Cryptosporidium is an enteric pathogen that is transmitted through animal-to-person or person-to-person contact or through ingestion of contaminated water or food. In the United States, Cryptosporidium affects an estimated 750,000 persons each year; however, only approximately 11,000 cases are reported nationally (1,2). Persons infected with Cryptosporidium typically develop symptoms within 2 to 10 days after exposure. Common symptoms include watery diarrhea, abdominal cramps, nausea, vomiting, or fever, which can last 1 to 2 weeks. Cryptosporidiosis is a nationally notifiable disease in the United States. Nebraska presents a unique setting for the evaluation of this pathogen because, compared with other states, Nebraska has a greater reliance on agriculture and a higher proportion of the population residing and working in rural communities. Cryptosporidium species and subtypes are generally indistinguishable using conventional diagnostic methods. Using molecular characterization, Nebraska evaluated the genetic diversity of Cryptosporidium and found a dichotomy in the distribution of cases of cryptosporidiosis caused by Cryptosporidium parvum and Cryptosporidium hominis among rural and urban settings. Characterizing clusters of C. hominis cases revealed that several child care facilities were affected by the same subtype, suggesting community-wide transmission and indicating a need for effective exclusion policies. Several cases of cryptosporidiosis caused by non–C. parvum or non–C. hominis species and genotypes indicated unique animal exposures that were previously unidentified. This study enhanced epidemiologic data by validating known Cryptosporidium sources, confirming outbreaks, and, through repeat interviews, providing additional information to inform cryptosporidiosis prevention and control efforts.

During September 2015–December 2017, a total of 630 Cryptosporidium-positive stool specimens were reported to public health agencies by clinical laboratories, which most commonly used culture independent diagnostic testing (CIDT) and enzyme immunoassays (EIAs) for detection; among these 630 positive stool specimens, 149 (24%) were sent to the Nebraska Public Health Laboratory (NPHL), and subsequently to CDC, where genotyping was conducted using nested polymerase chain reaction–restriction fragment length polymorphism analysis and DNA sequencing of the 18S rRNA gene and the gp60 gene (3,4). Epidemiologic data on cases with genotyped and subtyped Cryptosporidium stool specimens were exported from the Nebraska Electronic Disease Surveillance System and linked to molecular data to assess association among species and exposures. Odds ratios (ORs), p-values, and 95% confidence intervals (CIs) were calculated using SAS statistical software (version 9.4; SAS Institute). ArcGIS was used to map cases to depict geographic distribution of cases.

Among 149 patients with a molecularly characterized stool specimen, the median age was 22 years (range = 7 months–79 years); 79 (53%) patients were female. Eight patients (5%) were hospitalized, and no deaths were reported. Species and genotypes were identified in 149 submitted specimens, 80 (54%) of which were positive for C. hominis and 58 (29%) for C. parvum. Other identified species and genotypes included Cryptosporidium chipmunk genotype I and Cryptosporidium felis (three each); Cryptosporidium ubiquitum (two); and Cryptosporidium canis, Cryptosporidium melargridis, and Cryptosporidium skunk genotype (one each).

The 149 patients reported various exposures; 81 (54%) reported animal exposures, including 32 (40%) who reported exposure to dogs, 26 (32%) who reported exposure to cats, and 23 (28%) who reported exposure to cattle (Figure 1). Follow-up interviews identified specific dog, squirrel, and skunk exposures that previously had not been not mentioned. Overall, 11 C. hominis cases were associated with outbreaks. Three outbreaks were identified with the same C. hominis subtype within multiple child care facilities: 1) the first involved two cases, one each in two different facilities located in two distant local health department jurisdictions; 2) the second involved three cases, one case and two cases, respectively, in two child care facilities located in two neighboring local health department jurisdictions; and 3) the third involved six cases at one child care facility that is located within two adjoining local health department jurisdictions. C. parvum was associated with two outbreaks; however, only one stool specimen was sent to CDC.

Patients with C. parvum infection were more likely to report exposure to dogs and cattle than were those infected with other species. Patients with C. hominis infection were approximately nine times more likely to have reported a day care or child care exposure than were patients infected with other species (Table). Potential associations among species and recreational water exposure were also examined, but not found to be significant.

Reported cases were mapped by county of patient residence to document the urban and rural distribution of C. hominis cases and C. parvum cases in the state. C. hominis cases were identified among patients from more highly populated urban counties (nearly half of C. hominis cases were reported from Douglas County, the most populous county), whereas C. parvum cases were identified among cases from more sparsely populated rural counties (Figure 2).