An unvaccinated New Mexico man tested positive for measles after death, becoming what health officials say could be the second death reported in the ongoing outbreak that has infected over 160 people in at least nine states.

An unvaccinated New Mexico adult who tested positive for measles has died, the second death in a growing measles outbreak centered along the West Texas-New Mexico border, officials said Thursday.

A second person with measles died, but the official cause of death hasn’t been determined.