Australian Doctor Australian Doctor 27th October 2017 | Page 27

Therapy Update
Calm before the storm
RESPIRATORY
What lessons have we learnt from last spring’s
deadly asthma event?
PROFESSOR AMANDA BARNARD
A
FTER
last
spring’s epidemic
thunderstorm
asthma
event
in Victoria, the worst ever
recorded worldwide, the
phenomenon is back in the
news ahead of the first grass
pollen season in south-east-
ern Australia. 1
The idea that acute
asthma can be triggered
by thunderstorms is not
new. Several thunderstorm
asthma epidemics have
been documented in Aus-
tralia and overseas since the
1980s. 1-3
Management and preven-
tion is challenging because
people may not be aware
they are at risk, asthma can
have a very rapid onset, the
trigger is practically invis-
ible, and the effects can be
widespread across a region
and population. It is com-
pounded by the fact we do
not yet have well-practised
response protocols.

What is thunderstorm
asthma?
In the medical literature and
the media, the term ‘thun-
derstorm asthma’ is vari-
ously used to mean either
epidemic
thunderstorm
asthma events, or thunder-
storm-triggered asthma in
individuals.
Epidemic thunderstorm
asthma is a cluster of aller-
gic asthma flare-ups associ-
ated with the combination
of high grass pollen counts
and thunderstorms in spring
or early summer. The mas-
sive epidemic thunderstorm
asthma event that occurred
in Melbourne and Geelong
on 21 November 2016
caused a sudden surge in pri-
mary care visits, emergency
ambulance calls, ED presen-
tations and hospital admis-
sions including intensive
care unit admissions. There
was an associated spike in
asthma-related deaths, of
which nine have been inves-
tigated by a thunderstorm
asthma coronial investi-
gation. 1,4
Thunderstorm
asthma epidemics have also
been reported in Canberra,
Newcastle, Tamworth and
Wagga Wagga. 1,5,6
All reported epidemic
thunderstorm asthma events
in Australia have occurred
in October and November.
and release small particles,
which are blown back to
ground level in down-drafts
and dispersed in wind gusts
preceding the rain. 2,7
Known risk factors
Epidemic
thunderstorm
asthma mainly occurs in
south-eastern Australia, but
IN THUNDERSTORM ASTHMA
EPIDEMICS, POORLY CONTROLLED
ASTHMA HAS BEEN ASSOCIATED WITH
THE WORST OUTCOMES.
While the mechanism is
not well defined, the domi-
nant hypothesis is that grass
pollen grains are drawn
upwards into a thunder-
storm, then they rupture
may occur in other regions.
The high-risk period is
October-December.
Risk
factors include:
• 
Ryegrass pollen allergy.
Hypersensitivity to peren-
www.australiandoctor.com.au
nial ryegrass (Lolium per-
enne), a common pasture
crop, has been implicated
in all Australian thunder-
storm asthma epidemics. 5
• 
Seasonal allergic rhinitis
(hay fever) occurring in
springtime, with or with-
out known asthma. In
Australia and internation-
ally, almost all recorded
cases of thunderstorm
asthma (90-100%) have
occurred in people with
a history of allergic rhi-
nitis. 5 It is reasonable to
assume that anyone with
seasonal allergic rhinitis
has ryegrass allergy.
• 
Asthma,
especially
if
poorly controlled. Lack
of
appropriate
regu-
lar inhaled corticoster-
oid treatment appears
to increase the risk. In
thunderstorm
asthma
epidemics, poorly con-
trolled asthma has been
associated with the worst
outcomes
(death
or
life-threatening
asthma
requiring intensive care
admission).
• A past history of asthma.
• 
Exposure to wind gusts
just before and during a
thunderstorm in pollen
season (being outdoors,
or indoors with windows/
doors open).
Questions remain
The precise weather condi-
tions necessary to produce
epidemic
thunderstorm
asthma are unclear. It is
likely that only specific, rel-
atively uncommon types of
storms carry this risk.
Temperature and humid-
ity changes or electrical
charge from lightning may
play a role.
The role of other all