The perfect storm for another U.S. measles outbreak may include a busy international airport.

Researchers at the University of Texas at Austin and Johns Hopkins University have identified 25 U.S. counties that are most at risk for a measles outbreak. The paper was published earlier this month in The Lancet Infectious Diseases.

They found that the U.S. county most at risk was Cook County in Illinois, which is also home to O’Hare International Airport in Chicago, the country’s busiest airport.

Los Angeles, Miami-Dade, Queens, N.Y. and King in Washington State round out the top five counties the group predicted to be at greater risk for the vaccine-preventable disease. All have numerous daily international flights at airports contained in their boundaries.

Other counties that were identified at a lower risk include Philadelphia, ranked 29th, and Allegheny County — which is where all five of Pennsylvania’s 2019 cases have been reported — ranked 31st. Essex County in New Jersey was ranked 15th, according to the study.

The cases in Pennsylvania all have ties to international travel.

As of May 6, the Allegheny Department of Health has reported five cases of measles. The first reported case in April was a non-vaccinated individual who had traveled internationally. The other four cases come from one family where three of members were visiting from overseas. The other family member is a Pennsylvania resident who was not vaccinated.

Map reveals the number of WHO reported measles cases around the world since 2018;
p.holm / AP
Map reveals the number of WHO reported measles cases around the world since 2018;

There were four counties in Florida and three in each of California and Texas that made the list. Currently 18 states, including Pennsylvania, allow nonmedical exemptions for vaccinations.

So far this year, there have been 839 reported cases of measles as of May 10, according to the Centers for Disease Control and Prevention.

“We are set to see over 1,000 cases in the U.S. in 2019,” said lead author, Sahotra Sarkar, a philosophy and integrative biology professor at UT Austin. For the first time since the 1980s, there may be U.S. infant deaths from measles, he said.

The researchers looked at four factors they determined would compound the risk for a measles outbreak. They found that the number of international flights into the county, the incidence rate of measles at the flight’s country of origin, the nonmedical vaccination exemption rates in the U.S. destination and population of the counties played a significant role in the spread of the highly contagious virus.

Using the risk analysis they developed, the researchers have already successfully predicted outbreaks in Washington State, Oregon and New York, according to the study paper.

The countries that appear to pose the greatest risk for travelers include India, China, Mexico, Japan, Ukraine, the Philippines and Thailand, where there are already outbreaks of measles, researchers found.

There have already been reported cases of measles that were traced back to nations including Ukraine, the Philippines and Thailand.

Researchers said the risk analysis should be applied to other vaccine-preventable illnesses such as mumps, rubella, and pertussis.

“The vaccine avoidance problem is not limited to measles," Sarkar said. Pertussis, or whooping cough, is making a comeback because of dropping vaccination rates, he said.

Symptoms of the measles include fever, cough, runny nose, red-watery eyes and the telltale red spotted rash. While most of those who are infected recover, some go on to develop pneumonia and brain swelling. There are about one or two deaths per 1,000 people affected, according to experts.

The disease was declared officially eliminated in the U.S. in 2000.