OKMULGEE COUNTY, Okla. – Health officials in Okmulgee County say three additional cases of measles have been identified in the state.

Earlier this month, the Oklahoma State Department of Health announced that the first measles case was confirmed in the Sooner State in Tulsa.

Now, officials say the number of confirmed measles cases in Oklahoma has grown to four.

Investigators say all three other cases are close contacts of the initial patient, and no other cases of measles have been identified in any counties outside of Okmulgee County.

Health officials say they are still investigating, and have interviewed more than 250 people that might have come into contact with the virus.

“This is a coordinated effort by a number of public health professionals,” said State Epidemiologist Laurence Burnsed. “It is important for us to identify settings where individuals may have been exposed to advise them of their risk and implement measures to prevent the spread of illness to those who may be unvaccinated, and persons who may be at greater risk of illness due to compromised immune systems or children who may not be old enough to receive full protection.”

As of May 24, there have been 940 cases of measles in 26 states across the country, making it the highest number of cases in the U.S. since 1994.

A person can spread the illness four days before and four days after developing the rash and therefore may unknowingly spread it. The virus can be airborne for up to two hours and spreads when an infected person coughs or sneezes.

“Measles is so contagious that if one person has it, up to 90% of the people close to that person who are not immune will also become infected,” according to the CDC.

Symptoms of measles begin with a mild to moderate fever, runny nose, red eyes, and cough. A few days later, a rash appears starting on the face spreading to the rest of the body accompanied by a fever that can reach up to 105 degrees. Measles can lead to pneumonia and other complications, especially in young children and adults over 20 years of age. The disease can also cause serious problems in pregnant women and those with weakened immune systems.

Individuals are protected if they are immunized with two doses of a measles-containing vaccine after their first birthday, or if they were born during or before 1957, or if they have previously had the measles.

Approximately 90 percent of U.S. cases reported so far this year were either unvaccinated or had an unknown history of vaccination against measles.

Anyone who is concerned about possible exposure should contact public health officials at 800-234-5963.