The Texas health department reported 663 cases of measles in the state on Tuesday, an increase of 17 cases since April 25, as the U.S. battles one of its worst outbreaks of the childhood disease. Cases in Gaines County,

The number of cases reported in Texas' historic measles outbreak has risen to 663 cases in 26 counties, as of April 29. Of those, 87 patients have been hospitalized, and two school-aged children have died since the outbreak began in January.

As more counties are being impacted by the ongoing measles outbreak and added to the growing list of counties across Texas, here's what to know.