Patterns of Protozoan Infections: Spatiotemporal Associations with Cattle Density

Abstract

Waste from cattle production contains protozoa, such as Cryptosporidium spp. and Giardia, which can be transmitted to humans. People residing in areas of high cattle density may be at increased risk for protozoan infections. The objective of this study was to assess spatial and temporal associations between cattle density and hospitalizations for protozoan infections in the U.S. elderly. Data on protozoan infections were abstracted from Centers for Medicare and Medicaid Services datasets for a 14-year period (1991-2004). Cattle inventory data were abstracted from the 2002 U.S. Census of Agriculture. Counties were classified into one of five exposure categories based on both cattle density and human density. Our analyses considered differences in rates, trends, and variations in seasonal patterns based on exposure categories. Cryptosporidiosis demonstrated a trend of increasing annual rates related to increased potential exposure to cattle. Both cryptosporidiosis and giardiasis demonstrated significant seasonal patterns peaking during the fourth week of October in areas of high cattle/low population density and the second week of September in counties with low cattle/low human density, respectively. Counties with low human population density (regardless of cattle density) had the highest rate of all protozoan infections, peaking in the summer. These results demonstrate the elderly population is at increased risk of protozoan infections in areas of high cattle density, particularly cryptosporidiosis. The seasonal patterns and higher annual rates seen in rural areas suggest time-variant environmental exposures, which may be affected with geographical and temporal targeting of agricultural policies and interventions to improve public health.

Evolving epidemiology of reported cryptosporidiosis cases in the United States, 1995–2012

“…It cannot be determined from NNDSS data alone whether the observed changes in geographical distribution seen in this study reflect regional differences in Cryptosporidium ecology and transmission, or jurisdictional differences in the capacity to detect, investigate, or report cases. The increased reporting in the upper Midwest region could be a consequence of possible increased Cryptosporidium transmission following the 1993 Milwaukee drinking water-associated outbreak or it could be a consequence of higher cattle density in this region compared with other regions; this increased cattle density could be a proxy for increased contact with pre-weaned calves [39, 40]. Additionally, the Milwaukee outbreak in 1993 might have led to increased regional awareness of cryptosporidiosis or increased regional investment in capacity to detect, investigate, and report cases.…”

Triage and Protocol Recommendations for the Parasitology Laboratory Based on an Epidemiological Investigation of Parasite Diagnostics in Ontario Laboratories

“…Based on evidence in the literature regarding population density ( 7 , 8 ), residency of the patient was studied. Three categories were developed based on natural cut-offs: rural (population <40,000 based on the 2006 census) ( 19 ); mixed/midsized (40,000 to 100,000 and known suburban regions whose individual populations were not provided by the census); and urban (>100,000).…”

“…For locally endemic parasites, many of the risk factors and modes of transmission are similar. Key modes include contact with food or water (drinking or recreational) contaminated by feces ( 1 , 6 , 7 ), and contact with animals (farm, domestic or wildlife) ( 1 , 7 , 8 ). Consequently, living or visiting rural regions is a risk factor because both contact with animals and untreated water are more prevalent outside of urban centres ( 7 , 8 ).…”

“…Key modes include contact with food or water (drinking or recreational) contaminated by feces ( 1 , 6 , 7 ), and contact with animals (farm, domestic or wildlife) ( 1 , 7 , 8 ). Consequently, living or visiting rural regions is a risk factor because both contact with animals and untreated water are more prevalent outside of urban centres ( 7 , 8 ). Individuals who are HIV-positive, institutionalized or otherwise immunocompromised have also been found to have higher rates of infection ( 1 , 6 , 9 ).…”

Spatial Modelling Tools to Integrate Public Health and Environmental Science, Illustrated with Infectious Cryptosporidiosis

“…Infection is common in developed countries, where children <5 years old bear the greatest burden of cryptosporidiosis [ 40 , 41 , 42 ]. Positive area-level associations of disease with livestock density have been reported from New Zealand [ 43 ], the US [ 44 ] and Scotland [ 45 ], and in rural Canada [ 46 ]. There are clear differences in seasonal patterns of cryptosporidiosis across urban-rural areas and molecular evidence suggests that there is considerable potential for zoonotic transmission from cattle in rural regions [ 46 , 47 ].…”