Cryptosporidium: What is the water parasite and how dangerous is it?

Cryptosporidiosis can affect 3,000-6,000 people a year across the UK, according to the latest available data, external.

Prof Hunter, who sits on a World Health Organization committee on drinking water quality, says outbreaks are less common these days after new laws were brought in forcing UK water companies to do more testing for cryptosporidium.

However, he says data on outbreaks is no longer regularly published.

“It is often difficult to know how many outbreaks we are seeing,” he says.

“Drinking water isn’t the only cause of outbreaks, we see outbreaks in swimming pools quite often, there have been outbreaks associated with drinking unpasteurised milk, and we see outbreaks in nurseries.”