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Garza-Ramos U, Silva-Sánchez J, Martínez-Romero E.Garza-Ramos U, et al.Salud Publica Mex. 2009;51 Suppl 3:S439-46. doi: 10.1590/s0036-36342009000900009.Salud Publica Mex. 2009.PMID: 20464217Review.Spanish.