Cryptosporidiosis, 2014

During 2014, 337 cases of cryptosporidiosis (6.2 per 100,000 population) were reported. This is 11% higher than the median number of cases reported annually from 2004 to 2013 (median, 304.5 cases; range, 147 to 389). The median age of cases in 2014 was 24 years (range, 9 months to 99 years). Children 10 years of age or younger accounted for 29% of cases. Sixty-one percent of cases occurred during July through October. The incidence of cryptosporidiosis in the West Central, Southwestern, Northeastern, Southeastern, and Northwestern districts (25.3, 12.8, 11.3, 11.2, and 10.7 cases per 100,000, respectively) was significantly higher than the statewide incidence. Only 70 (21%) cases occurred among residents of the metropolitan area (2.4 per 100,000). Forty-five (13%) cases required hospitalization, for a median of 4 days (range, 2 to 13 days).

Seven outbreaks of cryptosporidiosis were identified in Minnesota in 2014, accounting for 22 laboratory-confirmed cases. One recreational water outbreak occurred at a swim school in Hennepin County, accounting for 3 cases (all laboratory-confirmed). Three outbreaks of cryptosporidiosis were associated with contact with calves, accounting for 23 cases (9 laboratory-confirmed). The animal contact outbreaks were associated with a home farm (Itasca County), a veterinary technician class farm visit (Hennepin County), and a preschool class farm visit (Olmsted County). Three outbreaks of cryptosporidiosis at daycares accounted for 20 cases (10 laboratory-confirmed); the daycare outbreaks occurred in Becker, Douglas, and Watonwan 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. This suggests that widespread use of rapid assays could be artificially contributing to the increased number of reported cases. In 2014, 251 (74%) patients were positive for Cryptosporidium by a rapid assay conducted in a clinical laboratory. However, 60 (27%) of the 219 specimens received at the PHL could not subsequently be confirmed by polymerase chain reaction or direct fluorescent antibody test. 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.

• For up to date information see>> Cryptosporidiosis (Cryptosporidium spp.)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2014