[1] JOHNS HOPKINS UNIV, SCH MED, DEPT MED, BALTIMORE, MD 21205 USA
[2] JOHNS HOPKINS UNIV, SCH MED, DEPT NEUROL, BALTIMORE, MD 21205 USA
[3] UNIV PERUANA CAYETANO HEREDIA, INST NACL SALUD NINO, LIMA, PERU
[4] UNIV PERUANA CAYETANO HEREDIA, DEPT MICROBIOL, LIMA, PERU