Autopsy results suggest poisoning didn't cause the mysterious death of a Canadian woman in Vietnam, but officials won't say what did.

Cathy Huynh, a 26-year-old Vietnamese-Canadian, was travelling with American Karin Joy Bowerman, 27, in the beachside city of Nha Trang when the two fell ill on July 30 and died of respiratory failure.

Officials suspected alcohol or insecticide poisoning.

But a senior officer with the Nha Trang police said Bowerman died of "breathing failures, circulatory collapse due to brain edema," the Tuoi Tre News website reported Tuesday.

Edema is swelling that increases pressure in the skull and can prevent blood from flowing to the brain. It can be caused by head injury/trauma, stroke, tumours and infections like meningitis.

The two women are believed to have died from the same cause.

Police now have the autopsy report on Bowerman, prepared by the Khanh Hoa Forensic Center, but won't release the findings yet, the unnamed officer told the news site.

He also said there were no traces of poison detected in her system, and therefore no grounds for a criminal investigation.

According to the news site, Huynh's family refused to have a post-mortem done on their daughter, saying "one autopsy would be enough."