[1] CTR DIS CONTROL, CTR INFECT DIS, DIV VIRAL & RICKETTSIAL DIS, ATLANTA, GA 30333 USA
[2] EMORY UNIV, SCH MED, DEPT PEDIAT, ATLANTA, GA 30322 USA
[3] UNIV MASSACHUSETTS, SCH MED, DIV INFECT DIS, WORCESTER, MA 01605 USA
[4] JOHNS HOPKINS UNIV, SCH HYG & PUBL HLTH, DEPT INT HLTH, BALTIMORE, MD 21218 USA