This year, fewer than 50,000 appendices will be removed. So what has happened? Were surgeons in the 1960s taking out thousands of healthy appendices or is appendicitis destined to become a relic of medical history?
The experts say the incidence of appendicitis is genuinely falling. True, surgeons are less scalpel-happy - only about 15 per cent of appendices removed today are healthy compared to about 25 per cent 20 years ago - but this does not fully explain the decline.
At first, epidemiologists thought the fall must be the result of a healthier diet, but studies proved negative. 'We can now definitively say that the fall is not due to dietary fibre,' says Dr Richard Logan, senior lecturer in medicine at the University of Nottingham.
The latest theory is that the fall is linked to the incidence of intestinal infections. If a child gets a bug, the lymph glands around the appendix swell up and the appendix becomes inflamed. Since hygiene has improved and gut infections have become rarer, appendicitis has declined. However, this is still just a theory.
Appendicitis is not the only disorder mysteriously declining in Britain. Others affecting the digestive system, including gastric and duodenal ulcers and stomach cancer, are also on the wane. And so are the big killers: heart disease and stroke.
Scientists are fascinated by the fall, believing that if they discover the precipitating mechanisms, they will find the diseases' underlying causes. But pinpointing the causative factors is far from simple. Trends in disease may mirror trends in behaviour, but be unrelated. Scientists have produced graphs showing that the rise in lung cancer in the 1950s perfectly matched the rise in ownership of television sets. Does that mean TV causes cancer?
When Sir Richard Doll, emeritus professor of medicine at Oxford University, investigated the cause of the rise in lung cancer, he started by assuming it was because of the increase in petrol fumes as cars became more common. It was only through meticulous detective work that the role of cigarettes was discovered.
Now similar detective work is being carried out to discover why some diseases are declining. Scientists believe that the fall in peptic ulcers is a result of the mysterious drop in the prevalence of a stomach bacterium, Helicobacter pylorum. Almost 70,000 patients were admitted to hospital with peptic ulcers in 1957; today the number is closer to 20,000.
'We used to think ulcers were more common among executives,' says Professor John Alexander-Williams of Birmingham University. 'But we now think that was just because middle-class people made more of a fuss.' While the fall in smoking has definitely contributed to the decline, and changes in diet may have done, doctors now believe that the role of Helicobacter pylorum is crucial. 'We know that people catch the bacterium in their teens or earlier, and that no single drug can get rid of it,' says Dr Robert Walt, senior lecturer in medicine at Birmingham University. The bug remains in the stomach all through life and makes an ulcer more likely in middle age. But the bug is much less common among younger people than it used to be, possibly because living standards have improved. Its decline may also account for the fall in stomach cancer.
Fierce debate surrounds the rise in coronary heart disease, which started at the beginning of the century, and the fall, which began in Britain in the late 1970s. Deaths have fallen, from 160,000 in 1978 to 145,000 in 1992.
Conventional wisdom has it that changes in life style - particularly giving up smoking and switching from saturated to unsaturated fats - have caused the continuing drop. But a team of scientists at Southampton University, led by Professor David Barker, believes that whether or not someone will develop heart disease is decided in the womb.
Professor Barker and his team have traced the health records of thousands of men and women born in Hertfordshire between 1911 and 1930 and found that those who were lighter than average at birth, and at the age of one, had a greatly increased risk of dying prematurely from heart disease. 'I am not saying that smoking, obesity and exposure to saturated fat in adult life do not matter. But the significance of these things may have been overestimated,' Professor Barker says. 'The importance of foetal development has been overlooked.'
If a foetus is not adequately nourished late in pregnancy the liver does not develop properly so that cholesterol in the diet is not fully broken down, resulting in high blood cholesterol levels in adulthood. Barker thinks the rise in heart disease was a result of increasing affluence in the early part of the 20th century and people's high-fat diet. The fall resulted from better maternal nutrition, which enabled the next generation to deal better with such a diet.
His theories are 'interesting', according to Professor Michael Marmot of University College and Middlesex School of Medicine, London, but they do not explain, for example, the United States' experience.
Heart disease started to decline in the US in all age groups at the same time, not just among those whose mothers benefited from better nutrition. 'You have to look at what changed in the 1970s. There was a marked decline in smoking both in the US and in Britain, so that is one candidate,' Marmot says. 'The other thing that changed was our diet. There was no decline in total fat intake in the UK, but there was a change in the type of fat. We began to eat more polyunsaturated fat around 1975 onwards. When these changes occurred, heart disease started to decline. It would be a cruel joke if the two were not linked.'
Doctors believe that the decline in strokes - deaths fell from 80,000 in 1971 to 66,000 in 1992 - may be attributed to a combination of factors: better control of blood pressure, lower blood cholesterol levels, less smoking and a lower intake of salt. But they acknowledge that a great deal more work needs to be done.
Might we look back on gut disease, heart disease and stroke in the 21st century in the way we look back on the Black Death of the 14th? Dr Malcolm Law, senior lecturer at the Wolfson Institute of Preventive Medicine at St Bartholomew's Hospital, says: 'We still have a long way to go before we can say that stroke and heart disease are disappearing. But at least they are going in the right direction.'-
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