The measles outbreak that began in West Texas is still growing, with exposures on university campuses and other places in San Antonio and San Marcos.

A Texas measles outbreak has doubled in the last week to 124 cases, state health officials said Tuesday, a day after they warned a person infected with the highly contagious disease had traveled from the outbreak zone.

Texas is in the midst of the worst measles outbreak in decades, with 90 cases across 7 counties. Here’s what to know.