1. Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service , Johannesburg , South Africa
2. School of Pathology, Faculty of Health Sciences, University of the Witwatersrand , Johannesburg , South Africa
3. School of Public Health, Faculty of Health Sciences, University of the Witwatersrand , Johannesburg , South Africa
4. Influenza Division, Centers for Disease Control and Prevention , Atlanta, GA , USA
5. Influenza Program, Centers for Disease Control and Prevention , Pretoria , South Africa
6. Department of Paediatrics, Mapulaneng Hospital , Mpumalanga , South Africa