Texas’ health commissioner told lawmakers Monday they are still trying to determine the origin of a South Plains-Panhandle measles outbreak more than a month after the first patients reported symptoms.

The measles outbreak in Texas has reached nearly 150 cases, according to a Friday morning update from the state health department. The agency said 146 cases have been identified since late January. Twenty of those patients have been hospitalized, and one school-age, unvaccinated child has died.

The Mexia Independent School District reported on its Facebook page they had a confirmed case of measles, which the health department later said was not the case.