Clinical Review


BMJ 2009; 339 doi: (Published 19 October 2009) Cite this as: BMJ 2009;339:b4168

This article has a correction. Please see:

  1. A P Davies, clinical senior lecturer/honorary consultant microbiologist1,
  2. R M Chalmers, consultant clinical scientist and head of unit2
  1. 1School of Medicine, Swansea University, Swansea SA2 8PP
  2. 2UK Cryptosporidium Reference Unit, National Public Health Service for Wales, Swansea
  1. Correspondence to: A P Davies angharad.p.davies{at}
  • Accepted 4 September 2009

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.

Sources and selection criteria

We searched MEDLINE for authoritative articles and studies and by consulting the archived resources of the UK Cryptosporidium Reference Unit, Swansea, of which one of the authors (RMC) is the head. The Cochrane database contains a systematic review of treatment in the immunocompromised.2

Who gets cryptosporidiosis?

Anyone can be infected and become ill with Cryptosporidium. Cryptosporidiosis is commoner in young children, particularly in those under age 5 years, but the disease can also affect healthy people of any age. However, most clinical problems are encountered in patients who are profoundly immunocompromised. Asymptomatic carriage of the organism is possible: a recent study of young children in day care nurseries found that three of 230 (1.3%, upper 95% CI 3.8%) were carrying the parasite …

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