(j) Standard: Uses and disclosures to avert a serious threat to health or safety -
(1) Permitted disclosures. A covered entity may, consistent with applicable law and standards of ethical conduct, use or disclose protected health information, if the covered entity, in good faith, believes the use or disclosure:
(A) Is necessary to prevent or lessen a serious and imminent threat to the health or safety of a person or the public; and
(B) Is to a person or persons reasonably able to prevent or lessen the threat, including the target of the threat;
In addition to what Anthony posted, our state has mandated reporter laws, which means not only do you have the right to report, but you must report.
I'd check our your state requirements to see what laws are in place.