Measles is spreading fast among workers at Kansai International Airport, with 32 airport workers in their 20s and 30s found to have contracted the viral disease since mid-August, officials said.

In addition to the 32, three other medical workers who dealt with measles patients were confirmed Sunday to have been infected.

Kansai Airports, the company that operates the major airport in the southern part of Osaka Prefecture, said Monday that 25 of those who contracted the disease are recovering.

Nonetheless, the operator is stepping up vigilance as measles is highly contagious and some of the workers are believed not to be vaccinated against it.

“The outbreak seems to have passed its peak, but if someone who was exposed at the end of August develops symptoms around now, we could have another peak,” said Masaru Kinoshita, an official with the Osaka Prefectural Government.

Keiko Taya, an official at the National Institute of Infectious Diseases, explained at an emergency meeting at the airport on Friday that since endemic measles virus transmission has been eliminated in Japan, the disease is believed to have come from travelers passing through the airport. She instructed all airport workers to measure their temperature twice a day — in the morning and at night — and stay away from work if they run a fever or get a rash.

The airport confirmed the first case of the outbreak on Aug. 17. A female worker in her 20s who handles international flights had a fever on Aug. 9. The incubation period for measles is around 10 days, suggesting the woman was infected with the virus at the end of July.

On Aug. 26, another female employee was found to be infected, and the disease has spread mainly among workers at international departure desks.

Measles is highly contagious. If someone who has no immunity to the virus is in the same room as an infected person, the former will most likely get it. Transmission cannot be prevented by wearing a mask or washing hands. The most effective way to prevent its spread is immunization.

The 32 infected are young workers with no immunity for the virus. Kansai Airports is currently checking how many of its 15,000 workers are not immunized.

A 19-year-old male from Hyogo Prefecture who used the airport at the end of July was also diagnosed with measles. After returning from Indonesia, he attended the Justin Bieber concert on Aug. 14 at Makuhari Messe in the city of Chiba, where some 25,000 fans gathered, according to public health authorities and media reports.

Kansai International is crowded with many travelers during the summer, and during the peak Bon season from Aug. 10 to Aug. 21, an average of 60,000 passengers fly in and out of the airport per day.