We agree with Viget et al (Gut 2008;57:549–58) with regard to the importance of preventing and diagnosing opportunistic pathogens in patients with inflammatory bowel disease who are receiving immunomodulatory drugs. We would like to point out another important pathogen worthy of mention, its treatment and prevention by illustration with a 20-year-old woman with Crohn’s disease recently treated in our unit. She presented with a 7-day history of worsening diarrhoea, occurring up to 15 occasions per day. Her Crohn’s disease was well controlled on azathioprine 125 mg daily. She was apyrexial, dehydrated and tachycardic. Abdominal examination revealed tenderness on deep palpation of the umbilical region but no guarding.

Blood tests revealed a neutrophil leucocytosis but abdominal x ray was unremarkable. Microscopy of a stool sample obtained revealed cysts of Cryptosporidium spp. confirmed as Cryptosporidium parvum by polymerase chain reaction. No other organisms were isolated and culture …