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Autumn triggers of asthma

Tuomas Jartti MD, Pediatrician, pediatric allergist, Department of Pediatrics, Turku University Hospital, Turku, Finland.
Michael R. Edwards PhD, Senior Lecturer in Respiratory Medicine & Infections, MRC Centre for Allergic Mechanisms of Asthma, Imperial College London, UK.

In autumn 2013, we have again experienced an annual loss in asthma control. The patient, (or patient’s parent) really needs to understand the basic concepts of asthma to prevent this sudden change of control.
First, it is important to understand that asthma is a chronic inflammatory condition of the airways. This inflammation breaks the airway epithelium, produces mucus and increases airway hyperreactivity and oedema. Secondly, if the inflammation is not adequately controlled, many environmental triggers can easily cause asthma attacks or asthma exacerbations. The exact reasons and how allergens and virus infections work together to promote asthma exacerbations is unknown, however EAACI researchers are currently investigating this hot topic.

Virus infections- the importance of rhinovirus

Respiratory viral infections are the most important triggers of asthma during autumn, often resulting in increased hospital admissions associated with asthma. The exact timing of these events may vary between country to country, and region to region, however studies have shown that the beginning of day-care and return to school initiates the effective spread of viruses during late summer and early autumn. Basically, asthmatic and non-asthmatic subjects are exposed to similar amount of viruses, but asthmatic subject are more prone to these infections, and consequently, asthma attacks peak during autumn. Common expressions such as “The September Epidemic of Asthma” or “Horrible October” –provide direct testimony to the burden of morbidity in the form of emergency room admissions and general practitioner consultations that accompany this time of year.
Rhinovirus, the common cold virus, dominates as a causative agent of asthma attacks. In non-asthmatic individuals, rhinovirus infections are usually limited in the nose or may go by as asymptomatic infections. In asthmatic subjects, the broken airway epithelium increases susceptibility to this virus, and consequently, lower airway symptoms, tight cough and expiratory breathing difficulties develop. Unless controller medication is preventively used and/or immetiately enhanced when the first manifestations of respiratory symptmoms appear, the change of control may be sudden and symptoms may persist for a long time.


What about seasonal influenza infections?

Although influenza virus is not so closely associated with wheezing or asthma attacks as many other respiratory viruses, asthmatic subjects may be more prone to respiratory complications, such as pneumonia during or shortly after influenza infection. During influenza season (winter and early spring), asthmatic subjects are typically overpresented at emergency room or hospital wards. It is important that subjects with asthma aged more than 6 months take the seasonal flu vaccination as recommended.

Role of allergens

The persistent or stable (non-exacerbating) form of asthma is usually associated with allergies. Exposure to allergens is an important cause of chronic airway inflammation and may lead to exacerbations depending both on the level of sensitization and exposure as well as the control of inflammation. Pet dander (commonly cats and dogs) is a common perennial allergen. House dust mite plays a bigger role in central Europe and UK than in northern Europe (due to more dry air in the north). Pollen has great geographic variability in Europe. During autumn, weeds and fungi (and moulds) may cause symptoms. Warmer climate in the Mediterranean region causes second flowering of some plants, and mild winter induces pollen from some trees. Overall, pollen, however, plays a less important role during autumn than it does during spring or summer. Summer lightning strikes and thunderstorms are also thought to cause increases in asthma exacerbations, likely helping pollen and moulds to become more aerosolised and more easily to breathe in.

Interplay of virus and allergy

During the last two decades, we have begun to understand the how allergens and viruses interact to promote asthma exacerbations. While allergy usually causes the chronic component of the disease, acute exacerbations are usually accompanied by virus infections. Not only active allergic inflammation in the airways breaks airway epithelium, which provides a physical barrier against viruses, or vice versa, it is also thought to weaken or compromise immunologic mechanisms that exist to fight viruses. Scientific evidence clearly shows this inverse relationship, for example, the higher the IgE sensitization titres are against house dust mite, the more severe the rhinovirus induced asthma attacks typically are. Thus, allergy and virus infection have synergistic actions leading to more severe symptoms than either factors alone. Moreover, airway inflammation also increases sensitivity to nonspecific triggers such as exercise, cold air, and unclean air. Better understanding the precise mechanism at play is likely to lead to better therapeutic strategies for asthma and asthma exacerbations in the future.

Tips to avoid asthma exacerbations during autumn/fall

-    understand what asthma is and how it is treated, e.g. immediately ‘step-up’ in controller medication when the first cold symptoms appear
-    acknowledge and avoid presipitating factors when possible (pet dander, dust mite, indoor molds, transport of pollen to indoors)
-    take the medication as it is prescribed and make sure that the inhalation technique is correct
-    remember to visit your doctor and measure pulmonary function regularly
-    ask your doctor to give you a written self-management plan for asthma and ask whether occasional home peak expiratory flow recordings could be useful to you 

Your asthma is probably in good control when

-    physical excercise is enjoyable without pulmonary limitations
-    common cold symptoms persist less than 2 weeks without major worsening of control
-    occasional peak expiratory flow falls are less than 20-30% of your personal best
-    over a long period of time, bronchodilator is needed less than 2 times a week
-    exacerbation-free periods last 3-6 months