Henry is a 24 year old university student who presents with a 4 day history of abdominal pain and bloody diarrhoea. He has no significant past medical history. There is no history of weight loss or malaise. He noticed a rash on his lower limbs yesterday which has become a lot more pronounced overnight.
On examination his observations are unremarkable except for a temperature of 37.6 °C and you observe the below rash on the posterior aspect of both legs. Urine dipstick testing is normal.
What is the most likely diagnosis?
