Texas and New Mexico on Tuesday reported an increase of 28 cases of measles in the last five days, bringing the total known infections to 256 in the two states since an outbreak began in late January.

A measles outbreak that began in northwest Texas grew to 223 cases on Tuesday, with another 33 cases reported in New Mexico, according to health officials. Update 5:30 p.m. March 11: This story has been updated to reflect that New Mexico health officials announced three new measles cases on Tuesday,

The outbreak has sickened nearly 200 people in Gaines County, Texas. A neighboring county in New Mexico has seen 21 new cases since Tuesday.