DALLAS — Southwest Airlines is working with Dallas County health officials to identify passengers from four flights who may have been exposed to measles.

The airline confirmed an adult passenger was diagnosed with measles after flying on August 21 and August 22.

The flights were identified as:

Aug. 21: Flight #5 from Dallas Love Field to William P. Hobby Airport in Houston.

Aug. 21: Flight #9 from William P. Hobby Airport in Houston to Valley International Airport in Harlingen, Texas.

Aug. 22: Flight #665 from Valley International Airport in Harlingen, Texas to William P. Hobby Airport in Houston.

Aug. 22: Flight #44 from William P. Hobby Airport in Houston to Dallas Love Field

The measles is an acute viral respiratory illness and described by the Center for Disease Control as "one of the most contagious of all infectious diseases."

"Approximately nine out of 10 susceptible persons with close contact to a measles patient will develop measles," the CDC says. "The virus is transmitted by direct contact with infectious droplets or by airborne spread when an infected person breathes, coughs, or sneezes. Measles virus can remain infectious in the air for up to two hours after an infected person leaves an area."

Southwest Airlines issued a statement in connection to the potential measles exposure:

Our Safety & Security groups worked with the CDC to support the agency’s work in reaching our Customers who traveled onboard four intra-Texas flights last week (details below) with a passenger later diagnosed with Measles. We’ve shared awareness of the situation and protocols with our Employees who also were onboard these aircraft. Our entire fleet is subject to rigorous and regular cleaning programs and every aircraft utilizes hospital-quality HEPA filtration that improves overall quality of the air in the passenger cabin.