The weather affects patterns of sickness, so predicting it can help the health service plan for outbreaks of flu and other illnesses. Lynn Eaton reports

With one eye on a general election, prime minister Tony Blair has a secret weapon up his sleeve to help with the winter pressures on the NHS: the Met Office.

In an unlikely partnership, the weathermen and women are offering a unique service to five pilot areas, predicting not only the weather, but the likely outbreaks of respiratory illness, heart attack, stroke - and even flu.

The Met Office's alarming prediction is that, although Britain has so far escaped a flu epidemic, it will probably hit over the next two weeks.

Dr William Bird, a GP from Oxford with a keen interest in how the weather affects illness patterns, joined the Met project late last year.His team includes an epidemiologist, climatologist, statistician, meteorologist, airquality consultant and data manipulation specialist.

'When we looked at the weather over the past 30 years, we saw there was a sudden increase in heart attacks three days after a cold spell, in strokes five days later and in respiratory diseases 12 days later, ' says Dr Bird. 'It seems to be when there is a significant drop below the average temperature - anything of 5degrees or more - rather than when it hits a specific temperature.'Dr Bird says the optimum temperature for a healthy nation is 18degreesC. For every degree the temperature drops, mortality rates increase 1.5 per cent.

'That is by far the highest in Europe, mainly because we do not dress ourselves appropriately when it gets cold, ' he says.

Flu is not so specifically linked to temperature drops, but can occur when cold weather is followed by a prolonged spell of a 'low-boundary layer' of air - mist and murk that do not clear.

'Just before the 1989 flu epidemic there was an abnormally prolonged low-boundary layer, ' says Dr Bird. Germs are trapped in the air, unable to escape, so the chance of infection is higher. Dr Bird predicts that this will happen soon and, as there is already flu on the continent, both factors combined will make a flu outbreak in the UK more or less inevitable.

The team is examining hospital episode statistics data for cardiac, stroke, respiratory disease and hip fractures for all NHS admissions in England over the past 10 years. It will then map these against the weather to determine any pattern. It is also collecting up-to-date daily data from hospitals and GP co-ops in five pilot areas. These are: Leeds General Infirmary and Leeds cooperative; Derriford Hospital in Plymouth and Devon Dock cooperative; the Royal Berkshire Hospital in Reading and Reddoc;

North Middlesex Hospital in London and Harmoni cooperative; and New Cross Hospital in Wolverhampton and Wolverhampton co-operative.

Hospitals provide daily returns of acute medical admissions; the co-operatives supply figures for patients seen or given telephone advice for all complaints. NHS Direct is also providing figures for respiratory-related calls.

The snowfall after Christmas was predicted on the general weather forecast, but Dr Bird's tailor-made prediction for the NHS advised that the pressure on accident and emergency wards would come not on the first day of the snow, but three days later.

'The third day is when casualties come in, when the snow has melted and re-frozen. Old ladies are running out of milk and eggs, so they go out then, when they wouldn't have gone out on the first day it snowed. There are also fewer hip fractures on Sunday than on other day. It must be that elderly people do not shop then.'

Also, his predictions can be tailored to a specific area, rather than the general forecast.

Heather Bunce, clinical services unit manager at the Royal Berkshire Hospital, has already noticed the difference. 'The Thursday morning before Christmas they were saying we would reach a peak in cardiac cases following a cold spell the week before. I was cardiac manager at the time and by 8pm it was happening. It was spooky.

'If we match what the Met Office is giving us with our capacity model designed by Southampton University, it appears we can predict what will happen. Last Tuesday it looked as if influenza was on its way, so I've told staff to batten down the hatches.'

It is early days, so Ms Bunce is reluctant to rely entirely on the Met Office predictions just yet.

'We are using it with very well developed capacity plans. I am not sure I am confident to use it blind at the moment, ' she says.