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.

The largest measles outbreak in decades has reached San Antonio and San Marcos. Officials say an individual who tested positive for the virus in West Texas traveled to two major universities and one of the nation's busiest tourist attractions — the San Antonio River Walk.