title: Approaches to the detection of very small, common, and easily missed outbreaks that together contribute substantially to human Cryptosporidium infection.
abstract: Water supply-associated cryptosporidiosis outbreaks have decreased in England since the application of risk reduction measures to public water supplies. We hypothesized that smaller outbreaks were occurring which could be better detected by enhanced surveillance. Rolling analysis of detailed questionnaire data was applied prospectively in a population of 2·2 million in the south of England in 2009 and 2010. Detection of spatiotemporal clusters using SaTScan was later undertaken retrospectively. Together these approaches identified eight outbreaks, compared to an expectation of less than one based on national surveillance data. These outbreaks were small and associated with swimming pool use or, less commonly, direct (e.g. petting-farm) contact with animals. These findings suggest that frequent small-scale transmission in swimming pools is an important contributor to disease burden. Identification of swimming pool-level risk factors may inform preventative measures. These findings and the approaches described may be applicable to many other populations and to some other diseases.
authors.affiliation: Thames Valley Public Health England Centre, Chilton,UK.
authors.forename: A D M
authors.initials: AD
authors.lastname: Briggs
authors.affiliation: Field Epidemiology Service,Public Health England,London,UK.
authors.forename: N S
authors.initials: NS
authors.lastname: Boxall
authors.affiliation: Thames Valley Public Health England Centre, Chilton,UK.
authors.forename: D
authors.initials: D
authors.lastname: Van Santen
authors.affiliation: UK Cryptosporidium Reference Unit,Public Health Wales Microbiology,Swansea,UK.
authors.forename: R M
authors.initials: RM
authors.lastname: Chalmers
authors.affiliation: Thames Valley Public Health England Centre, Chilton,UK.
authors.forename: N D
authors.initials: ND
authors.lastname: McCarthy
mesh_terms: D003457:Cryptosporidiosis / Q000175:diagnosis* / Q000453:epidemiology*; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D004739:England / Q000453:epidemiology; D006801:Humans; D008954:Models, Biological; D009010:Monte Carlo Method; D014881:Water Supply