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PITTSBURGH (KDKA) – It used to be rare in this area, but now it is commonplace — the tick-borne, bacterial infection Lyme disease.

It usually shows up as a bullseye rash after a tick bite.

“If left untreated, can progress and more commonly involve arthritis,” says Children’s Hospital infectious diseases specialist Dr. Brian Campfield, “and that can occur weeks to months, sometimes even years after the initial infection.”

Researchers at Children’s Hospital tracked pediatric patient diagnosis codes for Lyme disease and its associated signs and symptoms from 2003 to 2013. They correlated medical records, demographic information, zip codes, and where patients received care.

At first, cases were north and east of Allegheny County.

“But over time, as the rate of disease increased exponentially, we saw a migration in cases. The patients were of closer and closer to the city,” says Dr. Campfield.

As it turns out, kids from rural areas were more likely to see their primary care doctors with symptoms of late Lyme disease, such as arthritis. Children from the suburbs and cities were more likely to be seen in an emergency department for signs of early Lyme disease, such as a rash.

Other corroborating studies have focused on health department records, or ticks and wildlife.

“This is one of the first studies to look at patient records in detail over a broad geographic area, and over time sort of chronicling the disease,” says Dr. Campfield.

The study can’t show why the shift is occurring, though it could possibly be related to migration patterns of deer and mice — the carriers the ticks get it from.

Dr. Campfield hopes the study findings raise awareness of how pervasive Lyme disease is in our area.

“Lyme disease is probably here to stay in western Pennsylvania,” he says, “unless we can come up with some magical way to get rid of, you know, the ticks, and/or deer, or mice, which I don’t think are probably going to go away.”