Characterization of Shiga Toxin-Producing E. coli Infections and Cryptosporidiosis in South Dakota with Respect to Animal Exposures, 2012

BACKGROUND:  Shiga-toxin producing strains of Escherichia coli (STEC) and Cryptosporidium spp. are significant causes of illness in humans.  Incidence rates of these illnesses are higher in South Dakota than in the United States as a whole.  Transmission of these agents to people through direct contact with animals has been identified as one of the many possible routes of exposure.  Ruminant animals may act as sub-clinical carriers of STEC, while young ruminants with clinical signs of diarrhea are common sources of zoonotic strains of Cryptosporidium.

METHODS:  Patients reported with either STEC or cryptosporidiosis in South Dakota in 2012 were interviewed regarding 7 categories of animal exposure in the days prior to illness: 1) Petting zoo/fair attendance, 2) animal event/rodeo attendance, 3) feed/pet store visits, 4) farm visits, 5) employment or residence at a farm, 6) residence with pets, and 7) visiting other households with pets.

RESULTS: Fifty (50) cases of STEC infections were identified.  A high proportion of those cases (78.0%) reported animal exposure prior to illness onset.  Living with pets was the most commonly reported animal exposure (63.6%), followed by visiting other households with pets (35.3%), and living or working on a farm (23.3%).  People who reported visiting a farm had a high level of direct animal contact and infrequently practiced personal protective measures. One hundred fifteen cases of cryptosporidiosis were identified.  Animal exposures were reported by 87.8% of those cases, with living with pets the most commonly reported exposure (63.7%), followed by living or working on a farm (45.6%), and visiting a farm (29.0%).  Those with farm exposure reported a high degree of direct contact with animals and inconsistent use of personal protective measures such as hand washing.  Cryptosporidiosis patients were significantly more likely than STEC patients to have lived or worked on a farm or attended an animal event in the days prior to their illness, and were older on average.  STEC cases were more likely to occur in the Sioux Falls area, with cryptosporidiosis more prevalent in northeastern South Dakota. Visitors to farms had a high degree of animal contact and poor adoption of personal protective practices.

CONCLUSIONS:  Patients with these illnesses had high rates of animal contact prior to illness.  Animal contact on farms emerged as an important exposure route.  Further study and educational messages targeting farm visitors should be considered to raise awareness of and better understand the role of animal contact in these illnesses.