Six young children at a Texas day care center have tested positive for measles — a dreaded scenario with the potential to accelerate an already out-of-control outbreak.

The measles outbreak in western Texas has hit 481 cases as 59 newly identified infections were confirmed over the last three days, according to new data published Friday.

The measles outbreak that began in northwest Texas has now surpassed a combined 500 cases in Texas, New Mexico and Oklahoma.