David Skegg: Screening programme triumph of preventive medicine

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At public hearings during 1987 and 1988, the medical profession was turned on its head by revelations about the treatment of women with cervical abnormalities at National Women's Hospital. The Cartwright Inquiry had profound effects on the delivery of healthcare in this country.

While many of the changes were necessary and overdue, others might be regretted.

So it is inevitable that events surrounding this inquiry will be reviewed and debated.

Sadly Linda Bryder's new book, A History of the 'Unfortunate Experiment' at National Women's Hospital, will produce confusion rather than clarity.

A social historian can hardly be blamed for misunderstanding scientific evidence, but her book's factual errors and selective quotations make it seem more like an exercise in polemic than academic scholarship.

Dr Herbert Green was a strident opponent of cervical screening, even after it had been shown to be beneficial. Given Professor Bryder's eagerness to defend all of Green's positions, it was unsurprising that Kim Hill (on Radio NZ) kept asking her a question about our national cervical screening programme: "Is there any evidence that it is actually saving lives?" This is an important question which can be answered squarely.

The achievements of the national screening programme, which was a direct outcome of the Cartwright Inquiry, have exceeded expectations.

Despite many trials and tribulations in getting the scheme established, it has turned out to be a triumph of preventive medicine.

Cervical cancer is now known to be caused by certain types of human papillomavirus (HPV) which are transmitted sexually.

A woman's risk depends not only on her own behaviour, but on the pattern of sexual behaviour in society as a whole.

HPV infections are surprisingly common, but they are usually transient. Several factors are believed to increase the risk an HPV infection will persist and progress to cause cervical cancer. These include cigarette smoking and long-term use of oral contraceptives.

The sexual revolution which started in the 1960s led to an increase in reproductive tract infections, as men and women tended to have more sexual partners. Many young women took up smoking, and the pill became a popular method of contraception.

All of these changes would be expected to increase the incidence of cervical cancer, and that's what happened among young women in New Zealand as well as in several other countries.

Green was actually the first to report the rising incidence and death rate in New Zealand - trends which he described as alarming. He took these trends as evidence that cervical screening was ineffective, overlooking the fact that a rising incidence was to be expected for other reasons.

Subsequent research by Dr Brian Cox suggested that even the unsystematic screening in the 1970s was preventing about a quarter of invasive cancers. It was helping to keep an emerging epidemic in check.

Observations in other countries had shown that generations of women who experience increased rates of cervical cancer at young ages continue to experience high rates throughout their lives. Epidemiologists call this a birth-cohort effect.

Brian Cox and I reported analyses of the trends in 1986. A mathematical model showed the numbers of women developing, and dying from, cervical cancer would increase strikingly unless effective control measures were introduced.

Later we published projections of the likely burden of cervical cancer over the next two decades, estimating what might be achieved by plausible improvements in screening.

Those two decades have now passed, so it is instructive to see what has actually happened. Our model predicted that by 2004 the annual number of new cases of cervical cancer would have nearly doubled from 235 to 442, while the number of deaths would have increased from 101 to 148 per year.

Those projections were conservative, because we assumed that the female population would expand to only 84 per cent of what eventuated. Far from doubling, the annual number of new cases fell from 235 to 157 (in 2004-07), while the number of deaths declined from 101 to 59 per year (in 2004-06).

We had shown that any trend towards safer sexual behaviour could produce only minor effects over this period, and the reduction due to screening was far bigger than we expected.

Taking account of the actual increase in population, we can calculate that screening is now preventing at least 70 per cent of the cases of cervical cancer that would otherwise be occurring in New Zealand.

Regular screening will need to be continued to maintain the gains made. More could be achieved by improving the coverage of groups at high risk (such as Maori women), but already more than 100 deaths every year are being prevented. Many of the women whose lives are being saved would have died in middle age, often with young children in their care.

The success in implementing organised cervical screening reflects the dedication of many people, including health professionals and women's groups.

A concerted national effort was needed, and this would not have occurred without the shock of the Cartwright Inquiry.

If only we could muster similar determination to tackle other public health challenges, such as our lamentable failure to control rheumatic fever in children.

* Sir David Skegg is the Vice-Chancellor of the University of Otago. He is an adviser to the World Health Organisation on reproductive health and research.