Relative importance of the various environmental sources of Cryptosporidium oocysts in three watersheds

This study was conducted to guide the prioritisation of efforts to manage Cryptosporidum contamination of drinking water supplies in Trinidad, W.I. The main objective was to investigate the relative importance of three main types of sources of Cryptosporidium oocysts: urban, agriculture and wildlife. Weekly surface water samples were collected from 19 sites distributed among three watersheds, and examined for the presence of oocysts. A stratified random sampling design was used with each watershed representing one of the three main sources of oocysts listed above. Results showed a significant association between watershed and the occurrence of positive samples (chi(2)=16.523, d.f. =2, p = 0.000), indicating that land use influenced the presence of oocysts. Urban and forested lands were the two most important sources of oocysts. There was no apparent association between agriculture and the presence of oocysts, and there was no significant difference between the percentage of positive samples at sites below agricultural facilities and sites not associated with agriculture within a single watershed (chi(2)=2.45, d.f. =1, p = 0.117). We conclude that urban and wildlife are the main types of sources of Cryptosporidium contamination of surface water, whereas the contribution of agriculture is minor.