1. Centre for Applied Microbiology and Research, Salisbury SP4 0JG
2. Meningococcal Reference Unit, Manchester Public Health Laboratory, Withington Hospital, Manchester M20 2LR
3. National Institute for Biological Standards and Control, South Mimms, Potters Bar EN6 3QG
4. Public Health Laboratory, Gloucestershire Royal Hospital, Gloucester GL1 3NN, United Kingdom