Stemming the tide of dengue fever must go beyond spraying insecticide and telling folks to apply repellent. With Hawaii island’s dengue fever outbreak approaching a public health emergency, it’s critical that authorities become more proactive and test vulnerable populations.

So far, the state Department of Health has confirmed 72 cases of the disease on Hawaii island — 62 residents and 10 visitors — a marked increase from just 33 about a week ago. Further, a DOH official has discovered a possible “reservoir” of dengue fever: a pool of migrant farmworkers among whom the disease may be spreading unchecked. This is troubling given the reluctance of farmworkers, many here illegally, to visit a doctor.

Dr. Lorrin Pang, Maui District health director, has been driving from farm to farm.

“We need to find this group, and I’m afraid it’s kind of in the migrant workers,” said Pang, who is on the Big Island because of his experience in dealing with the 2001 dengue fever outbreak in Hana.

Testing the migrant worker population is crucial given Pang’s observations, and the response needs to be ramped up accordingly to contain further spread.

Up to 2,000 migrant Hispanic farmworkers pick coffee in Kona. When the coffee season is over, they head to Kau to pick macadamia nuts, then go on to Puna, Pang said.

“If this goes to Puna, where it is really wet,” it would be difficult to control.

Dengue fever is spread by mosquitoes that bite an infected person and transmit the disease to the next person, causing fever, rash, aches and other symptoms.

Dr. Virginia Pressler, DOH director, said the department is working with the Hawaii Civil Defense Agency and other responders as part of a unified command. Teams of Emergency Medical Service workers will soon head into underserved communities across Hawaii island. “The beauty of using the EMS team is they will be able to draw blood and collect demographic and medical information,” as well as make sure patients are taken care of, Pressler said.

Because county EMS workers know the community well, Pressler said, “they’re a little more trusted” and would face less resistance. There is no time to waste in launching those teams to get ahead of the outbreak, which has stayed mainly in the island’s southern regions.

A series of community fairs in Hilo, Kona and Pahoa to address populations that have barriers to health care access also is being planned.

State Sen. Josh Green (Naalehu-Kailua Kona) has been a vocal critic of the Health Department, saying its response has lacked urgency.

“If this becomes endemic, it’s going to scare” visitors, said Green, an emergency room physician. “It’s critical that they up their game in testing people locally.”

Green suspects the true number of individuals infected is at least double the amount being reported, and Pressler agreed that the numbers will likely increase. And while Pressler says the situation is not out of control, it is discouraging to see the numbers mounting, a signal that authorities will have to cast a wider net and pool more resources.

The magnitude of the problem will only grow if these pockets of migrant workers are not reached. As an example of the difficulties health officials face, Pang said a Hispanic worker who tested positive Monday for dengue was afraid to show up for the first appointment and may have been watching for police. Micronesian workers, who are not illegal, might not be getting checked because they rarely see a doctor until they are extremely sick, he said.

Telling people to clear stagnant water and slather on mosquito repellent is helpful, but vigorously making inroads within these smaller, rural communities is crucial in staying in front of the outbreak.

Containment is key, and a rapid, comprehensive response is needed to achieve that.