US health officials have quarantined a man who may have exposed passengers on board two trans-Atlantic flights to a dangerous form of tuberculosis.
Tuberculosis is a bacterial infection spread through the air
Officials say crew and passengers on the same flights, from Atlanta to Paris and from Prague to Montreal this month, should be checked for the infection.
The Centers for Disease Control and Prevention has identified the illness as "extensively drug-resistant TB".
It is the first such federal quarantine order to be issued in over 44 years.
The last such order was issued in 1963, to quarantine a patient with smallpox, according to the CDC.
Tuberculosis is a bacterial infection that usually attacks the lungs. It is spread through the air and can lead to symptoms such as chest pain and coughing up blood.
There were an estimated 1.6 million deaths from TB in 2005, according to the World Health Organization (WHO).
The infected man travelled from Atlanta to Paris on 12 May on Air France flight 385. He returned to the North America on CSA flight 104 from Prague to Montreal on 24 May.
He continued his journey in the US by car and is now under quarantine in hospital, according to the WHO.
CDC officials said the man was potentially infectious during this period and are recommending that crew members and passengers on board the same flights seek medical attention.
"We want to make sure that we have done everything we possibly can to identify people who could be at risk," said Dr Julie Gerberding, director of the CDC.
TB is rare in the US. Last year there were 13,767 recorded cases or 4.6 cases per 100,000 Americans.
About 1.2% of cases in the US are "multidrug-resistant", and can withstand antibiotics commonly used to treat the illness, according to CDC statistics.
The "extensively drug-resistant" TB is more dangerous. Medical treatment can cost $500,000 (£250,000) or more, CDC officials say.