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Participatory probabilistic assessment of the risk to human health associated with cryptosporidiosis from urban dairying in Dagoretti, Nairobi, Kenya


We carried out a participatory risk assessment to estimate the risk (negative consequences and their likelihood) from zoonotic Cryptosporidium originating in dairy farms in urban Dagoretti, Nairobi to dairy farm households and their neighbours. We selected 20 households at high risk for Cryptosporidium from a larger sample of 300 dairy households in Dagoretti based on risk factors present. We then conducted a participatory mapping of the flow of the hazard from its origin (cattle) to human potential victims. This showed three main exposure pathways (food and water borne, occupational and recreational). This was used to develop a fault tree model which we parameterised using information from the study and literature. A stochastic simulation was used to estimate the probability of exposure to zoonotic cryptosporidiosis originating from urban dairying. Around 6 % of environmental samples were positive for Cryptosporidium. Probability of exposure to Cryptosporidium from dairy cattle ranged from 0.0055 for people with clinical acquired immunodeficiency syndrome in non-dairy households to 0.0102 for children under 5 years from dairy households. Most of the estimated health burden was born by children. Although dairy cattle are the source of Cryptosporidium, the model suggests consumption of vegetables is a greater source of risk than consumption of milk. In conclusion, by combining participatory methods with quantitative microbial risk assessment, we were able to rapidly, and with appropriate ‘imprecision’, investigate health risk to communities from Cryptosporidium and identify the most vulnerable groups and the most risky practices.

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  1. Appropriate imprecision: not gathering data with more accuracy than is needed to understand the priority issues for evaluation (Chambers 1983)

  2. We used the commercial MeriFluor™ Cryptosporidium/Giardia from Meridian Diagnostics, Ind., and Cincinnati, Ohio according to the manufacturer’s protocol.


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The authors wish to thank the International Research Development Centre for funding this work under the grant 103075-001. We also thank all the members of the Dagoretti agricultural and livestock extension team and all the members of the Dagoretti community who took part in this study.

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Correspondence to Delia Grace.

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This paper is part of a special supplement on assessing and managing urban zoonoses and food-borne disease in two African cities (Nairobi, Kenya and Ibadan, Nigeria).

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Grace, D., Monda, J., Karanja, N. et al. Participatory probabilistic assessment of the risk to human health associated with cryptosporidiosis from urban dairying in Dagoretti, Nairobi, Kenya. Trop Anim Health Prod 44, 33–40 (2012).

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  • Urban dairying
  • Cryptosporidium
  • Participatory risk assessment
  • Nairobi
  • Ecohealth