Two Texas universities and their surrounding communities have issued warnings about potential exposure to measles after giving campus tours to at least one person who tested positive for the virus. Experts have been tracking the measles outbreak in Gaines County since late January.

Confirmed measles cases in Texas have reached at least 90, making this the worst measles outbreak in 30 years. Experts warn the number of Texas cases is likely much higher.

Texas reported 90 cases this week, while New Mexico reported nine. A majority of the cases have been in a Texas county where vaccination rates have lagged behind the rest of the state.