Story highlights Death toll rises to 8 after thunderstorm asthma incident

Thousands of people hospitalized across Australia's Victoria state

(CNN) A freak illness known as thunderstorm asthma has now killed at least eight people in Australia.

Eight days later, seven people are still receiving hospital treatment, including one who is in a critical condition, according to the Victoria Department of Health and Human Services.

Thunderstorm asthma occurs when a storm hits during a period of unusually high pollen and high humidity, causing the grains to break up and disperse, entering people's lungs and making it hard for them to breathe.

In a survey by the University of Melbourne, 74% of respondents said they experienced an asthma attack during the storm last week.

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