1 Bloomsbury Institute of Intensive Care Medicine, Division of Medicine, University College London, London WC1E 6BT, UK. Electronic address: m.singer@ucl.ac.uk.
2 Department of Acute Medicine, Royal Hampshire County Hospital, Hampshire Hospitals NHS Foundation Trust, Winchester, UK; NHS England, London, UK.
3 Institute of Child Health, University College London, London, UK; Paediatric Intensive Care Unit, Great Ormond Street Hospital for Children, London, UK.
4 Department of Paediatric Infectious Disease, Faculty of Medicine, Imperial College London, London, UK; Kenya Medical Research Institute/Wellcome Trust Research Programme, Kilifi, Kenya.