Tennessee Grapples With Cryptosporidiosis Surge

Farmers’ Markets and Daycares Cited in Spreading Parasitic Illness

Tennessee has seen a significant number of cryptosporidiosis cases between 2018 and 2023, with over a thousand identified. This parasitic infection, often spread through contaminated water or contact with animals, highlights ongoing public health challenges in the state.

Understanding the Spread

A total of 1174 cryptosporidiosis cases were reported in Tennessee from 2018 to 2023, resulting in an average rate of 2.8 cases per 100,000 residents. Of these, 4.2% were linked to identified outbreaks. Four such outbreaks occurred during this period: a 2018 restaurant-linked event, a 2021 splashpad incident, and two separate daycare outbreaks in 2022 and 2023, attributed to person-to-person transmission of specific parasite genotypes.

Laboratory confirmation played a key role, with 92% of all reported cases testing positive for Cryptosporidium. However, species or genotype information was only available for a fraction of these cases, underscoring a need for more detailed diagnostic tracking. Polymerase chain reaction (PCR) was the most common diagnostic method, used in 65% of laboratory-confirmed infections.

Demographic and Exposure Patterns

Females accounted for 55% of all cases. The age distribution showed that 32% of affected individuals were under 18, 54% were between 18 and 64, and 14% were 65 or older. The majority of cases, 83%, reported White race. Animal contact was a significant factor, reported by 54% of individuals, with visiting or living on a farm (20%) and pet ownership (9%) being the most common exposures.

Municipal water sources were implicated in 67% of cases, while well water was reported by 8%. International travel and contact with individuals experiencing diarrheal illness were reported in 6% and 9% of cases, respectively. These exposure patterns remained consistent whether or not specific genotype results were available.

Species-Specific Insights

Among cases with identified species, C. small was the most prevalent (65%), followed by C. man (21%). C. Felis and C. ubiquitum were also detected, though at lower rates. The distribution of C. small cases was higher in rural counties, whereas C. man cases were more concentrated in urban areas. Children under 18 represented a significant portion of C. small (54%) and C. ubiquitum (80%) infections.

Individuals infected with C. small were more likely to report drinking well water and having contact with farm animals, including goats, cows, and chickens. In contrast, C. man infections were more frequently associated with recreational water exposure, both in natural and treated bodies of water, and with direct contact with other sick individuals.

Genotype Associations

For cases with genotyping, C. small accounted for 74% of the identified subtypes. Common C. small subtypes, such as IIaA15G2R1, showed a strong association with animal exposure, particularly to goats, cows, or chickens, and visiting farms or zoos. These findings are consistent with broader trends showing that animal-related activities are a significant risk factor for cryptosporidiosis. For example, a 2023 study in the UK found that over half of cryptosporidiosis cases were linked to animal contact, particularly with cattle and sheep (UK Health Security Agency).

Conversely, the most frequently identified C. man subtypes, IfA12G1R5 and IdA17G1, did not show specific associations with the assessed exposure variables when compared to the general population.