Australia's summer bushfire smoke killed 445 and put thousands in hospital, inquiry hears

Smoke from the Australian bushfires of the 2019-20 summer caused an estimated 445 deaths and put more than 4,000 people in hospital, a royal commission has heard.

Related: Smoke from Australia's bushfires killed far more people than the fires did, study says

Eighty percent of the Australian population was affected by smoke from the fires, which burned in six states across six months.

Associate Professor Fay Johnston, an environmental health expert from the University of Tasmania, said the health problems from bushfire smoke were much greater than the health impact of the fires themselves.

The total health cost for the 2019-20 season was $2bn, four times higher than the second most severe season for bushfire smoke in 2002-2003.

Johnston told a hearing of the royal commission into natural disaster arrangements that small smoke particles triggered an immune response similar to fighting off an infection, which in people with underlying chronic conditions like asthma or heart disease could cause “serious illness or even death”.

Related: Australia's severe bushfire season was predicted and will be repeated, inquiry told

“If you’re already at higher risk of a heart attack for whatever reason than an increase in particles in the air and the changes your body makes in response to that … can cause a cardiac arrest and can cause death,” she said.

A study overlaying hospital admissions with air quality data, tracking deadly PM 2.5 smoke particles, found 445 excess death attributable to smoke from the 2019-20 bushfires. It also found 3,340 excess admissions to hospitals for heart and lung issues, and more than 1,000 admissions to hospitals for asthma.