At about 5:30 pm on the 21st of November 2016 - the peak of grass pollen season in Australia - Victoria was struck by a severe thunderstorm (Lanese 2021).

That evening and the following day, healthcare and emergency services around Melbourne and as far as Geelong were inundated with triple zero calls, emergency department presentations and ambulance requests from people experiencing critical respiratory issues (Lanese 2021; Hughes et al. 2022).

This unprecedented event - the most severe thunderstorm asthma epidemic ever recorded worldwide - resulted in 3,365 extra hospital presentations and 10 deaths (Health.vic 2021; Hughes et al. 2022).

What is Thunderstorm Asthma?

Thunderstorm asthma occurs when high grass pollen levels and a specific type of thunderstorm align, triggering asthma symptoms in certain people. When a large number of people experience these symptoms over a short period of time, such as in the November 2016 incident, this is known as epidemic thunderstorm asthma (Health.vic 2021).

Thunderstorm asthma events are uncommon and difficult to predict as they require very specific weather conditions. However, the highest risk period is during grass pollen season (October to December) (SafeWork NSW 2020).

There have been 24 known epidemic thunderstorm asthma events worldwide, nine of which occurred in Victoria (Connellan 2021).

The prevalence and severity of thunderstorm asthma in Victoria are believed to be associated with specific weather patterns, local plants and Australia having the highest rate of asthma worldwide (Connellan 2021).

What Causes Thunderstorm Asthma?

Thunderstorm asthma is thought to be triggered by inhaling air that contains a high concentration of grass pollen fragments - in particular, perennial ryegrass (NSW Health 2017; National Asthma Council Australia 2017).

While grass pollen is a common cause of allergic rhinitis, whole grains are typically too large to cause any serious issues (SafeWork NSW 2020).

However, the rapid changes in wind, temperature and humidity associated with certain thunderstorms can cause grass pollen to be drawn into the clouds, where they swell with moisture, burst open and disperse into particles that are small enough to penetrate the lungs and cause respiratory issues (SafeWork NSW 2020; Healthdirect 2019; Braitberg 2019).

The greatest risk of exposure appears to be during the strong wind gusts that occur right before rainfall in a thunderstorm, as they can cause grass pollen fragments to become highly concentrated in the air (National Asthma Council Australia 2017).

Risk Factors For Thunderstorm Asthma

Thunderstorm asthma can affect people with no previous history of asthma (SafeWork NSW 2020). However, those at greatest risk include people who:

• Have asthma or undiagnosed asthma symptoms
• Have previously had asthma
• Experience allergic rhinitis, with or without asthma
• Are allergic to ryegrass pollen.

(Health.vic 2021; Healthdirect 2019)

Symptoms of Thunderstorm Asthma

Symptoms of thunderstorm asthma may include:

• Shortness of breath
• Chest tightness
• Wheezing
• Persistent coughing.

(Healthdirect 2019)

Signs that the person is rapidly deteriorating include:

• Difficulty speaking comfortably
• Blue lips
• Loss of consciousness
• Little or no relief from asthma reliever medication.

(SafeWork NSW 2020)

Treating Thunderstorm Asthma

Thunderstorm asthma symptoms can worsen quickly and may become life-threatening (NSW Health 2017).

It's crucial to follow the steps of asthma first aid:

1. Sit the person upright, stay with them and provide reassurance.
2. Administer asthma reliever medication (according to directions and the person’s asthma action plan).
3. Wait four minutes. If there is no improvement, administer asthma reliever medication again.
4. If there is still no improvement, call triple zero (000) for an ambulance and administer asthma reliever medication every four minutes until the ambulance arrives.

(Health.vic 2021)

See: Emergency Asthma Management Lecture

It’s essential to call triple zero (000) and request an ambulance if:

• The person is not breathing
• Asthma symptoms suddenly worsen
• There is no asthma reliever available
• You’re not sure if the person is experiencing asthma.

(Health.vic 2021)

For more information on managing asthma, see Recognising and Responding to Acute Asthma.

Preventing Thunderstorm Asthma

Thunderstorm asthma events are difficult to predict. Therefore, the best way to reduce the risk of severe thunderstorm asthma symptoms is to manage asthma and hay fever throughout the year, particularly during spring (NSW Health 2017).

Those with known asthma should use preventer medicine as directed, carry their asthma reliever, have regular reviews with their general practitioner and ensure their asthma action plan is up to date. People with hay fever or undiagnosed asthma who ‘wheeze and sneeze’ in spring should also seek medical advice in case there are extra precautions that can be taken (NSW Health 2017; Health.vic 2021).

Every person should know the steps of asthma first aid in case someone nearby requires assistance (Health.vic 2021).

Other ways to reduce the risk of thunderstorm asthma include:

• Staying informed about thunderstorm asthma
• Staying inside, closing the windows and setting air conditioners to ‘recirculate’ during spring thunderstorms, especially during the wind gusts preceding rain
• Recognising the signs of an asthma flare-up early.

(Healthdirect 2021)

The following resources can be used to assess the risk of thunderstorm asthma on a given day:

• Thunderstorm Asthma Forecast on the Vic Emergency website (between 1 October and 31 December)
• Bureau of Meteorology
• Pollen Forecast website
• AirRater mobile app.

(Healthdirect 2021)