1. Department of Community Medicine, University of Melbourne Parkville VIC 3052
2. Department of Preventive and Social Medicine, University of Queensland, Medical School Herston Road Herston QLD 4006
3. New South Wales Health Services Research Group, Department of StatisticsUniversity of Newcastle NSW 2308
4. Virology Unit, Institute of Clinical Pathology and Medical ResearchWestmead Hospital Westmead NSW 2145
5. Mediclinics 268 Queen St Campbelltown NSW 2560
6. Department of Community MedicineUniversity of Sydney, Westmead Hospital Westmead NSW 2145