F.J. van Ittersum and L.J.M. Hendriks

1.5.1 Preventive diagnostics and preventive treatment

1.5.1.1 Shift from emphasis on therapeutic to preventive medicine in the 20th century

In the second half of the 20th century, the focus in medicine shifted more towards prevention and early detection of diseases, even though much of the attention of doctors and nurses is still on curing diseases or conditions and alleviating their symptoms. Examples of disease prevention include taking hygienic measures to prevent the spread of infectious diseases, vaccinations to drastically reduce the irreversible complications of infectious diseases in particular, treatment of mildly elevated blood glucose levels, mildly elevated blood pressure levels or cholesterol levels to reduce the development of cardiovascular disease in the long term. Giving lifestyle advice such as quitting smoking or limiting alcohol consumption also falls under preventive medicine. Examples of early disease detection in the Netherlands are, first of all, the ongoing population screening programmes: cervical carcinoma (cervical cancer), mammary carcinoma (breast cancer) and colon carcinoma (colorectal cancer). In addition, there are specific risk groups that are screened for the presence of certain conditions, especially people with relatives with genetically determined conditions.

Those who undergo preventive screening or receive preventive lifestyle advice or treatment almost never have symptoms of the condition that prevention is targeting, but are hopefully either treated at an earlier stage, increasing their chances of being cured, or are saved from permanent disease symptoms or physical or mental disabilities in the future.

Although difficult to prove, it is plausible that the aforementioned forms of preventive medicine in the 20th century contributed significantly to the increase in life expectancy that occurred during that period. The decline in tuberculosis cases is mainly due to improved hygiene and living conditions and not to the introduction of tuberculostatics, antibiotics that can be used to fight the Mycobacterium tuberculosis bacilli; the decline in Cardiovascular Accidents (CVAs, strokes) is partly due to better treatment of asymptomatic hypertension. Also, much can be expected from the decline in smoking rates on the number of people who develop Chronic Obstructive Pulmonary Disease (COPD, formerly emphysema) or lung cancer. Because these diseases can still occur many years after smoking cessation, the maximum benefit of this has yet to be achieved.

In prevention, not all examined (screened) or treated individuals achieve gains from preventive measures or treatments. Not every woman who has a smear test ever gets a cervical carcinoma, not everyone with long-term hypertension gets a CVA. Thus, a certain number of people will need to be screened or treated in order to diagnose disease in one person or, in the case of treatment, prevent a complication. In epidemiology, these numbers are known as Number Needed to Screen (NNS) and Number Needed to Treat (NNT). For example, to prevent one case of cervical carcinoma, 2560 women had to have a smear taken in the year 2000: the NNS is then 2560. If over 5 years 100 people need to be treated for hypertension to prevent one CVA, the NNT over 5 years is 100.

NNS and NNT thus say something about the effectiveness of screening and preventive treatment, respectively, and thus something about the costs. In the case of an NNS or NNT of 20, the costs of screening or preventive treatment in relation to the one case detected or prevented are much lower than if the NNS or NNT had been 1000. Of course, the costs still depend on the price of one screening test or one preventive treatment. It is the cost of laboratory or X-ray tests or the cost of using blood pressure-lowering drugs over the number of years of the NNT.

NNS and NNT together with the cost of screening or treatment of a single person determine the financial burden that a prevention programme places on society.