Measles is a respiratory virus that can survive in the air for up to two hours. Up to 9 out of 10 people who are susceptible will get the virus if exposed, according to the U.S. Centers for Disease Control and Prevention.

A measles outbreak in rural West Texas, rising to 58 cases as of Tuesday (February 18), has spread to neighboring New Mexico. Eight people in eastern New Mexico have now contracted the highly contagious infection though a spokesperson for the state's health department says it hadn't “identified any direct contact” in cross-state cases.

The measles outbreak in Texas has escalated sharply to 90 cases as health officials worry about the spread to more communities.