A state health official has discovered a possible “reservoir” of dengue fever on the Big Island: a pool of migrant farmworkers among whom the disease may be spreading unchecked and who could potentially spread it across the island.

“I’m seeing a parallel universe here, a different group of people,” said Dr. Lorrin Pang, Maui District health director, who has been in South Kona for eight days, driving from farm to farm. “We need to find this group, and I’m afraid it’s kind of in the migrant workers.”

Pang has been on Hawaii island because of his experience in dealing with the 2001 dengue fever outbreak in Hana.

The Department of Health reported Monday 56 people — 10 of whom are children — have tested positive for dengue. That’s up by seven from 49 this weekend. The onset of illness ranges from Sept. 11 to Nov. 7.

The latest Health Department map released this weekend shows that as of Thursday, 33 of 34 dengue cases had exposure in South Kona, a hot spot for the infectious disease. The mauka area of South Kona, where it typically rains in the afternoon, is wetter than other sections of the west side.

The disease is spread by mosquitoes that bite an infected person and transmit the disease to the next person.

While most who tested positive were residents, not farmworkers, Pang suspects farmworkers are not coming forward because they “are very shy, don’t have money, have no health insurance, have no way to get to the hospital.”

He added, “If they don’t work, they don’t get paid and are afraid of having done something illegal.” Some of them may be in the country illegally, he said.

“We’ve worked the last four working days to reach this group, working through churches and community groups, to try to look at dengue in them,” Pang said.

Up to 2,000 migrant Hispanic farmworkers pick coffee in Kona, according to an estimate by a cooperative of coffee farmers.

Pang said this outbreak was very different from the Hana-Nahiku one on Maui, where farmworkers stayed put and the population was small.

“Here they pick coffee and they go to Kona,” he said. When the season is over, they go to Kau to pick macadamia nuts, then they go to Puna.

“If this goes to Puna, where it’s really wet,” it would be difficult to control, Pang said. “I don’t even know how we’re going to address the situation.”

He said it’s still coffee season in mauka areas, but it is ending in the makai farms. In Kau the coffee season is different, so the potential is there for the disease to spread as workers move there.

To illustrate how difficult it is to reach this group, Pang cited the example of a Hispanic worker who tested positive Monday for dengue who was afraid to show up for the first appointment and may have been watching for police. When he finally showed up for a second appointment, the man, despite having an interpreter, “acted like he didn’t hear the question,” Pang said.

The man reported having a headache, fever, body aches and rash, and complained of diarrhea and abdominal pain. He reluctantly said there were four others in his work group, Pang said.

Micronesian workers, who are not illegal, might also not be getting checked because it may not be in their culture to seek health care unless they are very sick, he said.

During community informational meetings, health officials reassured people they were not going to cite them for such violations as marijuana, illegal structures and the like, when officials go on properties to get rid of mosquito-breeding areas.

Pang said that the Big Island outbreak is much different from the 2001 Maui outbreak, where it was a lot easier to get to people.

Driving to coffee farms means taking the main road through Kona, then driving onto side roads, he said.