A West Texas jury took but an hour Thursday to acquit a nurse who had been charged with a felony after alerting the state medical board that a doctor at her hospital was practicing unsafe medicine.

The uncommon prosecution had ignited deep concern among health care workers and advocates for whistle-blowers about a potential chilling effect on the reporting of malpractice.

But after a four-day trial in Andrews, Tex., a state court jury quickly found that the nurse, Anne Mitchell, was not guilty of the third-degree felony charge of “misuse of official information.” Conviction could have carried a prison sentence of up to 10 years and a fine of up to $10,000.

The prosecution said Mrs. Mitchell, 52, who had been a nurse at Winkler County Memorial Hospital for 25 years, had used her position to obtain and disseminate confidential information  patient file numbers  in her letter to the medical board with the intent of harming Dr. Rolando G. Arafiles Jr. The prosecutor argued that state law required that reports of misconduct be made in good faith, and that Mrs. Mitchell had been waging a vendetta against Dr. Arafiles since his arrival at the hospital in April 2008.