SARS, Ebola and covid highlighted role of plane travel in spreading — and tracking — outbreaks.

“Basically, the pilot took one look at this sweating patient and said, ‘you look like hell, and you’re out of here,’” recalled Freedman, a professor emeritus at the University of Alabama at Birmingham, who helped create a global network for tracking infectious diseases among travelers.

That no-fuss decision is an example of how U.S. authorities rely on airlines as one layer of the informal front lines in detecting and curtailing infectious-disease — a long-standing effort that has been expanded and beefed up following successive worldwide outbreaks of SARS, Ebola and covid-19.

Now, with the world on edge after a lab technician’s death potentially linked to pneumonic plague in Russia, this system could be put to the test again.

Russian authorities have been tight-lipped about what exactly happened with the worker at the Irkutsk Antiplague Research Institute of Siberia and the Far East. But in a post-covid world, the idea that a remote case of a rare disease could spiral into a worldwide catastrophe no longer seems far-fetched.

The role of airlines in disease surveillance and containment systems comes with an imperfect track record. But the potential capability of these intricate worldwide networks to not only spread diseases but also act as an early-warning system against them is viewed with growing importance.

“Compared to where we used to be, we’re way further ahead in terms of those rare events that are harbingers of a big outbreak event,” Freedman said.

Flight crews are not expected to diagnose diseases, but they may conduct what’s known as passive surveillance of passengers for signs of illness. There are also projects to test airplane wastewater for emerging threats and plans for air sampling in major international airport hubs. In the U.S., authorities have not been shy about using powers to limit or reject entry of people into the country based on health status and the potential for disease outbreaks.

In April, U.S. authorities issued a 42-day quarantine for 18 American passengers who’d been on a Dutch cruise ship that was hit by a deadly outbreak of Andes hantavirus while at sea. That length of isolation, which some passengers completed at the University of Nebraska Medical Center, went well beyond post-exposure guidelines for most contagious diseases.

A month later, the Trump administration stopped foreigners and certain noncitizens from entering the U.S. if they’d recently been to the Democratic Republic of Congo, which was in the grip of an Ebola outbreak.

Two months after that, the administration took the unusual step of barring American citizens returning from Congo on flights until they’d first spent 21 days in a third country. These are so-called “Do Not Board” orders.

Also, certain American citizens and U.S. nationals traveling from Uganda or South Sudan within 21 days were required to fly to U.S. airports equipped with public health entry screening. Twenty-one days is the maximum incubation period for Ebola, a highly lethal deadly hemorrhagic fever. The travel limits remain in effect, with renewals every 30 days.

There are no direct flights from Russia to the U.S. due to sanctions and the suspension of service following Russia’s 2022 invasion of Ukraine. But travelers can legally fly through Istanbul and other hubs. If Russia’s one potential plague death becomes a more extensive outbreak, the U.S. could possibly respond by deciding to implement “Do Not Board” orders for people who have been to certain parts of Russia recently, Freedman said.

In public health terms, a potential upside with most plague infections is that asymptomatic spread is rare.

“Plague is not contagious until somebody is very, very sick and obviously sick,” Freedman said.

Since the coronavirus pandemic, the Centers for Disease Control and Prevention (CDC) has expanded efforts to test plane wastewater. The CDC began with a 2022 pilot project at John F. Kennedy International Airport in New York, sampling some international flights. The program has been extended to a handful of other domestic airports. But these systems are not yet designed to screen for plague.

A team from Qantas Airlines and the University of Queensland has proposed a worldwide genomic surveillance system using aircraft wastewater “for early warning of future pandemics.”They even invented a tool to more easily trap samples without clogging up the pipes or using the old method of “a bucket under the waste tanker.”Wastewater testing “will tell you something, but it may be too late. If they flew from Kazakhstan to Atlanta and then to Austin — by the time they figure it out, who knows where you are?” she said. The precautions could make us safer, she said, but there is still a risk.

“The airlines are doing a great job cleaning the cabins and filtering the air and watching for signs of trouble,” Hertzberg said. “But if you’re sitting next to someone on a long flight and they have something, you’re still in big trouble.”