At least two passengers on an international flight that arrived in San Francisco in February contracted measles from an infected person who was on the same flight, the city’s department of public health said in a statement Wednesday.

Public health officials did not disclose the infected person’s flight number or what airline they were using. It's unclear where the San Francisco-bound flight took off from.

The two passengers — who the San Francisco Department of Public Health did not identify but noted live in San Francisco and Santa Clara County, respectively — were exposed to the viral infection from a third passenger, a resident of Santa Cruz County, who likely contracted measles while abroad.

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It’s not known if the passenger who was initially infected was aware he or she had contracted measles ahead of the flight.

“The general public is at very low risk of measles as a result of these cases,” the San Francisco Department of Public Health said, noting no other passengers on the flight have contracted the disease.

“The flight was more than three weeks ago. Measles develops within 21 days of exposure. Public health investigators have not identified any evidence indicating that measles is spreading within the impacted counties,” health officials said.

"The general public is at very low risk of measles as a result of these cases." — San Francisco Department of Public Health

Measles is a highly contagious viral infection that is spread in the air when an infected person coughs or sneezes. People can also contract measles if they come into contact with the mucus or saliva of an infected person. Though symptoms sometimes do not appear for weeks, typical signs of measles include a high fever, rash, cough and red, watery eyes.

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Common complications include ear infections and diarrhea, but more severe complications — such as pneumonia, encephalitis (swelling of the brain) — can also occur, according to the Centers for Disease Control and Prevention (CDC).

So far this year, the CDC has confirmed individual cases of measles in 11 states. In Washington state alone, there have been 71 confirmed cases, the state's department of health said in a March 4 update.

“Making sure you have all your immunizations is especially important for travelers because measles is circulating in many countries outside the United States,” the San Francisco Department of Public Health added, recommending infants between six and 11 months of age receive a measles vaccine before embarking on an international trip.