Asthma

Asthma is characterised by paroxysmal and reversible obstruction of the airways. It is increasingly understood as an inflammatory condition combined with bronchial hyper-responsiveness. Acute asthma involves:

  • Bronchospasm (smooth muscle spasm narrowing airways).
  • Excessive production of secretions (plugging airways).

Triggers unleash an inflammatory cascade within the bronchial tree leading to the typical symptoms of asthma, e.g. wheeze, shortness of breath, chest tightness, cough. Even in asymptomatic periods, asthmatic lungs show evidence of inflammation compared with controls and there is much interest in how chronic or repeated episodes of inflammation may cause 'remodelling' of the airways and supporting vasculature, leading to disease progression.1



Acute severe asthma (status asthmaticus) can be life-threatening and the disease causes significant morbidity so it is imperative to treat energetically. The bulk of asthma management has taken place within primary care. Since 2004, it has been an important component of the Qualities and Outcomes Framework of the new General Medical Services

Epidemiology

  • Undoubtedly, asthma is a very common condition and currently, according to Asthma UK:3
    • 5.4 million people in the UK receive treatment for asthma: 1 in 10 children and 1 in 12 adults.
    • It is the most common chronic medical condition in children.
    • There are 4.1 million GP consultations for asthma per year.
    • The cost of asthma to the NHS runs at about a billion pounds per year.
  • Internationally, the UK is one of the highest ranking countries in terms of asthma prevalence, hospital admissions and mortality.
  • Peak prevalence occurs between the ages of 5 and 15, and falls thereafter until aged 55-64 years, when it starts to rise again.
  • Gender differences - there is a male preponderance in childhood with a reversal in early adulthood.
  • Certain trends in the prevalence of asthma seem apparent over time,4 but their interpretation is difficult, given methodological difficulties (variation in methods of data collection and classification) as well as cultural artefact from changes in the way patients describe respiratory symptoms and the 'ease' with which doctors apply the diagnosis.5
    • Asthma diagnoses have become much more common since the 1950s, with childhood prevalence increased by two to three times.
      The trend in childhood prevalence appears to have flattened or even fallen recently whilst it remains plateaued in adults.
    • Incidence (based on new asthma diagnoses from the GP) has risen in all ages to a plateau in the 1990s and subsequently fallen.
    • Hospital admission rates rose from the 1960s to the late 1980s and are now falling.
    • There was an asthma death 'epidemic' in the 1960s, particularly amongst children and young adults. This has been ascribed to treatment-related changes. A second, more gradual peak was seen in the 1970s-1980s in adults and mortality has tended to decline since.

The numbers within an individual practice, based on an age/sex/disease register, tend to overestimate true prevalence significantly, as many outgrow asthma without the removal of the diagnosis. It should be changed to past history of asthma when a patient is no longer receiving treatment for the condition.

Overlap between chronic obstructive pulmonary disease and asthma

It is well known that chronic obstructive pulmonary disease (COPD) and asthma are almost identical illnesses with similar presentations. Yet there has been recent research which has shown that these two disorders have similar genetic origin and minor changes in the same gene can have positive effects on both asthma and COPD, e.g. matrix metalloproteinase 12.6,7 More work is ongoing in this area.

Risk factors

There is a long list of possible risk factors but research is frequently contradictory or confounded:8

  • Personal history of atopy.9
  • Family history of asthma or atopy.9
  • Inner city environment.
  • Socioeconomic deprivation.
  • Obesity.10
  • Prematurity and low birthweight.
  • Viral infections in early childhood.
  • Maternal smoking.
  • Smoking.11
  • Early exposure to broad-spectrum antibiotics.12

Possible protective factors include:

In years to come it may be possible to determine risk by the use of exhaled or genetic biomarkers.15

Presentation

The history is extremely important as patients may present between acute attacks when examination and investigation may be completely normal. The paroxysmal nature of the condition is important.

Wheezing or rhonchi is seen as the cardinal feature but this can be misleading. Ensure that the patient or their parent/carer's understanding of 'wheeze' is the same as yours - whistling, squeaking or gasping sounds, or a different style, rate or timbre of breathing are all sometimes described as 'wheeze' so it is important to clarify. Also, wheeze can be absent in severe asthma when there is insufficient air flow to cause wheeze - beware the silent chest.

Ask what happens in an attack. There are a number of possibilities:

  • Wheezing - common but not invariable.
  • Coughing.
  • Shortness of breath.
  • Chest tightness.

Ask if there is an obvious precipitating or aggravating factor for attacks:

  • Cold symptoms - upper respiratory tract infection (URTI) - frequently trigger exacerbations.
  • Cold air - if this causes chest pain in an adult, it may be angina.
  • Exercise - symptoms may occur during exercise but more classically after exercise. Running is worse than cycling and it is uncommon when swimming.
  • Pollution - especially cigarette smoke.
  • Allergens - exacerbations may occur seasonally around pollen exposure or following exposure to animals such as cats, dogs or horses.
  • Time of day - there is a natural dip in peak flow overnight and in a vulnerable person this may precipitate or aggravate symptoms. It may cause nocturnal waking or simply being rather short of breath or wheezy in the morning.
  • Work-related - if symptoms are better at home/during holidays, then asthma may be related to occupation. This has significant implications and it is sensible to refer the person to a chest physician or an occupational physician. See separate article Occupational Asthma.

Past, present and family history

  • Atopic eczema, asthma and hay fever tend to run together in individuals and in families.
  • Ask about medication - the patient may have been started on a betablocker recently (including drops for glaucoma) or taken anti-inflammatories. The association between non-steroidal anti-inflammatory drugs (NSAIDs), including aspirin, and the precipitation of asthma is well documented but, in reality, it is not often seen.
  • Ask about smoking, including passive smoking.

Examination

See separate article Respiratory System - History and Exam. The chest should be examined but this may be normal between attacks:

  • Before examining the chest, check the pulse rate. This may be artificially elevated by excessive use of beta2-agonists but, nevertheless, tachycardia is a significant feature. Respiratory rates above 25/minute and heart rate above 110/minute are regarded as significant signs in adults.9 Where available, also check oxygen saturations in acute attacks (saturations of <92% indicate a more severe subgroup of patients who may require admission).
  • Look at the patient's breathing:
    • Is it fast?
    • Is it laboured?
    • Do they appear anxious?
    • Can they speak in full sentences?
    • Are accessory muscles of respiration employed?
    • Is there pursed lip breathing?
    • Is there cyanosis?
  • Note the ratio between the inspiratory and expiratory phase. Usually this can be assessed by counting one on the way in and one, two on the way out. This 2:1 ratio of expiratory to inspiratory phase is normal. The longer the expiratory phase compared with the inspiratory phase, the more severe the obstruction.
  • The chest may appear hyperinflated.
  • With chronic asthma, there may be chest deformity, e.g. Harrison's sulci.
  • In a small child, there may be intercostal recession with respiratory distress.
  • Check that there is no deviation of the trachea or abnormalities on percussion to suggest pneumonia, pulmonary collapse or pneumothorax.
  • There may be diffuse expiratory rhonchi. If they are not diffuse and particularly if asymmetrical in a child, be suspicious of inhaled foreign body. There may be inspiratory rhonchi too. Where rhonchi are predominantly inspiratory and the inspiratory phase is prolonged, this suggests that airway obstruction is outside the chest.

Differential diagnosis

Asthma is a very common condition but there are many other diagnoses that must be considered: 'not all asthma wheezes and all that wheezes is not asthma'. See separate article Wheezing in Children.

Children

  • Especially if the problem appears to have been present since birth, consider cystic fibrosis. It may also cause severe infections and a persistent cough.
  • Other congenital problems may present from birth or early in infancy, e.g. laryngeal or tracheal structural abnormalities, congenital heart disease.
  • Vomiting and aspiration in babies suggests gastro-oesophageal reflux which can cause a cough on lying down.
  • Inhalation of a foreign body can occur at all ages from the orally curious infant to the performing, older child catching peanuts or grapes in their mouth. Peanuts tend to go straight down to the right main bronchus and cause considerable inflammation, and obstruct the right lower lobe. The choking episode may not have been observed by an adult or may have occurred sufficiently long ago for the family to have forgotten it.
  • Postnasal drip causes a cough, which is worse at night.
  • Inspiratory stridor and wheeze suggest a laryngeal disorder including croup.
  • Focal signs may suggest bronchiectasis or tuberculosis. The latter is very important if the child is from a high-risk family.

Adults

  • COPD - reversibility distinguishes asthma from COPD, although the reversibility is relative rather than absolute: people with severe asthma may never achieve completely normal parameters for lung function and COPD is rarely totally refractory to medication. See separate article Diagnosing COPD. Almost all patients with COPD do smoke or have smoked in the past. Asthmatics can also develop COPD. Whether or not this reflects disease progression or comorbidity is debatable.
  • Heart failure can cause nocturnal cough and cardiac asthma.
  • Ischaemic heart disease - chest tightness or pain, especially on meeting a stiff wind on a cold morning - may be asthma or angina.
  • Malignancy is important to remember, especially in smokers. Look for clubbing which also occurs in bronchiectasis. Malignancy is not just lung cancer but may be in the upper airways.
  • Gastro-oesophageal reflux can cause nocturnal cough and a postnasal drip may cause more coughing when lying down.
  • Other less common causes of chronic cough, wheeze or breathlessness include pulmonary fibrosis, interstitial lung disease, recurrent pulmonary embolism and tuberculosis.

Distinguish wheezing from shortness of breath on exertion - this can be due to heart failure, severe anaemia and obesity, often aggravated by lack of physical fitness.

Investigations


Peak flow

Measurement of peak expiratory flow rate (PEFR) is the simplest and most basic test. Every GP should have a mini Wright's peak flow meter with disposable mouthpieces, and a smaller, low reading one is often useful for children and for more severe obstruction. Caution should be used when diagnosing asthma based on peak flow readings but it has an important role in the management of established asthma.

Lung function tests, whether peak flow or spirometry, are unreliable below the age of 5 years and even among some older children and adults who lack comprehension or co-ordination for the task. As well as obstruction of airways, poor effort or neuromuscular disease will limit performance. In those able to use a peak flow meter reliably, it is often helpful to prescribe a peak flow meter for home use to encourage self-monitoring and adjustment of treatment in line with a self-management plan.

Technique

  • Peak flow is usually estimated with the patient standing, although results are not significantly different if the patient is seated.16
  • Advise the patient to take in a deep breath and expel it as rapidly and as forcefully as possible into the meter.
  • The very first part is all that matters for this test and it is not necessary to empty the lungs completely.
  • Record the best of three tests. Continue blows if the two largest are not within 40 L/minute, as the patient is still acquiring the technique.

Interpretation

  • Charts of 'normal values' are available. There are different charts for males and females, as males tend to have higher peak flows than females, all other parameters being equal. Expected PEFR increases with increasing height and it varies with age, reaching a peak in the early 20s and then gradually declining. Current normative charts are criticised for being outdated and not encompassing ethnic diversity.
  • A patient's peak flow can be compared with that listed normal for their age, sex and height. However, it is often more helpful in an asthmatic patient to compare changes with an individual's best peak flow, recorded in a clinically stable period on optimal treatment. Thus, a patient with asthma may have a 'predicted' PEFR of 500 L/minute but know that a peak flow of 400 L/minute indicates reasonable control and that, where it falls to 300 L/minute, appropriate action is required.
  • Patients are frequently asked to record a peak flow diary (recording PEFR several times a day over a couple of weeks). It is normal for peak flow to fall slightly overnight and these 'nocturnal dips' may be accentuated in asthma. A marked diurnal variation in peak flow (>20%) is significant. There may be significant day-to-day variation and the patient may be able to demonstrate that testing PEFR after certain aggravating activities causes measurable dips. PEFR is best recorded on a chart which provides graphical illustration of this variability. Peak flow variability is not specific to asthma and so its diagnostic value is debatable.9
  • Reversibility testing can be performed with PEFR testing in subjects with pre-existing obstruction of the airways and is demonstrated by an increase of >60 L/minute.
  • Peak flow diaries may also be helpful for patients with moderate or severe asthma. They can provide an objective warning of clinical deterioration.

Spirometry

  • Spirometry is now preferred over peak flow measurement for initial confirmation of obstruction of airways in the diagnosis of asthma, as it is felt to offer clearer identification of airway obstruction, to be less effort dependent and more repeatable.9 Spirometry measures the whole volume that may be expelled in one breath (vital capacity). It also permits calculation of the percentage exhaled in the first second (FEV1). However, as with peak flow, some (particularly young children) may not be able to undertake it reliably.
  • Spirometry may be normal in individuals currently asymptomatic and does not exclude asthma and should be repeated, ideally when symptomatic. However, a normal spirogram when symptomatic does make asthma an unlikely diagnosis.
  • It also offers good confirmation of reversibility in subjects with pre-existing obstruction of the airways where a change of >400 mL in FEV1 is found after short-term bronchodilator/longer-term corticosteroid therapy are trialled.

CXR

CXR is remarkably normal, even in very severe asthma. It should not be used routinely in the assessment of asthma but consider CXR in any patient presenting with an atypical history or with atypical findings on examination.9

Diagnosis

Diagnosis in adults

Current guidelines emphasise that the diagnosis of asthma is a clinical one, based on typical symptoms and signs, and a measurement of airflow obstruction for which spirometry is the preferred initial test. Ascribe high, intermediate or low probability of asthma based on this assessment to determine the use of further investigations or treatment trials.9

Clinical features altering the probability of asthma in adults9

Features increasing the probabilityFeatures decreasing the probability
  • Presence of more than one relevant symptom (wheeze, breathlessness, chest tightness and cough), particularly where these are:
    • Worse at night and in the early morning.
    • Triggered by exercise, allergen or cold air.
    • Aspirin or betablocker provoked.
  • A personal or family history of atopy.
  • Widespread wheeze on chest examination.
  • Otherwise unexplained low FEV1 or PEFR.
  • Otherwise unexplained peripheral blood eosinophilia.
  • Prominent dizziness, light-headedness, peripheral tingling.
  • Chronic productive cough without wheeze or breathlessness.
  • Repeatedly normal chest examination when symptomatic.
  • Voice disturbance.
  • Symptoms with colds only.
  • Significant smoking history (>20 pack-years).
  • Cardiac disease.
  • Normal PEFR or spirometry when symptomatic.

Where diagnosis is uncertain (intermediate probability) but with demonstration of airway obstruction ((FEV1)/(FVC) <0.7), reversibility testing and/or a trial of treatment is suggested. Adult patients with normal or near-normal spirometry when symptomatic are likely to have non-pulmonary causes for their symptoms and these should be actively sought.9

Additional investigations of airway obstruction, responsiveness (e.g. histamine or methacholine provocation, exercise or inhaled mannitol challenges) or inflammation (e.g. induced sputum eosinophil count, exhaled nitric acid concentration) may be available through specialists and provide additional diagnostic support in difficult cases but their place in the diagnostic canon remains unclear.9

Diagnosis in children

Diagnosis in children is difficult because of the complex nature of the disorder in the young and is dealt with in the separate article Diagnosing Childhood Asthma in Primary Care. Different 'phenotypes' of wheeze in children are identifiable only in retrospect - episodic viral-induced infant wheeze, some of which may persist/transform into atopic and non-atopic variants of childhood asthma. Also difficulties exist, particularly with younger children obtaining objective evidence of airway obstruction, where they cannot perform peak flow tests or spirometry.

Assessment and review9

See separate article Acute Severe Asthma and Status Asthmaticus.

All patients with asthma in primary care should be reviewed at least annually and reviews should include:

  • Symptomatic control assessment using a directed question-based tool. Even in practices with good resources, there is a great morbidity from inadequately controlled asthma.17The Royal College of Physicians '3 questions' approach has been widely used and valued for its simplicity, although it is poorly validated:
    • Have you had any difficulty sleeping because of your asthma symptoms, including cough?
    • Have you had your usual asthma symptoms during the day (cough, wheeze, chest tightness of breathlessness)?
    • Has your asthma interfered with your usual activities (housework, work, school, etc.)?
    Alternatives include the Asthma Control Questionnaire, Asthma Control Test and Mini Asthma Quality of Life Questionnaire.
  • Measurement and recording of lung function with peak flow or spirometry.
  • Review of exacerbations in the previous year, use of oral corticosteroids and time of school or work.
  • Check inhaler technique.
  • Check patient compliance and bronchodilator reliance. Review medication use - the use of more than 2 cannisters of reliever per month or 10-12 puffs per day is associated with poorly controlled and higher-risk asthma.
  • Check patient ownership and use of an asthma action plan.

Management9

The stepwise approach

See separate articles Management of Adult Asthma and Management of Childhood Asthma. As these are discussed elsewhere, this section will be confined to general principles. The management of asthma is based on 4 principles:

  • Control symptoms, including nocturnal symptoms and those related to exercise.
  • Prevent exacerbations and need for rescue medication.
  • Achieve the best possible lung function (practically FEV1 and/or PEFR >80% predicted or best).
  • Minimise side-effects.

To achieve this:

  • Start at the appropriate step according to the severity of the presenting condition.
  • Achieve early control.
  • Step up or down the medication to enable optimum control without excessive medication. Maintain patients on the lowest possible dose of inhaled steroid. Reduce slowly, with reductions of 25-50%, every 3 months.
  • Always check compliance with current medication, inhaler technique and exclude triggers as far as possible before starting a new drug.
  • Patient education and access to a written personalised action plan are considered critical.

Devices

Delivery of drugs to the lungs is a very efficient method in terms of both swiftness of action and limitation of systemic side-effects. However, it is essential to ascertain that the patient is competent at using the inhaler. Simply giving a prescription for a metered dose inhaler (MDI)is inadequate; steps must be taken to teach the patient to use the device and to check technique. There are many types of inhaler and they can be used by even the very young. The choice is discussed in the separate article Which Device for Asthma The value of spacers is also discussed, as not only the young have poor co-ordination; spacers may be just as important for adults and the elderly who have difficulties. See separate article Nebulisers in General Practice, discussing their use.

Drug treatment

Current UK guidelines advocate the following, stepwise drug management for adults:9

  • Step 1 - for those with very mild, intermittent asthma, the occasional use of a beta2 agonist inhaler may be all that is required but all patients with asthma should be prescribed this for short-term relief of symptoms as required.
  • Step 2 - start regular inhaled steroid at an appropriate dose for the severity of disease (200-800 micrograms/day beclometasone diproprionate or equivalent). Triggers for starting inhaled corticosteroidsshould be:
    • An exacerbation in the previous 2 years.
    • Use of beta2 agonist inhaler more than 3 times per week.
    • Symptomatic of asthma more than 3 times per week.
    • Waking due to asthma more than once per week.
  • Step 3 - initial add-on therapy involves the addition of a long-acting beta2 agonist (LABA). These should not be used without the concurrent use of inhaled steroid. Where control is good, continue but where there is no response, stop and increase the dose of inhaled corticosteroid (up to 800 micrograms/day beclometasone diproprionate or equivalent). With partial benefit, continue the LABA but also increase the inhaled corticosteroid dose. If this fails to provide control, trial a leukotriene receptor antagonist or sustained release (SR) theophylline.
  • Step 4 - with persistent poor control, increase inhaled steroid up to 2,000 micrograms/day beclometasone diproprionate or equivalent and/or add a fourth drug (leukotriene receptor antagonist, SR theophylline or beta2 agonist tablet).
  • Step 5 - continuous or frequent use of oral steroids, maintaining high-dose inhaled steroids.

Referral to a respiratory physician would be normal at step 4-5 depending on expertise.

Exercise-induced asthma

For most, exercise-induced asthma indicates poorly controlled asthma and will require regular inhaled steroid treatment beyond the anticipatory use of a bronchodilator when preparing for sport. Where exercise poses a particular problem and patients are already on inhaled corticosteroids, consider the addition of long-acting beta agonists, leukotriene inhibitors, chromones, oral beta2 agonists or theophyllines.

Complications

Inadequate control of asthma leads to much morbidity and poor quality of life. 12.7 million working days per year are lost to asthma in the UK and there were 77,000 asthma-related emergency admissions in 2005.3
Complications mostly relate to acute exacerbations:

  • Pneumonia
  • Pneumothorax
  • Pneumomediastinum
  • Respiratory failure and arrest
  • Death

Individuals continue to die from asthma (approximately 1,300 deaths in the UK from asthma in 20053). A common feature of deaths from asthma is that the patient and/or the medical staff have underestimated the severity of the attack. Patients frequently have adverse psychosocial factors that interact with the ability to judge or manage their disease, leading to late presentation. A confidential enquiry from the east of England concluded that in two-thirds of asthma deaths, medical management failed to comply with national guidelines. It is suggested that 'at-risk' asthma registers in primary care may improve recognition and management of high-risk patients.18,19

Prognosis

Many children will wheeze early in life (about 30% of those aged under 320) in response to respiratory tract infections but most appear to grow out of it by the time they go to school. A few will continue to wheeze and develop persistent or interval symptoms, similar to older children with atopic asthma. Predictors for continued wheezing include:9

  • Presentation after the age of 2 years.
  • Male sex in prepubertal children.
  • Frequent or severe episodes of wheezing.
  • Personal or family history of atopy.
  • Abnormal lung function.

Some children present with asthma later in childhood and they appear to be less likely to have markers of atopy early in life compared with the persistent early wheezers.21

Prevention

In order to determine effective primary prevention strategies, we need to unpick the epidemiology of asthma, clearly identify risk and protective factors and come closer to an understanding of asthma's aetiology and changes in prevalence figures. It is striking how little we fully understand about what causes asthma. Whilst family history remains the strongest risk factor for developing atopic asthma, the interplay of the environment is far from clear. The 'hygiene hypothesis' is currently popular. It suggests that decreased exposure to childhood infections, endotoxin and bacteria increases the risk of developing atopy.22 Current guidelines suggest the promotion of breast-feeding (for its other benefits and possible preventative effect) and smoking cessation amongst parents, but evidence for other strategies (e.g.modifying maternal diet during pregnancy, weaning strategies or early aeroallergen avoidance) is lacking.9


Document references

  1. Fireman P; Understanding asthma pathophysiology. Allergy Asthma Proc. 2003 Mar-Apr;24(2):79-83. [abstract]
  2. British Medical Association; Quality and Outcome Framework 2008: summary of indicators (clinical domain)
  3. The Asthma Divide, Asthma UK
  4. Anderson HR, Gupta R, Strachan DP, et al; 50 years of asthma: UK trends from 1955 to 2004. Thorax. 2007 Jan;62(1):85-90. [abstract]
  5. Asthma: statistical information, Lung and Asthma Information Agency; Website for lay people but well presented
  6. Hunninghake GM, Cho MH, Tesfaigzi Y, et al; MMP12, lung function, and COPD in high-risk populations. N Engl J Med. 2009 Dec 31;361(27):2599-608. Epub 2009 Dec 16. [abstract]
  7. Weiss ST; What genes tell us about the pathogenesis of asthma and chronic obstructive Am J Respir Crit Care Med. 2010 Jun 1;181(11):1170-3. Epub 2010 Feb 4. [abstract]
  8. Cates C; Chronic asthma. BMJ. 2001 Oct 27;323(7319):976-9.
  9. British Guideline on the Management of Asthma, British Thoracic Society (BTS) and Scottish Intercollegiate Guidelines Network (SIGN), 2009
  10. Chinn S, Downs SH, Anto JM, et al; Incidence of asthma and net change in symptoms in relation to changes in obesity. Eur Respir J. 2006 Jul 26. [abstract]
  11. Frank P, Morris J, Hazell M, et al; Smoking, respiratory symptoms and likely asthma in young people: evidence from postal questionnaire surveys in the Wythenshawe Community Asthma Project (WYCAP). BMC Pulm Med. 2006 May 22;6:10. [abstract]
  12. Thomas M, Custovic A, Woodcock A, et al; Atopic wheezing and early life antibiotic exposure: a nested case-control study. Pediatr Allergy Immunol. 2006 May;17(3):184-8. [abstract]
  13. Akobeng AK, Heller RF; Assessing the population impact of low rates of breast- feeding on asthma, coeliac disease and obesity: the use of a new statistical method. Arch Dis Child. 2006 Jul 13. [abstract]
  14. Riedler J, Braun-Fahrlander C, Eder W, et al; Exposure to farming in early life and development of asthma and allergy: a cross-sectional survey. Lancet. 2001 Oct 6;358(9288):1129-33. [abstract]
  15. Gray RD, Duncan A, Noble D, et al; Sputum trace metals are biomarkers of inflammatory and suppurative lung disease. Chest. 2010 Mar;137(3):635-41. Epub 2009 Oct 3. [abstract]
  16. Vaswani R, Moy R, Vaswani SK; Evaluation of factors affecting peak expiratory flow in healthy adults: is it necessary to stand up? J Asthma. 2005 Nov;42(9):793-4. [abstract]
  17. Jones KP, Bain DJ, Middleton M, et al; Correlates of asthma morbidity in primary care. BMJ. 1992 Feb 8;304(6823):361-4. [abstract]
  18. Harrison B, Stephenson P, Mohan G, et al; An ongoing Confidential Enquiry into asthma deaths in the Eastern Region of the UK, 2001-2003. Prim Care Respir J. 2005 Dec;14(6):303-13. Epub 2005 Oct 11. [abstract]
  19. Noble MJ, Smith JR, Windley J; A controlled retrospective pilot study of an 'at-risk asthma register' in primary care. Prim Care Respir J. 2006 Apr;15(2):116-24. Epub 2006 Feb 28. [abstract]
  20. Piippo-Savolainen E, Korppi M; Wheezy babies--wheezy adults? Review on long-term outcome until adulthood after early childhood wheezing. Acta Paediatr. 2008 Jan;97(1):5-11. Epub 2007 Dec 3. [abstract]
  21. Matricardi PM, Illi S, Gruber C, et al; Wheezing in childhood: Incidence, longitudinal patterns and factors predicting persistence. Eur Respir J. 2008 May 14;. [abstract]
  22. Liu AH; Hygiene theory and allergy and asthma prevention. Paediatr Perinat Epidemiol. 2007 Nov;21 Suppl 3:2-7. [abstract]

Internet and further reading

Acknowledgements

EMIS is grateful to Dr Gurvinder Rull for writing this article and to Dr Chloe Borton for earlier versions. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2010.
Document ID: 2055
Document Version: 26
Document Reference: bgp620
Last Updated: 12 Oct 2010
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