More evidence than ever that Cryptosporidium infection has long term impacts on health

04 July 2022


Cryptosporidiosisis a disease caused by infection of a host by the parasite Cryptosporidium, usually C. hominis or C. parvum, and is often associated with contaminated food or farm animal contact. Whilst diarrhoea is a common symptom of infection in the acute phase, longer-term health risks to the majority of the population in industrialised countries are considered low. However, increasing volumes of evidence suggest that long-term impacts of infection are still present up to 28 months after infection, potentially seriously affecting patients’ quality of life – an understanding which researchers hope will be reflected in public health measures in the future.

The team at the Public Health Wales Cryptosporidium Reference Unit and Swansea University Medical School, UK has been gathering evidence for some time about the long-term effects of infection and is concerned about the lack of awareness. Team member Professor Angharad Davies says “Although people have given some consideration to the long-term impact of infection in developing countries, in industrialised countries that’s not really been on the agenda until recently… people haven’t realised the impact of infection long-term, or the burden on families after the acute symptoms have passed.”

Gathering evidence from their research studies and their systematic review of the literature, the team has raised awareness of these long-term impacts. A wide range of symptoms have been identified by the team. These included symptoms associated with Irritable Bowel Syndrome (IBS) such as abdominal pain, long-term diarrhoea and weight loss, in addition to a wider range of symptoms including fatigue and joint pain.

Through their systematic review, the research team found that after infection by C. hominis, patients were at six times higher risk of reporting chronic diarrhoea and weight loss after 28 months, compared with controls. A cohort follow-up study following an outbreak in northern England, believed to have bagged salad as the source, had similar findings, with 38% of patients reporting abdominal pain, 33% diarrhoea, 33% joint pain and 31% weight loss at 12 months. Prof. Davies is quick to highlight the limitations of this study: “These symptoms were being self-reported and were subject to recall bias, especially for any symptoms present prior to the infective episode, since by the time the outbreak had been reported and patients identified we couldn’t collect the information prospectively.”

This work led to a prospective study of patients in Wales who had a laboratory diagnosis of Cryptosporidium infection, with the aim of establishing whether IBS could be a longer-term outcome of Cryptosporidium infection. By contacting all patients over six months of age with a diagnosis over the course of two years, the team found that 10% of patients had since received a formal IBS diagnosis, whilst another 50% fulfilled many of the criteria required for a diagnosis, with the risk even higher in children, something that had not previously been recognised.

Prof. Davies hopes that this finding will encourage public health officials to recognise the full range of risks of infection: “Although previous work had suggested children rarely develop sequelae, a lot of children had symptoms relating to IBS once you asked the right questions… My hope is that knowing the long-term impacts of Cryptosporidium infection will encourage authorities to further prioritise prevention of this infection. Many outbreaks can be prevented by public health measures and there is still more that can be done to prevent infections from happening.”

Prof. Davies will present her work at the Microbiology Society’s ‘What’s New in Cryptosporidium?’ Focused Meeting on 5 July at 09:40 BST.

Image: Dr Guy Robinson.