[1] JOHNS HOPKINS UNIV, SCH HYG, DEPT MATERNAL & CHILD HLTH, BALTIMORE, MD 21218 USA
[2] JOHNS HOPKINS UNIV, SCH HYG, DEPT POPULAT DYNAM, BALTIMORE, MD 21218 USA
[3] JOHNS HOPKINS UNIV, SCH MED, DEPT PEDIAT, BALTIMORE, MD 21205 USA
[4] JOHNS HOPKINS UNIV, SCH MED, DEPT MED, DIV GEOG MED, BALTIMORE, MD 21205 USA