There have been several outbreaks of protozoal infections from water in several countries. For instance, each year in the UK there are 3000–6000 confirmed cases of cryptosporidiosis, caused by the protozoa Cryptosporidium; the largest outbreak was in Torbay, Devon in 1995, when 575 people were taken ill (Hunter et al., 2003).
The most common symptom of cryptosporidiosis is watery diarrhoea. Other symptoms include stomach pain, nausea, vomiting, fever and weight loss (Centers for Disease Control and Prevention, 2010). In addition, some people can act as carriers of Cryptosporidium.
Another, similar condition is giardiasis, caused by the protozoa Giardia. Giardiasis outbreaks are not common in the UK, but one occurred in Bristol in 1985, when 108 cases were diagnosed (Jephcott et al., 1986).
Techniques for sampling and analysis of Cryptosporidium are complicated and time-consuming, requiring the filtration of large volumes of water (100–1000 litres), followed by several stages of elution, isolation and concentration of the oocysts, and then identification and enumeration by immunofluorescent microscopy. Initial testing does not provide information on whether the oocysts are viable and therefore capable of causing disease – this requires further testing. As a result, there is no specific standard for the organism in EU or UK regulations. There is, however, a general requirement that drinking water should not contain any microorganism or parasite at a concentration that would constitute a potential danger to human health (Water UK, 2011).
Cryptosporidium and Giardia can be trapped by membrane filtration or slow sand filters. Other types of filters, such as wound fibre filters, are also employed. Chlorination and UV radiation at normal doses are ineffective against these organisms.