Last fall four employees at the hospital fell ill within a short period of time.
In April this year, the prosecutor decided to close the preliminary investigation because it was not possible to prove that any crime had been committed.
Now the police say the preliminary investigation is being reopened.
"It has been reopened at the initiative of the police after information has emerged that they want to look into more closely," says Wayne Seretis, a police spokesperson.
The employees have previously told TV4 that it was salbutamol in liquid form - a bronchodilator asthma medication that in large doses disrupts the body's potassium levels.
