Cryptosporidium in drinking water and dental unit waterlines

Mini-review by: Stine Skotte Bjerregaard, Adept Water Technologies, May 2014. Contact

Cryptosporidium is a common intestinal protozoan of animals, and a human parasite, which can be waterborne as an oocyst [1][2]. Cryptosporidium can cause symptoms such as mild to severe diarrhea, fever and headache. The symptoms can in some cases last for 2-3 years, and for immunocompromised people, Cryptosporidium can cause chronic gastroenteritis [3]. Outbreaks of Cryptosporidium in municipal water have happened in several countries; The United Kingdom, France, Australia, Sweden and USA. In Sweden about 20,000 people became ill from Cryptosporidium infection, and in Milwaukee, USA more than 403,000 people became ill from Cryptosporidium infection, which even caused mortality in several cases [3][4].

Cryptosporidium has been detected in water from dental unit waterlines (DUWLs), and a study in Alexandria, Egypt showed that 27.5% of dental unit irrigation machines were contaminated with Cryptosporidium species [4]. In waterlines for municipal drinking water, Cryptosporidium oocysts can survive from weeks to 2-3 months, but in DUWLs Cryptosporidium can survive for even longer periods in bacterial biofilm, which can become a reservoir for Cryptosporidium [3]. Furthermore the Cryptosporidium oocysts are close to impossible to inactivate with various disinfectants, hence it is of outmost importance to prevent Cryptosporidium from entering the DUWLs [3][5].

Reverse osmosis or absolute 1 micron filters (or smaller pore size) can prevent Cryptosporidium in municipal water from entering the DUWLs, however if using a filter, an immunocompromised person should not change the filter, due to infection risk of concentrated numbers of Cryptosporidium in the filter [6]. It can be advantageous to trap

Cryptosporidium in a filter with <1 micron pore size, and persistently treat it with a disinfectant, which over time will kill the Cryptosporidium oocysts and make it safe to change the filter.


  • Zhilin R and Shaofeng L. Inactivation of Cryptosporidium and Giardia by chlorine in water. Advanced Materials Research Vols. 726-731 2013 pp. 392-395
  • World Health Organization (WHO). Risk assessment of Cryptosporidium in drinking water 2009.
  • Claesson R, Bäckman N, Edwardsson S, and Johansson A. Patogener I unitens vatten. Tandläkartidningen 2013 105:9 pp. 62-67.
  • Mac Kenzie W R, Hoxie N J, Proctor M E, Gradus S, Blair K A, Peterson D E, Kazmierczak S G, Addis D G, Fox K R, Rose J B, and Davis J P. A massive outbreak in Milwaukee of Cryptosporidium infection transmitted through the public water supply. The New England Journal of Medicine 1994 vol. 331 no. 3 pp. 161-167
  • Hassan A, Farouk H, Abdul-Ghani R, and Hassanein F. Contamination of irrigation systems of dental units with Cryptosporidium species in Alexandria, Egypt: a neglected disinfection pitfall. Risk Management and Healthcare Policy 2012 Issue 5 pp. 93-95
[5] Center of Disease Control (CDC)