[1] Inst Nacl Enfermedades Resp, Mexico City 14080, DF, Mexico
[2] Hosp Gen Gaudencio Gonzalez Garza, Ctr Med Nacl Raza, Inst Mexicano Seguro Social, Mexico City, DF, Mexico
[3] Hosp Pediat Mexico City, Unidad Invest Med Epidemiol Clin, Ctr Med Nacl Siglo 21, Inst Mexicano Seguro Social, Mexico City, DF, Mexico