[1] IMSS, Med High Special Unit, Canc Populat Record Merida, Merida, Yucatan, Mexico
[2] Star Med Hosp, Merida, Yucatan, Mexico
[3] IMSS, Dept Clin Neonatol, Reg Hosp 1, Merida, Yucatan, Mexico
[4] IMSS, Gen Hosp 1, Zacatecas City, Zacatecas, Mexico
[5] Autonomous Univ Yucatan, Clin & Epidemiol Interinst Res Unit, Fac Med, Merida, Yucatan, Mexico
[6] Natl Inst Resp Dis INER, Allergy & Immunogenet Dept, Mexico City 14080, DF, Mexico