rate of shigellosis (2.4 per 100,000 population).
Twenty-five outbreaks of shigellosis were identified in 2001; all were due to S. sonnei. These outbreaks resulted in at least 280 illnesses, including 165 culture-confirmed cases (representing 37% of reported S. sonnei cases). The outbreaks occurred in a variety of settings, including child daycare centers and homes (18 outbreaks) and elementary schools (six outbreaks).
Every tenth isolate of Shigella received at MDH was tested for antimicrobial resistance, but only one isolate was included from each outbreak. Forty-six isolates were tested in 2001. Resistance to ampicillin decreased from 94% of isolates in 2000 to 83% in 2001, while resistance to trimethoprim-sulfamethoxazole increased from 10% of isolates in 2000 to 22% in 2001. The percentage of isolates that were resistant to both ampicillin and trimethoprim-sulfamethoxazole increased from 6% in 2000 to 15% in 2001.