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A breath of fresh air: identifying common triggers for asthma

Charles Broomhead
FRCGP GP
Sutton Coldfield
Honorary Clinical Lecturer
Birmingham University

Asthma is commonly defined as "a chronic inflammatory disorder of the airways and is associated with airway hyper-responsiveness that leads to recurrent episodes of wheezing, breathlessness, chest tightness and coughing".1 The symptoms of asthma in small children may be less specific than in adults, but still usually remain intermittent and can be triggered by a variety of factors.

Most children over the age of three who have asthma are said to be atopic; allergen-specific sensitisation being one of the most important factors for the development of the condition.2 What this means is that, in a sensitised individual, when the bronchial mucosa is exposed to an inhaled airborne antigen, antibodies are produced that bind to mast cells within the bronchial tree. Histamine is released as a direct consequence of this action, causing oedema and the contraction of smooth muscle within the bronchi, both of which reduce airflow. The familiar symptoms of wheezing and dyspnoea then develop, sometimes very rapidly.

Whether the cause of asthma is atopic or not, triggers are not the full story. As we know, attacks of asthma are often precipitated by numerous other causes. Among the most common of these are upper respiratory tract infections, physical activity or exposure to cold air or environmental pollutants. The importance of psychosocial factors in both the development of asthma and in exacerbations is increasingly being recognised although this information may be both difficult to obtain and to quantify.

Information about the patient's individual triggers can play an important role in the diagnosis and management of their asthma. This can often be obtained by taking a careful history from the patient before embarking on tests of lung function or atopy. The results of skin testing are not always reliable nor is it possible to test for all possible allergens. Ritz and colleagues describe a structured questionnaire, which may be useful in exploring the matter further.3

It has been estimated that people spend the vast majority of their lives, perhaps as much as 90%, in indoor environments. Approximately two thirds of that time is spent at home. Many homes offer the prospect of exposure to irritants, such as tobacco smoke, house dust mites, or perhaps cat, dog or other animal hair. In more deprived populations, fumes from heating equipment, cockroaches and mould spores may be particular problems. Young children seem to be particularly vulnerable to these triggers.

Some triggers may be less easy to avoid or control than others. These include psychosocial stress, air pollution or respiratory tract infections, all of these may have a significant impact on both the severity of the patient's asthma, the number of exacerbations and their overall quality of life.
The Seattle-King County Healthy Homes Project used community health workers to minimise exposure to indoor asthma triggers.4

The methods employed included education, support and the provision of resources to lessen exposure. They demonstrated that it was possible to reduce the number of asthma symptom days, to reduce the use of emergency services and to improve the quality of life of caregivers. Interestingly and significantly they showed that more intensive support increased the effectiveness of their intervention.

Management
Once responsible triggers have been identified, it may be possible to effectively reduce the patient's exposure to them and thereby improve the quality of their care. Some of the possible interventions are relatively inexpensive and simple, although not always easy or popular to implement.

Tobacco smoke
The very first and most important thing to do is to stop exposure to tobacco smoke. There should be no excuses and no exceptions! Studies have shown that children living in a household where there is a smoker are significantly more likely to have asthma than those residing in a smoke-free environment.

If the patient themselves is a smoker, they should be offered effective advice about quitting and strongly encouraged to do so. Passive smoking in the workplace should now be a thing of the past but may still occur at home or in private motor vehicles. Every effort must be made to overcome this. If the patient is not a smoker, they should be very strongly advised never to take up the habit.

Respiratory tract infections
There is little that can be done to avoid upper respiratory tract infections, although these are a common trigger for asthma. Most will be viral in origin and, consequently, unlikely to respond to antibiotic therapy. Perhaps the most important thing to remember is that the exacerbations need adequate treatment and that amoxicillin is not a bronchodilator!
Once again, tobacco smoke is implicated in a survey of more than 7,000 children and adolescents under 18 years of age, those whose mothers smoked were more likely to experience wheezing respiratory illness than children with nonsmoking mothers.

House dust mites
House dust mites are found almost universally in our homes, particularly in clothes, beds, cushions and carpets. They are about 0.3 mm in size so are invisible to the naked eye. Respiratory symptoms are triggered in sensitive people by breathing in the mites' droppings. It is probably impossible to get rid of all house dust mites within a home but their numbers and their effects can be reduced significantly.

Nocturnal exposure in the bedroom is usually the biggest problem and while the greatest attention may be focused here, for the best results, the whole house should be treated.  
Ventilation is very important as house dust mites thrive best in warm, damp conditions. Simply opening a bedroom window may improve things considerably. Airing the house will also serve to discourage mould growth; the spores of which are common triggers.

General measures include regular dusting and vacuum cleaning. Unfortunately most conventional vacuum cleaners are relatively inefficient at filtering fine dust and may simply recycle the allergenic particles back into the air, effectively exacerbating the problem. Consideration may ultimately need to be given to acquiring a machine with a high efficiency particulate air (HEPA) filter but this should usually be a last rather than a first resort as other measures may prove effective.

In general, laminate or vinyl flooring is likely to harbour many fewer house dust mites than carpets and, expense allowing, this is something that might be considered.

As mentioned previously, particular attention should be paid to the bedroom. Leaving the bed "open" to air before remaking it can be effective, as can using the vacuum cleaner on the mattress and pillows where there will be large numbers of skin scales. Similarly, the mattress and pillows may be enclosed in a dust mite-proof cover, which can be wiped clean on a regular basis. Washing bed-clothes and pillows at a temperature of 60OC or more will kill house dust mites, so using bedding that can be treated in this way is desirable.

Soft toys often represent a particular problem, as just like pillows they are likely to harbour significant numbers of mites. A susceptible child cuddling his favourite toy at night and inhaling dust mite droppings from it is almost certain to experience symptoms. While it may be possible to change pillows regularly, disposing of a much loved teddy bear may be much more difficult! Similarly, most soft toys are unlikely to survive high temperature washing. An alternative and effective strategy is said to be to place the soft toy in a domestic freezer for about six hours to kill the house dust mite and then to wash it gently to remove the remaining faeces.  Monthly treatment is probably necessary.

Chemical treatments (acaricides/antigen denaturing compounds) are available to kill house dust mites in soft furnishings but, in general, their effectiveness has proven disappointing. Certainly, they are likely to be expensive, and simpler, safer approaches should be used before resorting to their use.

A great deal of useful, simply presented information is available at housedustmite.org for those patients wanting to know more about this problem.

Animals
Household pets, both feathered and furred, are common triggers for asthma. The allergens are found in their saliva, dander, fur, feathers and urine.

Although the psychological benefits of contacts between animals and their owners are well known, where it is recognised that the relationship triggers asthma, the only sensible course of action must be to find a new home for the pet. If this is impossible, or the prospect causes too much distress, ensuring that they are excluded from living areas, in particular the bedroom, may improve things. Avoiding visiting a friend or family member who has the offending animal may sometimes be necessary, although this is something that demands a degree of tact!

It is sometimes said that regular, frequent bathing (perhaps twice weekly) of cats and dogs may reduce the severity of the problem.

Once an animal has been removed from the environment, thorough cleaning of the house is essential as allergenic residues can persist for a long time - perhaps years. This may explain why somebody moving into a new house where the previous owners have kept an animal may start to experience
asthma symptoms.

Other triggers
For some asthmatics, exercise acts as a trigger for their symptoms. Except in extraordinary circumstances, exercise is to be commended for its overall health benefits and therapy should be adjusted to overcome the problem. There is some evidence that oesophageal reflux may promote a nocturnal cough or symptoms of asthma. Measures to reduce reflux or treatment with a proton pump inhibitor are
often effective.

Summary
There are many common triggers for asthma and although some are difficult to avoid there are others however which may be modified or avoided with a little effort. Addressing these may significantly improve the overall control of the asthmatic's condition; reduce the need for both regular and emergency treatment. Quality of life is likely to increase and admissions to hospital to be reduced.

References
1. Global Initiative for Asthma (GINA). Global Strategy for Asthma Management and Prevention (updated 2008). Bethesda (MD): GINA; 2007.
2. Sly PD, Boner AL, Bjorksten B et al. Early identification of atopy in the prediction of persistent asthma in children. Lancet 2008;372:1100-6.
3. Ritz T, Steptoe A, Bobb C, Harris AH, Edwards M. The asthma trigger inventory: validation of a questionnaire for perceived triggers of asthma. Psychosom Med 2006;68:956-65.
4. Krieger JW, Takaro TK, Song L, Weaver M. The Seattle-King County Healthy Homes Project: a randomized, controlled trial of a community health worker intervention to decrease exposure to indoor asthma triggers. Am J Public Health 2005;95:652-9.