The Texas measles outbreak that began in Gaines County has grown to 683 cases, officials said on Friday. Ten of the impacted counties in Texas have “ongoing measles transmission,” although the state public health department estimates there are currently fewer than 10 confirmed cases still infectious.

The measles outbreak centered in northwest Texas grew to 683 cases and spread to three new counties on Friday, according to health officials. The latest update from the Texas Department of State Health Services adds 20 new cases since the agency’s last update on Tuesday.

The Texas health department reported 683 cases of measles in the state on Friday, an increase of 20 since April 29, as cases of the childhood disease surpass the 900-mark in one of the worst outbreaks in the country.