1. Department of Mathematics and Statistics University of Otago Dunedin New Zealand
2. Centre for International Health University of Otago Dunedin New Zealand
3. Department of Medicine University of Otago Christchurch New Zealand
4. Department of Preventive and Social Medicine University of Otago Dunedin New Zealand
5. Division of Infectious Diseases Duke University Durham North Carolina USA
6. Bacterial Special Pathogens Branch US Center for Disease Control and Prevention Atlanta Georgia USA