Dr Warren is one of the first doctors to be trained in both infectious diseases and microbiology and he provides services across both departments. He is particularly interested in chronic infections, such as diabetic foot infection and vascular graft infection and is involved in the provision of the out-patient antibiotic service.

His main area of expertise is bone and joint infection and he provides the infection service for the Royal National Orthopaedic Hospital where he works closely with the surgical consultants. He sees complex cases, many of which are tertiary referrals from all over the country, who have typically had problems for many years before being referred for a further opinion.