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On November 21, 2016, a thunderstorm struck Melbourne, Australia. While the expected water and wind damage occurred, the most interesting and unanticipated part of this storm is the dramatic increase in respiratory complaints that followed an otherwise typical afternoon storm. (1, 2,) Emergency dispatchers, EMS, and hospital systems quickly became overwhelmed as calls for help occurred about every 4.5 seconds initially, and treating more than 8,500 patients over the course of two days. Ultimately nine deaths would be attributed to the condition termed “thunderstorm asthma.” (2,3)

Thunderstorm asthma is an increase in acute bronchospasm events following a thunderstorm. This phenomenon occurs during pollen season and is a recognized risk for asthma exacerbations in those with pollen allergies. (4) The condition also occurs in those who have pollen sensitivity, such as hay fever or rhinitis, but are not otherwise considered asthmatics or who have never suffered an asthma attack. (4, 5) Grass pollen grains and fungi are implicated in most ecological studies to date. (5) During the first 30 minutes of a thunderstorm individuals can inhale a high concentration of allergenic material. (6)

There are several theories as to how pollen and fungi are related to respiratory exacerbations following storms. Thunderstorms can cause pollen grains to concentrate at ground level, absorbing moisture and rupturing, then releasing allergenic particles into the air. (4) Thunderstorms also have updrafts and downdrafts of air along with marked temperature changes dependent on elevation. Pollen and fungi can be swept up into clouds via updrafts where the moisture absorption causes rupture above the ground and the micro allergenic particles then fall back to the ground where they are inhaled. The updrafts and downdrafts also cause air outflow from the storm, dispersing micro allergenic particles and increasing the chance of inhalation. (5)

http://apps.startribune.com/blogs/user_images/pauldouglas_1480215028_5.GIF

Updrafts and downdrafts of air within storms also contribute to developing ionic charges with positive ions being released from the ground. These positive ions may attach to pollen and fungi enhancing the rupture potential. (4, 5) Studies show that thunderstorms occurring during elevated pollen or fungi count days and storms with a high lightening content increase the relative risk of respiratory exacerbations. The same mechanism leading to positive and negative charges in a thunderstorm contributing to pollen and fungi rupture also precipitates lightning events. (2, 4, 5) 

Source: http://blogimg.goo.ne.jp/user_image/3b/95/7762659c80d0d63d37f0f19e6fa39a4e.jpg

Thunderstorm asthma was first reported in 1983 in the United Kingdom and subsequently observed in Australia, Canada, Greece, Italy, the Middle East, and the U.S.A. (2, 4, 5) While the exact mechanism in thunderstorm asthma remains unconfirmed, there is observational evidence that links an increase in asthma exacerbations following thunderstorms in pollen season and studies demonstrate an increase in emergency department visits following thunderstorms in pollen season in various locations. (4,5) Temporal associations between thunderstorms and asthma epidemics are known to occur where confounders such as air pollutants are not elevated or are at normal levels. Also people with pollen allergy who remain inside with doors and windows closed during a thunderstorm do not experience an increase in asthma symptoms, and those who have no allergy history do not experience thunderstorm asthma symptoms. (4)

The Australian storm moved across Melbourne on November 21 around 5 P.M. Just an hour later, the EMS system began to answer an unprecedented number of calls related to respiratory complaints. From 6 P.M. to 7 P.M., 510 emergency calls were received, compared to a normal average of 110. Over the next 12 hours the EMS system would answer 2,332 calls. The peak of demand occurred over the span of 15 minutes from 7 P.M. to 7:15 P.M., where 201 emergency calls were received; representing a 593 percent increase in forecasted call volume. Telecommunications responded to this demand by increasing call-taking resources by 28 percent during the first hour and by 94 percent during the second hour of the incident by utilizing shift-change personnel, personnel callback, and redistribution of personnel assets. (2)

EMS cases peaked at 8 P.M. where over 150 cases were pending dispatch of an available resource. General increases in EMS demand were over 30 percent and in priority cases over 70 percent from historical data. Ambulance Victoria employed multiple resources to help meet the demand, such as adding an additional 74 paramedics, five mobile intensive care units, and 17 additional resources from non-emergency contractors. The Melbourne Fire Brigade and Victoria Police also aided in medical response, often with no responding ambulance support. Call volume finally reached normal levels on November 22 at 7 A.M. (2)

Many hospitals reported a 50 percent increase in demand for care over normal daily averages. To meet this demand several strategies were employed, including bringing on additional staff, discharge and readying hospital beds, moving patients from the ED to the hospital who were waiting on admission, creating additional triage and treatment spaces, and setting up clinics specific for respiratory complaints. On November 22 at 11 A.M., with continued presentation of respiratory complaints and even deaths now believed to be a result of respiratory illnesses, the Australian Department of Health and Human Services declared a public health emergency. (2)

Thunderstorm asthma of this scale is unprecedented and represents an unusual and poorly recognized medical phenomenon. (7, 8) Prior to the Melbourne incident in 2016, the largest event occurred in London in 1994. During a 30-hour period starting on June 24, over 640 patients presented to local emergency departments with respiratory symptoms. At least 574 patients had symptoms directly attributable to thunderstorm asthma. (6) This is of particular interest for those involved in preparing medical response plans in areas with a large population base, given the potential for very sudden and substantial increases in demand on both EMS and hospital systems.

Thunderstorms occur in variable geographic areas and during pollen season can contribute to an increase in respiratory complaints. Often this is not recognized as a substantial increase in EMS or emergency department demand at the local level. However, where large populations are involved, this phenomenon can quickly overwhelm the healthcare system and may not be initially recognized as a thunderstorm related event by emergency personnel. Even in an all hazards, community approach to this phenomenon is not generally recognized in emergency management. It is hoped the lessons learned on this occasion in Melbourne can be utilized by health services internationally to aid in the response to similar events in the future.

References:

1. ABC News. Thunderstorm asthma: Two die after Melbourne storm causes spike in respiratory problems. click here. Updated November 21, 2016. Accessed April 12, 2017.

2. Inspector-General for Emergency Management Review. (2017, Feb 1). Review of response to the thunderstorm asthma event of 21-22 November 2016 –Preliminary Report. click here. February 1, 2017. Accessed April 12, 2017.

3. Innis M. (2016, Nov 29).“Thunderstorm Asthma” Kills 8 in Australia. NY Times website. click here November 29, 2016. Accessed April 12, 2017.

4. D’Amato G, Vitale C, Cecchi L, et al. Thunderstorm-related asthma: what happens and why. Clin Exp Allergy. 2016 Mar;46(3):390-396.

5. Dabrera G, Murray V, Emberlin JG, et al. Thunderstorm asthma: an overview of the evidence base and implications for public health advice. QJM 2013 Mar;106(3):207-217.

6. D`Amato G, Maesano IS, Molino A, et al. Thunderstorm-related asthma attacks. J Allergy and Clini Immunol. 2017 Mar 23. pii: S0091-6749(17)30425-6. doi:10.1016/j.jaci.2017.03.003. [Epub ahead of print]

7. Wood S. Thunderstorm asthma: the night a deadly storm took Melbourne's breath away. click here. March 10, 2017. Accessed April 22, 2017.

8. Edwards J. Thunderstorm asthma: Victorian emergency chiefs did not understand crisis, review finds. click here Updated February 2, 2017. Accessed April 22, 2017.

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