Discussion
We present a comprehensive longitudinal study of anaphylaxis in Hong
Kong over a span of 11 years. With the availability of our
territory-wide electronic clinical information system, we were able to
calculate the near-absolute anaphylaxis incidence of 3.57 per 100,000
person-years, with an apparent rise in anaphylaxis incidence over the
past decade from 2009 to 2019. In contrast to previous reports, this
incidence is comparable to Western populations and we identified a
discrepancy of AAI prescription rates between adult and paediatric
anaphylaxis survivors.
Although it is difficult to directly compare between studies due to
differences in study design and anaphylaxis definitions, our findings
are consistent with reports from Western cohorts. For example, the
national anaphylaxis data from the UK between 1992 to 2012 found an
increase in anaphylaxis admissions from 1 to 7 cases per 100,000
population per annum 12. The estimated anaphylaxis
incidence rates were 1.75 per 100 000 person‐years from the Spanish
hospital system during the period 1998-2011 and 1.41 per 100,000
person-years from the Chile’s hospital discharge database between 2001
and 2010 13,14. The incidence rate of anaphylaxis in
Olmsted County, Minnesota of the United States was, however, much higher
at 42 per 100,000 person-years from 2001 to 2010 15.
Our novel findings show that Asian populations have also seen a parallel
and comparable rise in anaphylaxis incidence to Western cohorts over the
past decade. Well‐designed prospective studies using a standardized
working definition as well as a unified reporting and collection method
of anaphylaxis data are much needed in Asia to better understand how
genetic and environmental factors modulate anaphylaxis susceptibility.
Identification of potential ethnic- or population-specific modulators
may elucidate novel protective or pathomechanisms of anaphylaxis. For
example, differences in susceptibility to specific co-factors or
adherence to allergen avoidance among different ethnicities have been
implicated 16. Such findings would be invaluable to
inform future allergy prevention or treatment strategies both locally
and internationally.
Reports on the adherence of AAI prescriptions across different centres
and countries. For example, the rates of AAI prescription or retrieval
were 54-68% in Olmsted County of the United States; 69.9% in Manitoba,
Canada; and 76% in a report from Denmark 17,18. In
contrast, we identified that fewer than 15% of our anaphylaxis patients
were prescribed with AAI. We were also able to confirm that all AAI
prescriptions were dispensed and retrieved by patients due to the
integration of pharmacies into our public healthcare system. Although
there was a gradual improvement in AAI prescription rates (especially in
adults) over the past decade, over 70% of patients surviving
anaphylaxis in 2019 were still not prescribed with AAI. Since our study
only reviewed patients’ discharge medications, the true rate of AAI
possession by anaphylaxis patients may be under-estimated as AAI may be
prescribed upon subsequent review by allergists. However, as per most
international recommendations, AAI should be prescribed for at-risk
patients upon discharge from the ED or hospital 19-21.
This is particularly important when there is a time lag between the
allergic or anaphylaxis episode and subsequent allergy consultation. The
alarmingly low rate of AAI prescription in Hong Kong was, however,
worrisome as more than 10% of adult patients with anaphylaxis did not
have an identifiable cause and were reported to have lower adherence to
dietary avoidance compared to Western cohorts 16. Our
findings therefore heed for an urgent call to improve allergy resources
and physician education for anaphylaxis. For example, local or
institutional recommendations need to be available and reinforced to
optimize the rate of AAI prescription and training among anaphylaxis
survivors before discharge. All at-risk patients should also be referred
(and timely reviewed) by allergists for accurate diagnosis and
counselling to prevent recurrent life-threatening episodes in the
future.
Our study identified a discrepancy of anaphylaxis care between adult and
pediatric patients. During the past decade, pediatric patients were
significantly more likely to be prescribed AAI compared to adult
patients as shown in our multivariate analysis. In 2009, less than 1%
of adult anaphylaxis patients was prescribed an AAI, compared to more
than 25% of pediatric patients. Although the rate of AAI prescription
subsequently improved for both adult and pediatric patients, only 16%
of adult anaphylaxis patients in 2019 had AAI compared to 64% of
pediatric patients. We postulate that this may be due to perception of
hospital-based physicians that adult patients may be at lower risk of
anaphylaxis recurrence due to better allergen avoidance, or lack of
local adult allergists 22. It may also be attributed
by the heightened awareness of anaphylaxis in pediatric physicians as
allergic diseases, particularly food allergy and eczema, usually occur
in the first few years of life 23. Survivors of
anaphylaxis are at continuous risk of repeated life-threatening
episodes, with previous studies reporting one in twelve patients
experiencing recurrence and one in fifty requiring adrenaline or
hospital attention 24. Food-induced, exercise, and
“idiopathic” anaphylaxis have been reported to have even higher
recurrence rates 24-26. Our study highlights the dire
demand of allergy services, especially for adult patients presented to
ED and hospitals for anaphylaxis.
Our study also noted a sharp increase in anaphylaxis incidence from 2013
to 2014. This coincides with the year with the most marked anaphylaxis
fatalities in the United States, and the year when the updated practice
parameter for food allergy was issued 2,27. Altogether
this might have led to the heightened awareness of anaphylaxis in the
community and related professions, as well as a shifting behaviour and
practice in our patients and health care providers. This demonstrates
the importance of continued physician education and promoting
anaphylaxis awareness in the community.
The strength of this study is that we used a population-based data set
with detailed time-trend, age and sex distribution analyses. However,
one of the limitations of this study was the inability to capture
information about the anaphylaxis triggers due to the privacy
regulations in a deidentified study. Also, data may be incomplete if we
identify anaphylaxis triggers based on ICD-9 coding, since causes of
anaphylaxis may not be apparent upon initial presentation, but only
confirmed after detailed allergy assessment. Our study could not capture
patients who do not present to emergency services, but would only be a
small proportion and is a limitation common in other studies28. Another limitation of this study is that
anaphylaxis-related fatalities were not identified/reported, again
highlighting the under-recognition of anaphylaxis in our community.