1. Experimental Bacteriology; National Institute of Pediatrics; SSA; México D.F. México
2. Gastroenterology & Nutrition Department; Children's Hospital of Mexico “Federico Gómez”; SSA; México D.F. México
3. Infectious Diseases Research Unit; Instituto Mexicano del Seguro Social; Mexico City Mexico, CMN Siglo XXI, IMSS, México, D.F., México
4. Infectology Laboratory; Children's Hospital of México “Federico Gómez”; SSA; México D.F. México
5. International Maize and Wheat Improvement Center; Biometrics and Statistics Unit; Mexico Mexico