Animal Waste, Water Quality and Human Health

Indicators, sanitary surveys and source attribution techniques 339Case Study 1 Drinking-water quality: genotyping of Cryptosporidium leads to theidentification of the source of contamination 4BackgroundIdentification of Cryptosporidium in treated drinking-water has relied onimmunofluorescence microscopic detection of oocysts in water specimens at treatmentplants. Positive findings indicate the presence of oocysts but cannot determine thespecies or subspecies. A dilemma arises when oocysts of Cryptosporidium aredetected in finished water at the treatment plant but it is not known if those oocystsarise from a species known to infect humans. If the oocysts are potentially infectiousfor humans swift action should be taken to protect public health and prevent anoutbreak. If the oocysts are, however, potentially non-infectious for humans, actionssuch as a boil-water alert could be expensive, inconvenient and unnecessary. Theapplication of molecular methods to identify species and genotypes, although timeconsuming and expensive, can prevent unnecessary alarm and enormous costs to thecommunity and the water utility. This application, in conjunction with otherobservations, provides the evidence to identify organisms with the potential to causeinfections in the human population and identify the probable source of those speciesand genotypes.ProblemIn the area of Northamptonshire, England approximately 250,000 people receive tapwater from the Anglian Water Company. In July 2008 an outbreak ofcryptosporidiosis was linked to contaminated tap water. On 23–24 June 2008Cryptosporidium spp. oocysts were detected by direct immunofluorescence antibody(DIA) microscopy as part of routine operational monitoring of treated water at asurface water treatment works. Cryptosporidium oocysts were also detected by DIAmicroscopy from the bowel contents of a rabbit carcass removed from a tank at thewater treatment works. The positive DIA microscope slides (treated water and rabbitgut) were sent to the UK Cryptosporidium Reference Unit (CRU), Swansea, Wales,for molecular typing. On 25 June 2008 a precautionary boil-water notice wasimplemented and enhanced surveillance for human disease cases was established bythe health protection team in the affected area. Enhanced surveillance was initiated on26 June. Beginning on 27 June and into July, an outbreak involving 23 cases ofcryptosporidiosis was detected in the community. The genotype found in these casesmatched that of the oocysts found in the water supply and the rabbit carcass.To reduce the potential for infection within the impacted area Anglian Water vansequipped with loudspeakers were sent out to warn people in about 108,000 homes4 Contributed by Ron Fayer, United States Department of Agriculture, and Lihua Xiao, Centres forDisease Control and Prevention, Atlanta, GA, USA.