David M Murdoch1,3,5
, Willem DF Venter2
, Annelies Van Rie3
and Charles Feldman4 
1Division of Pulmonary and Critical Care Medicine, Duke University Medical Center, Durham North Carolina, USA
2Reproductive Health & HIV Research Unit, University of the Witwatersrand, Johannesburg, South Africa
3Department of Epidemiology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
4Division of Pulmonology, Department of Medicine, Johannesburg Hospital and University of the Witwatersrand, Johannesburg, South Africa
5CB#7435, 2104-H McGavran-Greenberg Hall, University of North Carolina, School of Public Health, Chapel Hill, NC 27599-7435, USA