Medical facilities across Pennsylvania are being warned not to open mailings from a New York marketing company because of concerns about a white powdery substance found in some of them.

It's unclear what the powder is. A rapid test on one sample showed a weak positive for botulinum toxin, but testing also shows the powder could just be corn starch, according to an e-mail distributed Wednesday by the Health Alliance of Pennsylvania.

A state lab tested the powder for botulinum and the result came back as "indeterminate," according to the alert. More refined tests were being conducted by the state.

No one exposed to the powder has become ill, the health alliance said. The FBI said that no terror threats have been received.

The company said corn starch was used in the mailing process, the Daily American of Somerset reported in its Thursday editions. A message left with a Positive Promotions spokesman Thursday morning was not immediately returned.

Positive Promotions sent about 4,000 of the mailings this week to hospitals, home health agencies and hospice organizations in Pennsylvania, New York and Ohio, the health alliance said. The Pennsylvania Department of Health asked facilities in the state not to open the letters.