BACKGROUND: Cryptosporidiosis is an acute diarrheal illness caused by the protozoan Cryptosporidium. Numerous species/genotypes have been identified, but C. hominis and C. parvum are by far the most commonly associated with human illness. Risk factors for infection vary by species/genotype. Molecular methods are necessary to distinguish species of Cryptosporidium. In 1999, the Minnesota Department of Health (MDH) began developing molecular subtyping for Cryptosporidium to enhance outbreak detection and strengthen understanding of the pathogen.
METHODS: Since 2006, clinical laboratories in Minnesota have been required to submit clinical materials from Cryptosporidium-positive specimens to MDH. Genotyping was performed by PCR followed by restriction fragment length polymorphism analysis of either the dihydrofolate reductase gene or the small-subunit rRNA gene. We examined the epidemiology of cases of cryptosporidiosis caused by species/genotypes other than C. hominis or C. parvum (rare species) in Minnesota from 2007-2016.
RESULTS: From 2007-2016, 96 cases of eight rare species of Cryptosporidium were identified from human clinical specimens in Minnesota; C. ubiquitum (n=45), C. sp. chipmunk genotype I (n=25), C. felis (n=10), and C. sp. deer mouse genotype III (n=8) were most commonly identified. Cases of rare species increased >1200% in the 10-year period, with a median of 7.5 cases identified annually (range, 3 to 38). Demographic and illness characteristics of rare species cases were similar to C. hominis and C. parvum cases; however, C. sp. chipmunk genotype I and C. felis cases were more likely to be male (p=0.01; p=0.04) and C. ubiquitum cases female (p=0.03). C. felis cases also tended to be older (p=0.01). Eight (8.4%) rare species cases reported an immunocompromising condition. Most (85%) specimens were collected during July-October. Specimens identified as rare species at MDH were initially tested using a variety of methods at the clinical laboratory; of specimens that tested positive by multiplex PCR, 13.1% yielded rare species (compared to 4.7% for other tests). Two outbreaks due to rare species were identified (C. ubiquitum and C. sp. chipmunk genotype I), both associated with swimming pools.
CONCLUSIONS: The identification of species/genotypes other than C. hominis or C. parvum increased dramatically during the past 10 years in Minnesota, predominantly in healthy individuals. The use of multiplex PCR panels appears to be escalating the increase. This study further emphasizes the value of performing molecular characterization of Cryptosporidium specimens, which may better inform case follow-up.