New data from the U.S. Centers for Disease Control and Prevention indicate that cases of tick-borne Lyme disease might be as much as 10 times higher than official records.

The CDC published a report last week that suggests an estimated 476,000 Americans contract the illness every year, not the 35,000 or 40,000 annually that has previously been reported.

Maine has the highest incidence rate of Lyme disease in the nation, in large part because deer ticks are particularly active here. Cases have been steadily increasing in Maine and reached a record of 2,079 in 2019, although as the recent data suggest, that number could be as high as 20,000 cases.

Disease experts have always known that actual cases are far higher than what is reported by state health departments. The latest estimate from the CDC was arrived at by reviewing billing codes on health insurance claims from 2010 through 2018. Researchers first counted cases that were officially coded as Lyme disease, and for which the patient received antibiotics, then used statistical tools to estimate cases among all people, including the uninsured, those age 65 and older who would not be included in commercial insurance claims data and those who were never treated. The CDC also said previous research suggests that Lyme is not always coded correctly, in part because it’s difficult to diagnose. There is no definitive test to detect the disease; it must be diagnosed by a clinician based on symptoms.

Sen. Susan Collins of Maine, who in 2019 co-authored the Kay Hagan Tick Act, said the new estimate “underscores the fact that tick-borne illnesses are a serious and growing public health threat.”

“Now that we have a clearer picture of the challenge that we are up against, we are better positioned to protect Americans’ health,” the Republican said in a statement.

As part of that 2019 legislation, which included $100 million in funding over five years to combat the disease, the CDC has unveiled a new dashboard to help researchers collect real-time data from emergency room and walk-in clinic visits. It will be updated weekly to better indicate when people in different parts of the country may be at the highest risk.

Lyme disease is caused by a bacterial infection transmitted by the bite of a deer tick. If caught early, the infection can be treated with antibiotics. Symptoms include a bulls-eye rash – which occurs in about 50 percent of patients – fever, chills, headache, muscle and joint aches, and neurological problems, such as Bell’s palsy. Lyme is the most common tick-borne illness, but the CDC tracks others as well, including anaplasmosis and babesiosis, which also have been seen increasingly in Maine.

Last year, the University of Maine Cooperative Extension Tick Lab conducted a first-of-its-kind survey on tick and tick-borne diseases. Researchers found that about 40 percent of almost 2,000 deer ticks submitted by volunteers and tested last year were infected with Lyme disease. Eight percent of ticks carried anaplasmosis and 6 percent carried babesiosis. The report included samples submitted by residents from each of the state’s 16 counties, and from 358 municipalities, and were collected between April 1 and Dec. 30, 2019.

Adult deer ticks are most active from early spring to late fall with peaks in April or May and in late October or early November, the report said. Nymph numbers usually peak in June and early July. Deer ticks can remain active as long as the temperature is above freezing, and recent research suggests that they can survive under leaves and snowpack, even if the surface temperature stays cold.

Experts urge people who go into tick habitats such as woods and fields to wear pants and long-sleeved shirts, apply bug repellent and conduct frequent “tick checks” to see if they’ve picked up any ticks while being outside. Around the house, it’s wise to reduce the number of yard leaves and be careful of wood piles or dead wood, where ticks can congregate.