A person who boarded a train to Chicago in Missouri late last month has tested positive for measles, becoming the first confirmed case in a St. Louis County resident in 20 years, health officials announced Thursday.
The person boarded a Chicago-bound train Aug. 27 that also carried another person who boarded the Missouri River Runner (Train 318) in Sedalia and was later confirmed to have measles. Jackson County health officials confirmed that initial case earlier this week.
Both people were vaccinated against the disease, which is extremely contagious, said Jesse Hackell, a pediatrician who has written several reports on vaccine policy for the American Academy of Pediatrics. While the vaccine is highly effective, around 3% of people who receive it don't mount an immune response.
"So if you're talking about a train with 100 people on it, there are going to be three susceptible people there," he said. "It's perfectly consistent with everything we know about how effective the measles vaccine is."
In total, four people who rode the train tested positive for measles, county representatives confirmed. They did not say where the other two infected people were from or where they were going.
Officials with the St. Louis County Department of Public Health said they are investigating the case and working with state and local officials to identify others who may have been exposed.
"Measles is one of the most contagious diseases we see, which is why identifying potential exposures quickly is so important, as is abiding by isolation and quarantine requests by the health department," county Health Director Dr. Kanika Cunningham said in a press release announcing the case.
Health authorities did not offer much information about the St. Louis County patient. He lives in north St. Louis county and has been recovering well, Cunningham said. The man works as a teacher and has transitioned to virtual classes to keep himself isolated.
It's possible more people could have been infected on the train, Hackell said, because of the close quarters, the amount of time it takes for the train to travel from one city to another and how contagious measles is. The virus travels through the air and is expelled when an infected person coughs, breathes or sneezes.
Although it's most common for symptoms to show up within one or two weeks, some people can start exhibiting symptoms three weeks after exposure.
"We know if we have a patient in our office with measles, that exam room is off limits for at least two hours, [because] we know that the virus can live in the air of a room for at least two hours," Hackell said. "If you had people who were in and out of the train, they should be looking for 21 days from the day of the exposure to think that they're sort of out of the woods."
Measles symptoms typically start one to two weeks after a person is exposed but can show up as late as three weeks later. The virus travels through the air and is expelled when an infected person coughs, breathes or sneezes.
Symptoms include cough, fever, red eyes and a runny nose, as well as the trademark measles rash. Sometimes, white spots appear inside a patient's mouth after the onset of symptoms.
Measles can cause severe illness or death, particularly in young children and babies. According to the Centers for Disease Control and Prevention, approximately 1 to 3 of every 1,000 people with measles die from the disease. Approximately 1 in 5 unvaccinated people who get measles end up in the hospital.
Still, Cunningham said the overall risk for the region is still minimal.
"If you have not received a phone call from our department at this point, you know your risk is still low," she said. "We're working directly with those individuals that we have identified with being exposed. But as far as a regional exposure is concerned, that risk is super super low right now, so no reason to panic or become alarmed."
Measles rates have risen nationwide as fewer people opt to get themselves and their children vaccinated. Four people have died in Pennsylvania this year during a measles outbreak in the state.
Missouri has reported seven measles cases so far this year.
If a population's vaccination rate falls below 95%, the risk of an outbreak increases. Vaccination rates have dropped over the past five years in Missouri, with fewer than 90% of kindergarten students receiving the two-shot MMR vaccine.
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