aDivision of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, USA
bJohns Hopkins University School of Medicine, USA
cJohns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
dMakerere University School of Public Health, Kampala, Uganda.
Received 9 April, 2009
Accepted 9 April, 2009