Researchers estimate that smoke pollution probably killed more than 400 people during the unprecedented bush fires across southeast Australia from November to February. Thirty-three people were killed in incidents directly related to the fires.

Air pollution researcher Fay Johnston at the University of Tasmania led a team that collected the average number of emergency department admissions, hospitalizations and deaths on any given day. They then mapped detailed data on air pollution levels from 1 October to 10 February and modelled how these would have increased the emergency admissions.

They found that there could have been as many as 417 additional deaths and 1305 emergency department admissions for asthma attacks over this time. Another 3151 people were also admitted to hospital for heart and other respiratory problems.

The results are reported in the 23 March edition of the Medical Journal of Australia , and are the first published estimate of the scale of the medical impact of the bush fire smoke ¹ . Johnston estimates the haze affected around 80% of Australia’s 25 million people, in some cases for many weeks at a time.

“In terms of the extent and duration of the fires, and pollution in the air, this is off the chart for a single summer fire season,” she says.

Studies such as this one, which estimate the true impact of smoke pollution on the population are important, says Guy Marks, an epidemiologist who studies respiratory diseases at the University of New South Wales in Sydney.

“These deaths and hospitalizations would not have been recognized as being attributable to the fires and smoke at the time they occurred. Hence, they tend to have less attention paid to them,” adds Marks, who was not one of the study authors.