Cryptosporidium is a protozoan parasite that has emerged as an important cause of diarrhoeal illness worldwide, particularly in young children and immunocompromised patients. In the UK Cryptosporidium is the commonest protozoal cause of acute gastroenteritis, with 3000-6000 laboratory confirmed cases annually, although this is almost certainly an underestimation of the disease burden. Two species, Cryptosporidium hominis and Cryptosporidium parvum, account for most of these laboratory-confirmed cases. Species distinction between C hominis and C parvum is quite recent and for several years both parasites were referred to as C parvum (sometimes genotypes 1 and 2). Large waterborne outbreaks highlight the parasite’s clinical and economic importance.

The clinical problems associated with Cryptosporidium are increasingly becoming recognised internationally, and the parasite was included in the World Health Organization’s Neglected Diseases Initiative 2004. These neglected diseases are defined as those that “exhibit a considerable and increasing global burden, and impair the ability of those infected to achieve their full potential, both developmentally and socio-economically”.1

In this review, we assess the epidemiology, clinical presentation, diagnosis, and management of cryptosporidiosis, and consider its epidemiology.