Health authorities have moved about 25 workers exposed to mumps into isolated houses in response to a small outbreak in a Central Washington tree fruit orchard.

Staff from the Grant County Health District also are vaccinating all the employees at the Mattawa, Washington, farm after four workers earlier in the week showed symptoms of the disease, said Theresa Adkinson, Grant County Health District administrator.

The four symptomatic employees are in yet another separate house on the farm. They have sought medical treatment, but nobody has been hospitalized, she said.

Officials call the isolation moves a “limited quarantine,” though the exposed employees may still work every day in the fields, Adkinson said. They are asked to stay in their houses and not interact with the community after work until they go roughly 20 days without exhibiting symptoms.

Adkinson would not name the farm, saying the mumps outbreak was not a widespread public health threat. However, she called the business “extremely cooperative,” helping staff with translations and paperwork during the vaccinations.

The Health District is still investigating who first contracted the disease.

Mumps, a viral disease spread by water droplets from coughing or sneezing, causes fever, swelling and discomfort in the neck and sore muscles. Symptoms can take two to three weeks to appear after infection.

Mattawa, a city of about 4,500, is located in arid Grant County, one of Washington’s leading producers of tree fruit and wine grapes. The population in and around town surges during peak agricultural seasons.

The outbreak involves employees on temporary H-2A visas from Mexico, said Dan Fazio, executive director of wafla, an Olympia, Washington-based agricultural human resources nonprofit responsible for about 75 percent of the H-2A contracts in the state. The farm is a member of wafla, he said, but he would not name it, either.

Most H-2A workers in Washington and the United States come from Mexico, which has a high vaccination rate, higher than that of the U.S. for some diseases. In 2016, Mexico had a 98 percent coverage of the second dose of the measles-mumps-rubella — or MMR 2 — vaccination, while the United States had a 94 percent coverage rate, according to World Health Organization statistics.

Vaccination records are not required for H-2A visas, said Lydia Hock of Labormex, an H-2A recruiter and visa processing agency based in Tamaulipas, Mexico, though the company typically asks for health certificates of prospective workers.

H-2A workers are providing a greater share of America’s farm labor needs each year. In 2018, the U.S. Department of Labor certified 242,762 H-2A workers, nearly three times the amount 10 years ago. Washington was the third highest state behind Georgia and Florida, with 24,862 workers, about 10 percent of the total.

The tree fruit industry is among the highest users of the program.

—by Ross Courtney