Nurse accused of murdering 13 patients in Italy

A nurse has been arrested on suspicion of killing 13 patients in Italy.

The woman, 55, allegedly committed the murders on the intensive care and anesthesia ward of a hospital where she had worked for decades in Piombino, a city on the Tuscan coast.

Dubbed "the hospital ward killer", she allegedly administered lethal doses of a blood-thinning drug into her victims' intravenous drips between 2014 and summer 2015.

She was held on Wednesday evening after police went to her her home in Pisa after she returned from a holiday with her husband.

The victims, men and women aged between 61 and 88, had all undergone surgery in the state-run facility.

Twelve died of internal bleeding and one of cardiac arrest, police said.

They were each found to have 10 times the normal dose of the drug Heparin in their bloodstream even though they had not been prescribedit, investigators told a news conference.

The nurse was the only person present for all of the surgeries.

None of the patients was terminally ill at the time of the surgeries, which included a routine operation for a broken femur, they said.

A statistical anomaly in the department prompted an investigation by a special health division of the Carabinieri state police last June.

When she became a suspect and was transferred out of intensive care in October last year, the mortality rate of the ward fell from 20% to 12%, Carabinieri police commander Gennero Riccardi told reporters.

Authorities said they had no motive, but confirmed that the nurse had worked in the department for around 20 years and had previously been treated for depression.

The arrest comes just weeks after a court in Ravenna convicted a nurse of killing a 78-year-old patient with a lethal injection. She was sentenced to life in prison.