Management – Allergen avoidance II

Pollen

Allergy to airborne pollen grains from certain grasses, weeds and trees:

is common in people with asthma
may worsen asthma symptoms during the pollen seasons (usually in spring, early summer or during the dry season in tropical regions)
can cause outbreaks of asthma attacks after thunderstorms⁹⁵
is usually caused by imported grasses, weeds and trees, which are wind pollinated – the pollen can travel many kilometres from its source
is not usually caused by Australian native plants (although there are exceptions, such as Cypress Pine)
is not usually caused by highly flowered plants as they produce less pollen (which is transported by bees) than wind pollinated plants.

Pollen avoidance measures

The following measures may help reduce exposure to pollen, but are yet to be proven to improve asthma control:

Remain indoors on windy days or after thunderstorms.
Avoid activities known to cause allergen exposure – such as mowing grass.
Shower after outdoor activities where exposure to pollen is high.
Use recirculated air in the car when pollen levels are high.

Forecasting of relevant grass, weed and tree pollen counts may be of use to people with asthma with known pollen sensitivities. In the USA where pollen counts are routinely quoted on weather forecasts, their clinical utility has not yet been tested.

Cockroach

Cockroach allergen may be relevant in the warmer climates in Australia. Studies from other countries suggest that children allergic to and exposed to the cockroach allergen in dust have increased risk of:

hospitalisations and emergency presentations with asthma
more symptoms of persistent asthma.^{25
<LEIII-2>}

Measures that reduce sites for breeding and remove cockroaches and the allergen they produce may help reduce exposure.⁹⁶ However as yet this is unproven.

Mould

Like other environmental allergens, indoor exposure to mould has been shown to correlate with wheezing and peak flow variability.^{97-100
<LE IV>}

Fungal exposure occurs both indoors and outdoors. Exposure to moulds such as Alternaria increases the risk of asthma symptoms and airway reactivity in sensitised children and the risk of sudden respiratory arrest in sensitised young adults with asthma.^{29,
101 <LE III-2>}

Mould avoidance measures

Dehumidifiers in the home do not provide any benefit for asthma control.^{79
<LE III-1>}

Air filters and ionizers have been shown to reduce airborne mould, however a direct effect on asthma control has not yet been shown.⁷⁹

Other avoidance measures which have not been adequately tested include:

application of fungicides such as bleach with detergent or quaternary amine preparations
removal of indoor plants
using high-efficiency air filters
natural ventilation of homes
removal of garden mulch and compost.

Food

Foods are not common triggers for asthma.

Many people with asthma believe that food often induces symptoms. However:

as few as 2.5% of people with asthma actually react to the food in blinded challenges¹⁰², whereas 20-60% of people with asthma feel that food may be a trigger factor^103-105
allergy to foods such as nuts, fish, shellfish, milk and eggs may trigger asthma symptoms in conjunction with other symptoms in the skin or gut, as part of an anaphylactic reaction. However this is uncommon in children with asthma (5.7-8.5%) and rare in adults (2%). Such reactions usually occur within minutes of ingestion^{106,
107}
foods rarely cause respiratory symptoms alone, without other symptoms in the gut or skin.^{108,
109}

A careful history of each episode needs to be taken. Suspected food/s can be further investigated using skin prick tests or RAST tests. If these are negative, it is unlikely that the food has triggered the asthma symptoms.

Food additives

The role of food additives in asthma is controversial.

Sulphites such as sodium metabisulphite, can trigger asthma symptoms in susceptible individuals with pre-existing asthma.^{110
<LE II>} They are found in processed foods, dried fruit and beverages (eg beer and wine).
There is little evidence that food colours (eg Tartrazine) and preservatives can provoke asthma.^{111,
112}
Monosodium glutamate (MSG) has not been shown to provoke asthma in double blind placebo controlled (DBPC) trials.^113-115 This is in contrast with earlier reports of associations of these additives and asthma.¹¹⁶ If MSG does cause asthmatic reactions this is rare.

There is no validated test for adverse reactions to chemicals and food additives, as most of these reactions are not IgE mediated and hence cannot be tested for using skin prick or RAST tests. A challenge is needed to make a definitive diagnosis.¹¹⁷ This must be performed in an appropriate centre with access to resuscitation facilities. A referral to an allergy specialist is required.

Double blind placebo controlled challenges (DBPCC) remain the gold standard. These are usually not available outside research centres. Single blind placebo controlled challenges (SBPCC) are usually used in clinical practice.

Any suspicion about the role of foods and food additives in triggering asthma should be assessed by an allergy specialist. If foods are confirmed as asthma triggers, allergy specialists may recommend a dietitian for advice.