Asthma is a growing health problem affecting adults and children across the world. The symptoms associated with the disease can be triggered by a number of stimuli, not least the weather. By combining the expertise of the Met Office with that of health experts, we are now working towards predicting weather-sensitive asthma outbreaks.

A chronic condition

Asthma is not a trivial disease; at least 2,000 people die from it each year in the UK. It is estimated that the condition affects 10-15% of people and appears to be getting more common. In fact, recent figures suggest that there has been a 1.7 million increase in the number of people with asthma within the last decade.

Asthma attacks are known to have a seasonal pattern, and it is now widely recognised that thunderstorms have a strong link with asthma admissions. To help GPs and hospitals cope with the extra workload caused by asthma outbreaks associated with the onset of thunderstorms, the Met Office is working with Dr Shuaib Nasser (Chest consultant at Addenbrookes Hospital, Cambridge) to help explain and accurately predict these 'asthma storms'.

A major outbreak

In 1994 there was a major outbreak of thunderstorm-associated asthma, when a large thunderstorm crossed London, causing over 1,000 attendances at Accident and Emergency (A&E) departments. The combination of a previous dry spell, which allows pollen to be sucked into the storm and then deposited in a concentrated area - causing very localised, high levels of pollen - appears to be the cause of these asthma outbreaks. The addition of high ozone levels may increase the sensitivity of the lungs, resulting in more-severe symptoms

Summer 2002

The summer of 2002 was generally wet, with much thundery activity leading to some severe flooding. These storms led to a notable asthma outbreak in eastern England on the night of 30 July. It had been a very hot day and the previous week had been dry and warm. Unusually for that late in the season, grass pollen levels were still high. A series of mesoscale storms - known to be associated with asthma outbreaks - had also moved up from London and Essex. The final ingredient was the very high ozone level, which peaked during that day.

As the storm moved north, it sucked up pollen and forced it up to the tops of the towering thunderclouds. This process shattered the pollen into smaller pieces, making them even more allergenic. When the rain began to fall, young people with a history of hay fever, but not necessarily asthma, started to develop chest tightness.

It is estimated that more than 100 people attended A&E departments throughout the area that night; some were seriously ill and had to be admitted.

Environmental factors

These incidences demonstrate that the weather can have a profound impact on asthma, although further investigation is necessary. The increase in the prevalence of asthma over the past few decades has also been linked to environmental factors, such as air pollution, exposure to chemicals and tobacco smoke, viral infections and socio-economic disadvantages.

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