I've found a bit more about the cases mentioned just below in this January 6 report in Expreso Chiapas: Se mantiene vigilancia epidemiológica en Yajalón. [Epidemiological surveillance maintained in Yajalón] Rather than translate word for word, here's a rough summary:
The state secretariat of health is running a lot of tests among the 550 people living in the small neighbourhood of Emiliano Zapata. The health brigades have visited a lot of households and checked 60 persons—55 for respiratory problems. They've taken 52 samples for lab tests, apparently to check for pertussis, though the cases they've seen aren't clinically compatible with pertussis.
The brigades have paid special attention to 41 children under 14 who are dealing with respiratory problems. Since November 14 the municipality of Yajalón has recorded five deaths of children under one year of age; two have died in week 1 of 2013. All they can say about the dead children's symptoms is "cough and unquantified fever."
A January 7 report, in Milenio.com, says the state governor is personally directing the surveillance teams and handing out 2 blankets per family, as well as donating an electrical generator.