Thousands of people were hospitalized from a rare outbreak called thunderstorm asthma on Monday in Melbourne and other parts of Australia. Eight people were confirmed dead in Melbourne due to this illness.

Thunderstorm asthma strikes when a storm hits during a high humidity and excessive level of pollen period, leading to breathing problems as a result of a  rare combination of weather and pollen. This disease affects everyone, from those who had no history of asthma to those with an acute asthma.

According to the University of Melbourne, 74% of respondents said they suffer from an asthma attack during last week's storm, as reported by CNN.

 Unusually high level of tree pollen and fungal spore can be one of the main causes of asthma attack, even though grass pollen is the most familiar cause of thunderstorm asthma. However, the case can vary based on geographical location, according to Aziz Sheikh, Professor of Primary Care Research and Development at the University of Edinburgh. He added that pollen from olive tree was the cause of asthma attack in Italy in 2010.

The government had deployed an extra 60 ambulance cars to respond more than 1,900 emergency calls in four hours. One man described he is feeling like there is an elephant standing on his chest, as ABC reports.

Experts are now studying this illness while health authorities, meteorologists, botanists, and doctors are now trying to identify the causes of last week's phenomenon so they can issue a warning and predict what is happening soon.

People who cough, sneeze during the storm period should consult the doctor to make sure whether it is asthma, allergy, or other illness. Further testing is necessary to examine the symptoms.

Melbourne's "thunderstorm asthma" outbreak is the most fatal in global history and could may change medical recommendation for hay fever sufferers and asthmatics, according to experts.