see also:

• asthma
• allergens
• Victorian Thunderstorm asthma forecast risk level and grass pollen counts
• Vic Govt funding new research Feb 2017
• The Age: Feb 2017 reporting the Vic Govt's report on the Nov 2016 event
• Vic Better Health patient information on thunderstorm asthma
• Vic Govt public awareness toolkit
• Vic Govt Thunderstorm Asthma webpage

• Thunderstorms may induce a sudden region wide increase in acute asthma in people with a history of allergic rhinitis / hay fever due to rye grass allergy.
• It is thought that the storm conditions are not only associated with wind which increases pollen counts, but also causes the airborne rye grass pollens to burst releasing even smaller allergens as small as 0.1um in diameter which can reach further down the respiratory airways and induce a sudden, severe asthma attack, even in those with no PH asthma.
• A single pollen grain is 10-100um in diameter and contains up to 700 starch granules each measuring 0.6 to 2.5 μm which are coated with grass allergen such as ryegrass allergen Lol p 5.
• In Australia, it mainly occurs in hay fever season when rye grass pollen counts are high - usually October - December.
• An English study published in 1997 showed grass pollen counts of 50 grains/m3/day or more in combination with high sferic (lightning) density significantly increased RRs for asthma admission, suggesting a role for ionization.
• A 2007 English study as well as a 2003 Canadian study also implicated airborne fungi as a trigger factor.
• An Atlanta, Georgia retrospective study showed relative risk of asthma presentations to EDs were greatest if rain or strong winds were associated with the thunderstorm ¹⁾.
• A 2002 report from Canada identified that acute asthma accounted for 5 and 17% of ED visits on thunderstorm asthma days, compared with just 2% on a non-thunderstorm asthma day²⁾.
• It appears that it is not rain nor humidity which cause the pollen to burst in these events but perhaps it is the lightning as per April 2021: Atmospheric modelling of grass pollen rupturing mechanisms for thunderstorm asthma prediction

• Hay fever sufferers often have symptoms in September, well before the rye grass pollens become an issue, these symptoms may be due to other pollens such as:
  • trees such as wattles, cyprus, and birch; and
  • weeds such as daisy (capeweed, Arctotheca calendula) and plantain (Plantago), although many daisies flower later the season over summer.

• counts start to rise in mid-October and peak at end of November and return to minimal levels by end of December ³⁾.
• Grass pollen seasons in Melbourne range from minimal cumulative daily counts of around 1,000 pollen counts (grains/m3) over the season such as occurred in 2015, to over 6,700 which occurred in 1993.
• Severity can be predicted by determining the amount of green in regional rural regions on satellite images.
• An extreme day has daily average pollen counts over 100 grass pollen grains per cubic metre of air.

Melbourne's pollen counts

• Mild events are common in Australia and probably in many other parts of the world
• More severe events:
  • 1983: Birmingham, UK
  • 1987: Melbourne
  • 1989: Melbourne
  • October 1997: Wagga Wagga, NSW
  • 2006?: Naples, Italy
  • Nov 2013: Ahvaz, Iran ⁴⁾
  • Nov 2016: Melbourne and Geelong - over 8,500 asthma cases resulted and 8 died
    • preceded by the highest pollen count season in years - extreme days started on 4th Nov 2016 which had the highest pollen count since Nov 28th 2013 on the back of a particularly wet and cool Spring, and were predicted 3 days in advance of the 21st Nov 2016 when the storm hit causing the extreme unprecedented thunderstorm asthma event