Authorities say a woman found dead along with her infant son in a western Pennsylvania apartment died of pneumonia rather than a drug overdose.

The Allegheny County medical examiner's office said an autopsy concluded that 22-year-old Sara Kessler succumbed to bronchial pneumonia caused by a bacterial infection of the heart in her Millvale apartment in March. Her death was ruled due to natural causes.

Officials said her 9-month-old son, Carey, with no one to care for him, died of dehydration. His death was ruled accidental.

Police said originally that they suspected an overdose, but the medical examiner's office said drugs played no role in her death.

Her brother Matthew Knaus tells the Pittsburgh Tribune-Review that the loss has been eased by learning that his sister wasn't responsible for their deaths.