Tarrant County health officials say Wednesday that 15 people have been confirmed to have contracted measles and that 11 of those people had not been immunized.
Twelve of the infected have recovered from the illness. Those who are still infectious have been asked to remain at home.
Health officials said there may be several other cases of measles under investigation that have not been confirmed and have not been added to the official tally.
The cases include both children and adults who range in age from 4-months-old to 44-years-old. All of the infected children are home-schooled.
Earlier Wednesday, health officials in Denton County confirmed they have five cases of measles in children ranging in age between 9-years-old and 17-years-old. None of the children were immunized , all live in the Justin area and the cases are believed to be related to the Tarrant County cases.
Denton County also had two cases of measles earlier this year; those cases are not believed to be connected to the most recent outbreak.
Officials said Tuesday morning that a North Texas church, the Eagle Mountain International Church in Newark, may be at the center of the outbreak.
Dr. Karen Smith confirmed the first measles case was from a person that visited the congregation a few weeks ago after returning from a trip to Asia. As of Monday, the church confirmed nine cases of measles were within their congregation.
According to the Centers for Disease Control and Prevention, "measles is a respiratory disease caused by a virus. The disease of measles and the virus that causes it share the same name. The disease is also called rubeola. Measles virus normally grows in the cells that line the back of the throat and lungs."
People with symptoms of measles have a fever, runny nose, cough and a rash all over the body. The incubation period of measles is about two weeks from exposure to the onset of a rash, the Texas Department of State Health Services said. People are contagious from four days before the onset of a rash to four days after the appearance of rash. The rash usually begins on the face and spreads to the trunk.
It is spread through the air by breathing, coughing or sneezing and is so highly contagious that any child who is not immune and is exposed to the virus should expect to contract the virus. With that in mind, health officials are urging those who are susceptible to the disease to get immunized.
NBC 5's Eric King contributed to this report.