During 2012, 346 cases of cryptosporidiosis (6.5 per 100,000 population) were reported. This is 45% higher than the median number of cases reported annually from 2002 to 2011 (median, 239 cases; range, 147 to 389). The median age of cases in 2012 was 27 years (range, 3 months to 92 years). Children 10 years of age or younger accounted for 30% of cases. Fifty-eight percent of cases occurred during July through October. The incidence of cryptosporidiosis in the Southwestern, Southeastern, Central, and West Central districts (20.8, 19.7, 10.8, and 9.4 cases per 100,000, respectively) was significantly higher than the statewide incidence. Only 52 (15%) reported cases occurred among residents of the metropolitan area (1.7 per 100,000). Thirty-seven (11%) cases required hospitalization, for a median of 4 days (range, 1 to 26 days).
A record 18 outbreaks of cryptosporidiosis were identified in Minnesota in 2012, accounting for 58 laboratory-confirmed cases (7 among non-Minnesota residents). Nine recreational water outbreaks of cryptosporidiosis occurred, accounting for 181 cases (42 laboratory-confirmed). The recreational water outbreaks included three at municipal pools/ water parks (Goodhue, Hennepin, and Lyon counties), two at hotel water parks (Crow Wing and St. Louis counties), two at splash pads (Benton and Stearns counties), one at a lake (Crow Wing County), and one at a swim pond (Washington County). Three outbreaks of cryptosporidiosis were associated with contact with calves, accounting for 44 cases (9 laboratory-confirmed). The animal contact outbreaks occurred at a petting zoo (Goodhue County), an educational farm camp (Hennepin County), and a birthday party held at a private farm (Dakota County). Six outbreaks of cryptosporidiosis at daycares accounted for 20 cases (7 laboratory-confirmed); the daycare outbreaks occurred in Brown, Goodhue, Mower, Olmsted, Ramsey, and Stearns Counties.
In a paper published in Clinical Infectious Diseases in April 2010, we reported an evaluation of rapid assays used by Minnesota clinical laboratories for the diagnosis of cryptosporidiosis. The overall positive predictive value of the rapid assays was 56%, compared to 97% for non-rapid assays. The widespread use of rapid assays could be artificially contributing to the increased number of reported cases of cryptosporidiosis. Rapid assay-positive specimens should be confirmed with other methods. It is important that health care providers are aware of the limitations and proper use of rapid assays in the diagnosis of cryptosporidiosis and that they limit testing to patients who have symptoms characteristic of the disease.
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