There is no evidence that people who ate at a New Jersey racetrack have become infected with a rare human version of “mad cow” disease, U.S. health officials said on Friday.

A New Jersey lawyer, Janet Skarbek, had raised questions about what she believed was a cluster of cases of Creutzfeldt-Jakob disease (CJD) among people who had attended the popular racetrack.

CJD is the human equivalent of bovine spongiform encephalopathy or mad cow disease. BSE swept British herds in the 1980s and later a human version, called variant CJD, was found in people who had eaten contaminated beef products.

Both diseases destroy the brain and are caused by a protein called a prion, which becomes malformed and kills brain cells. They are incurable and always fatal.

U.S. agricultural officials said for years that U.S. beef was free of BSE, but several critics said the surveillance system was not adequate for finding cattle with the disease.

In December, a single U.S. cow tested positive for BSE in Washington state, long after it had been slaughtered and processed. Officials found the cow had been imported from Canada, but the incident raised fears BSE could be undetected in the U.S. beef supply.

Skarbek publicized her fears after the December case, and New Jersey health officials as well as the U.S. Centers for Disease Control and Prevention launched an investigation.

“The evidence does not support the existence of an outbreak of CJD among attendees at the Garden State Racetrack, nor does it suggest that case-patients with CJD were exposed to BSE-contaminated beef in the period from 1988 to 1992 at the Garden State Racetrack in New Jersey,” the New Jersey report said.

The issue is confusing because people can develop CJD unrelated to eating beef. So-called sporadic CJD occurs in about one in a million people.

But under a microscope, CJD and the variant CJD linked to eating tainted beef look very different. Health experts are confident they can tell the difference.

“Today’s report indicates that there is no evidence of an increased incidence of CJD associated with the Garden State Racetrack or anywhere in this state,” said Dr. Clifton Lacy, commissioner of health and senior services for New Jersey.

The number of cases is well within the range of expected cases for New Jersey and the United States.”

New Jersey health officials examined the records of 17 people who died in six states: New Jersey, Pennsylvania, Maryland, Connecticut, Virginia and Delaware.

“Of the 17 cases examined in the report, 11 have a definite or probable diagnosis of sporadic CJD and 3 do not have CJD. Three cases are still under investigation pending receipt of patient records,” the report reads.

The patients had a mean age of 67. CJD becomes more common as people get older because it can take decades to develop. CJD is seen in 4 people per million over the age of 55.

“The department has worked closely with the U.S. Centers for Disease Control and Prevention, the National Prion Center, and other states to evaluate the records of these individuals. We are confident in our analysis and conclusions,” said Dr. Eddy Bresnitz, New Jersey state epidemiologist.

The CDC was expected to issue its own report later on Friday