Beloved actor Catherine O’Hara’s sudden death was caused by a pulmonary embolism – a condition that affects hundreds of thousands of people each year and saw tennis star Serena Williams hospitalised in 2011.

A Los Angeles County death certificate issued on Monday (local time) listed the embolism as the immediate cause of the Schitt’s Creek star’s death on January 30, with rectal cancer as the long-term underlying cause.

A pulmonary embolism is caused by a blood clot that forms in a person’s leg or pelvis (called deep vein thrombosis or DVT) and then travels through the bloodstream and lodges itself in their lungs, according to Thrombosis Australia.

“A pulmonary embolism is particularly dangerous as it can damage your lungs and result in low oxygen levels in your blood – something that can damage other organs or even cause death,” says the organisation’s website.

The Australian Bureau of Statistics website notes that it is rare for a pulmonary embolism to occur spontaneously in anyone aged under 75.

Its guidelines say there are “a large variety of underlying causes” of the condition, which should be included on death certificates as appropriate.

The oncologist who signed O’Hara’s certificate indicated that he had been treating the Canadian actress since March last year and most recently saw her on January 27.

The 71-year-old, who died at a hospital in Santa Monica, California, starred as Macaulay Culkin’s mother in two Home Alone movies, won an Emmy as matriarch Moira Rose in the long-running comedy Schitt’s Creek and was also known for her roles in films such as Beatlejuice and Best in Show.

O’Hara’s death – first reported as having occurred “following a brief illness” – shocked fans and prompted an outpouring of tributes from both Hollywood stars and viewers.

 

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Thrombosis Australia reports that venous thromboembolism – which includes pulmonary embolism and deep vein thrombosis – is the third-most common cardiovascular disease, affecting 10 million people around the world.

Pulmonary embolism and DVT together reportedly affect about 900,000 people in the United States every year, while an article on an Australian government website states that more than 17,000 Australians annually will have an embolism of some type, with the incidence increasing as our population ages.

Tennis star Serena Williams suffered a pulmonary embolism in 2011, and said at the time that she was lucky to survive after doctors found several blood clots on her lungs. She had been on her way to an Oscars party when she started having trouble breathing, and went to hospital only at her physiotherapist’s insistence.

“I was on my death bed at one point – quite literally. I’ve had a serious illness but at first I didn’t appreciate that,” she said.

A medical expert told ABC News in America after Williams’ health scare the she would have been at increased risk of DVT after a foot injury that had left her incapacitated and a long flight, adding that pulmonary embolism was surprisingly common.

“Prior surgery, air travel, prolonged sitting, birth control pills, obesity and pregnancy can predispose a patient to a blood clot in the leg that can travel to the lung,” said Mark Adelman, chief of vascular surgery at New York University Langone Medical Centre.

Pulmonary embolism was listed as the cause of death for artist Frida Kahlo, who had been bedridden since a bus accident at just 18, while film star James Stewart died at 89 after a thrombosis on his leg caused a pulmonary embolism.

People who have cancer or are hospitalised or bedridden with another serious illness are at increased risk of suffering DVT and pulmonary embolism, with other potential risk factors including genetic conditions, immobility, older age, obesity, smoking and major surgery.

While the symptoms of DVT include leg pain or swelling and red or blue skin discolouration, pulmonary embolism symptoms range from difficulty breathing and chest pain, to fainting, a rapid heart rate and coughing up blood.

“A pulmonary embolism is a serious condition,” states Australia’s Heath Direct website.

“It can be life-threatening if not treated quickly. If you think you may have a PE, you should see a doctor straight away.”

It says the main treatment is anticoagulant medicine (blood thinners), which reduce further blood clotting, and thrombolytics, used to break down and dissolve the clot.

More information, including steps that can help reduce the risk of developing DVT or pulmonary embolism, can be found on the Thrombosis Australia and Health Direct websites