In most states that have traditionally been hot spots for Lyme disease, the number of confirmed cases of the illness has stabilized or even decreased in recent years, according to a new U.S. government analysis.

Reach for your long pants and bug spray, Pennsylvanians. Our local ticks apparently did not get the memo.

In 2016, the state Department of Health reported 8,988 confirmed cases of Lyme to the U.S. Centers for Disease Control and Prevention, top in the nation and the state's highest toll in recent memory.

Just a few years ago, Pennsylvania's annual totals of Lyme disease — which is transmitted by tick bites and can cause a rash, fever, and debilitating joint pain — were routinely under 5,000. But in 2016, the 8,988 confirmed cases in the state was more than the next four states on the list combined. New Jersey was number two, at 3,332 cases.

A true increase, or just better reporting?

Hard to say, but one thing is clear, said Anne Norris, an infectious diseases specialist at the University of Pennsylvania's Perelman School of Medicine: "We are high achievers with respect to Lyme disease in Pennsylvania," she said.

And there is no official word yet on what happened in 2017, which some experts had warned could be a big year. Norris, who practices at Penn Presbyterian Medical Center, said she saw more cases than usual.

Here is yet another wrinkle. The CDC says the number of "confirmed" cases is likely just a hint of the problem — representing perhaps one-tenth of the actual numbers nationwide.

Pennsylvania has a larger population than many states, so physicians here expect to see a lot of the disease.  But at 70.3 confirmed cases per 100,000 people, the state's rate of Lyme disease for 2016 was also among the national leaders based on population, third after Maine (86.4 cases per 100,000) and Vermont (78.1 per 100,000).

In states where the number of confirmed Lyme cases seems to have stabilized or declined, the true rate may not necessarily have gone down, the CDC said in its Nov. 10 report. The reason may simply be that health officials have cut back the resources devoted to tracking the disease, the agency said.

The CDC defines a confirmed case as meeting one of two conditions:

  • The presence of the kind of rash that is associated with Lyme disease in a person who had exposure to tick habitat or who tested positive for infection. (In some cases, the rash resembles a bulls-eye.)
  • At least one other clinical sign of Lyme disease, such as fever, in a person who tests positive for infection

Diagnosis can be tricky, because the standard blood test, which detects antibodies that the immune system produces in response to Lyme bacteria, yields both false positives and false negatives. That means it identifies some people as having the disease when in fact they do not, and it fails to identify the disease in others who do have it.

In some patients, pain and exhaustion can linger for months, even after the bacteria that cause the disease have been eradicated with the standard course of antibiotics.

Drexel University scientists are attempting to get a better handle on which kinds of ticks are spreading Lyme disease and other types of infections. In late summer, they asked members of the public to mail ticks to their lab, and so far have received several hundred, from as far away as Arizona.