Submitted on: 26 July 2004.
Revised on: 02 November 2004.
Accepted on: 14 November 2004.
___________________Acta Pediatrica de Mexico---INST NAC PEDIATRIA
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Submitted on: 21 October 2003.
Revised on: 17 January 2004.
Accepted on: 23 February 2004.
___________________Acta Pediatrica de Mexico---INST NAC PEDIATRIA
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