[1] Univ Liverpool, Liverpool Sch Trop Med, Div Trop Med, Liverpool L3 5QA, Merseyside, England
[2] Derriford Hosp, Publ Hlth Lab, Plymouth PL6 8DH, Devon, England
[3] Kidderminster Hosp, Worcestershire Acute Hosp NHS Trust, Kidderminster DY11 6RJ, England
[4] Royal Infirm, Bristol Publ Hlth Lab, Bristol BS2 8HW, Avon, England