Types of prevention

Primary and secondary prevention

Prevention may be classified as primary or secondary:

• Primary prevention is aimed at healthy individuals to prevent disease from occurring. Examples include:
  • Vaccinations
  • Wearing of seatbelts
  • Adopting a healthy lifestyle. For example:
    • Diet
    • Weight
    • Exercise
    • Avoidance of smoking
    • Avoidance of excess alcohol
    • Practising safe sex
    • Avoidance of drug abuse
• Secondary prevention is aimed at patients with an existing pathology to reduce the risk of recurrence or progression. For example:
  • Aspirin in arterial disease.
  • Beta blockers and ACE inhibitors after myocardial infarction.
  • Smoking cessation in Chronic Obstructive Pulmonary Disease (COPD) and established arterial disease.
• Many interventions may be either primary or secondary, depending upon the circumstances. For example:
  • Smoking cessation in ischaemic heart disease and COPD.
  • Statins may be used in both primary and secondary prevention.

The numbers needed to treat (NNT) and show benefit in at-risk populations (as in secondary prevention) are smaller. However the aim of preventing disease occurring at all is an appealing one.
Preventive measures applied to high risk groups in secondary prevention are often inappropriate for primary prevention. An example is the use of aspirin for CHD (figures used for illustration only). Suppose that the number needed to treat to prevent 1 myocardial infarction (giving say 75 mg daily for 5 years) was 100 for secondary prevention. Suppose that the NNT is 10,000 for primary prevention (in a low risk group). Suppose also that the risk of adverse effects such as gastro-intestinal haemorrhage is such that the number needed to harm (NNH) is 1 in 1,000 in both groups. In the high risk group the NNT is 100 and the NNH is 1,000. Therefore the intervention may be justified. In the low risk group, the NNT is 10,000 and the NNH is 1,000, so the intervention is not justified. Also a high NNT means greater expense per positive outcome. This helps explain why the accepted wisdom is that aspirin is effective in high risk groups^[1] but is not recommended for the community as a whole.

Levels of prevention

Prevention is also classified according to the level at which action is taken. Thus it can be at the national, local or personal level.

• At the national level, interventions include legislation such as compulsory seatbelts or motor cycle crash helmets. Taxation can influence activity.^[2] In other countries it may involve the eradication of mosquitoes or the provision of clean drinking water and sewage disposal. In the UK only 5% of water supplies are fluorinated.^[3] This is discussed further in some dental and periodontal problems. Governments may also initiate education campaigns.
• At the local level, the provision of cycle paths and sports centres facilitates exercise, and healthy eating should be an easy option in canteens in schools and places of work.
• At work, health and safety is overseen by the Health and Safety Executive. They are a helpful organisation who prefer to facilitate but where regulations are breached they have powers to act as well.
• At the personal level individuals make personal decisions about lifestyle. Individuals consulting with health professionals may be advised about diseases, treatments and personal management of preventive health measures.

Wherever possible, doctors as individuals and as a profession should encourage national government, local government or other organisations in measures to prevent disease and to promote health. However the majority of interventions by most health professionals will be at the personal level with the individual patient. Public health doctors work more often at other levels with opportunities to advise and influence local and national government. On a personal level doctors are well placed to set an example by following a healthy lifestyle.

The challenges of prevention

Political challenges

The scope for the prevention of diseases is enormous. There will be scope for prevention of all types and at all levels and much of this will require political change. Many people in the developed world are dying from diseases of 'excess'. For example those related to smoking and obesity. In large parts of the world malnutrition and infectious diseases kill millions, often at a young age. AIDS has caused devastation throughout much of sub-Sahara Africa and other parts of the world. Smoking-related diseases are increasing in developing countries where tobacco companies have been promoting sales. Widespread disease and death still occurs in many countries around the world without a clean and plentiful water supply. Wars and armed conflict have hindered or destroyed the development of basic infrastructure in many parts of the world. Worldwide it is evident that measures at government level will yield the greatest gains.

Specific challenges

Many of these are clinical or individual challenges. Almost every article about a disease, on the EMIS Mentor system, has a concluding paragraph about prevention of that disease. This may include the barriers to prevention. Articles of particular note include:

• Accidents and their Prevention: discusses the prevention of many types of accident.
• Diving Accidents: highlights prevention.
• Antenatal Care: is preventative medicine.
• Gunshot Injuries: examines laws concerning firearms' licensing in different countries.
• Prevention of Falls in the Elderly: is self-explanatory.
• Stroke Prevention.
• Health and social class: examines uptake of a healthy lifestyle.
• AIDS Acquired Immune Deficiency Syndrome: contains much about prevention and barriers to prevention.
• Obesity in Adults: discusses prevention and barriers to prevention.
• Physical Training: examines the benefits of activity and how to advise about appropriate training.
• Sexually Transmitted Disease (STD): examines transmission. There are articles on the primary prevention of cardiovascular disease and helping patients with smoking cessation.
• Childhood Immunisation Schedule (UK) and other vaccinations.
• On a global scale, Hepatitis B Vaccination and Hepatitis B Prevention is prevention of hepatocellular carcinoma.
• Cervical Screening (Cervical Smear Test): reviews the benefits of this preventive health programme.

Screening for disease

There are a number of criteria that must be fulfilled for a screening procedure to be viable. These were outlined by Wilson in 1966.^[4] Cervical cytology and breast screening^[5] both match these criteria quite well.

• The disease must be sufficiently common within the group to be screened that a reasonable number of cases can be expected to be detected.
• There is benefit in early detection. This may mean offering treatment at a more favourable stage or taking action to prevent or ameliorate the disease. There is no point in detecting pathology if there is nothing that can be done about it.
• The screening procedure must be cheap, easy and acceptable. The last is a problem with regard to faecal occult blood for colorectal carcinoma or prostatic biopsy for carcinoma of prostate. It is also a problem for cervical cytology amongst some ethnic groups.
• The screening test is not usually the gold standard for diagnosis and so there must be an acceptably small number of false positive results. Low specificity will overload the system with further investigation and lead to unnecessary anxiety.
• There must be a very low level of false negatives. Low sensitivity with too many false reassurances will bring the test into disrepute.

The problem with sensitivity and specificity is that there may be some overlap between normal and abnormal results. If the arbitrary line to divide the two is set too far in one direction, there will be too many false positives and if it is set too far the other way there will be too many false negatives. It is important that the public should realise that a screening test is not infallible and that false positives will occur and also some false negatives. When mammography detects 94% of tumours in the group screened, we should applaud the 94% detected and so treated earlier. Bewailing the 6% missed may undermine a very effective system.

Screening for prostate cancer is a problem.^[6] Estimation of PSA is insufficiently discriminative, whilst transrectal ultrasound may have difficulties with uptake, and many detectable malignancies would not advance to clinical significance in the patient's lifetime. Hence it would not benefit the individual.

A database containing family histories allows screening for hypertension and hypercholesterolaemia in those with close relatives with heart disease. Early mammography may be appropriate in women with a mother, aunt or sister with breast cancer before 50 years of age.^[7]

Integrating prevention in the consultation

There is now politically and professionally an expectation of a preventive component to every general practice consultation.

• Professionally seminal works such as The doctor, the patient and his illness,^[8] as well as Doctors talking to patients^[9] and Consultation analysis^[10] considered the issue of health promotion within the consultation.
• Politically financial incentives have been used to influence behaviour and are now used routinely under the existing GP contract which allows for review of targets and incentives.

This still poses a challenge when consultation time is limited and patients come with their own aims and expectations.

Targets for prevention

Some primary prevention is relevant to all of us. For example advice on diet and exercise^[11] may be applicable to everyone. However most measures need to be targeted so that they can be cost-effective and clinically appropriate. Giving statins to everybody over 21 years of age might eventually prevent death from strokes and ischaemic heart disease but it would be prohibitively expensive. The adverse events might also exceed the benefits. Giving statins to those with CHD is cost-effective and is now standard practice. Anticoagulation of patients with atrial fibrillation is very effective but in the elderly, the dangers of anticoagulation must also be considered.^[12]

Uncovering the target group

Registration

An up-to-date practice database is the essential tool for primary prevention. Even the simplest of lists will have the patient's age and sex so that they can be invited for an over-70s' check. More advanced databases will allow searching by disease so that at-risk patients can be identified. For example patients for annual flu vaccinations.

Opportunistic screening

This is widely used to identify the at-risk patient and promote prevention. It can be useful in reaching patients who do not take advantage of screening initiatives or perhaps would not be included in the at-risk group. It is probably the best way to promote smoking cessation with patients.^[13]

Barriers to prevention

Taxation issues

Raising the taxation on tobacco and alcohol does reduce consumption. Only a minority of drinkers are "problem drinkers" but there is a spectrum of drinking habits. As total alcohol consumption rises or falls, the number of people in the "problem drinker" category rises or falls too.^[2] Over 40 years since the Royal College of Physicians published Smoking and Health there are still many people who smoke tobacco, including a substantial number who were not even born when the report was produced. Some are hopeless addicts and some have mental health problems. Smoking tends to be more a habit of lower social classes and raising the price may simply cause more deprivation in those sections of society that do not abstain. Raising taxation on tobacco and alcohol by a large amount may have a number of consequences:

• Consumption may fall so much that total revenue from that source falls.
• It may be very unpopular with the electorate and in a democracy politicians have to be constantly aware of the effects of their actions in terms of votes won or lost.
• It will increase smuggling, especially across open EEC borders.

Demographic issues

The major economic problem facing all developed nations today, is not the price of oil but the longevity of its people. A growing elderly population puts more strain on health and social services. The deficit in pension funds is a concern. A significant number of people now spend a quarter of their lives as old age pensioners. Smokers tend to spend less time drawing their pensions. It is often argued that smoking-related disease costs the NHS a considerable amount of money. This overlooks the earlier deaths in smokers who choose to pay significantly more tax and to live significantly shorter lives.

Most interventions have costs and do not have the advantages of revenue generation associated with, for example, taxation on tobacco. This includes screening programmes or advertising campaigns. Screening programmes also generate further costs associated with, for example, the investigation of the false positives. Immunisation programmes cost money to set up, administer and change.

The Black Report^[14] was a careful study of health inequalities with a long list of recommendations. It achieved almost iconic status when released with a misleading press statement on an August Bank Holiday Monday. Senior civil servants warned ministers that the implications were far too expensive to implement. The matter was discussed rather more fully in health and social class. It also examines "the inverse care law".^[15]

Other political barriers

Some measures generate interest from pressure groups who seek to protect personal freedoms. Politicians are keen to protect their popularity when faced with the prospect of an election. Such interests were weighed with the legislation on the wearing of seatbelts. The wearing of seatbelts in rear seats became compulsory for all in 1991.This lead to an increase in the wearing of seatbelts from 10% to 40% compared with over 90% who wear a seatbelt in the front seats.^[16] There are still 60% who break the law.

Politicians were wary about the feasibility and acceptability of restricting smoking in public places. Experience in a number of countries has shown it to be surprisingly effective and acceptable. Even smokers accept that they do need pressure to make them quit and non-smokers enjoy a smoke free environment in public spaces.

Financial and political pressures may also impair health promotion at local government level. Employers might also see promotion of healthy eating and safety at work as unaffordable. Some industries even have a financial interest in indirectly promoting unhealthy living.

Personal barriers

Cost and quality

Many people feel that expense is an impediment to a healthy lifestyle. Food labelled as "organic" is substantially more expensive and benefits are often dubious. "Convenience" or "junk food" is often not cheap and fresh fruit and vegetables are cheaper than even poor quality meat. White bread is significantly cheaper than wholemeal bread and a change in government subsidy of flour could be considered overdue. Healthy eating does not have to be expensive.

Information

Deciding what is healthy and what is unhealthy food can sometimes be difficult. Processed food, in particular, may contain a great deal of added salt, sugar and unnecessary colouring. Contents (fat, unsaturated fat, salt, sugar and other ingredients) are often on the package but not easily legible or understandable. Salt may be given as grams of salt, grams of sodium or milliequivalents. Fat content may be per package, per 100 grams or per serving. There are commercial pressures to keep the additives in food and to confound just how unhealthy some food products are.

Exercise

There may be many barriers to people taking regular exercise. This can be complex but again cost need not be a barrier. It is possible to choose recreations and pastimes that are both healthy and cheap. Building exercise into daily routines can help. For example cycling to work. This is cheaper than taking the car and could be considered a healthy option. However there are problems:

• Work must be a reasonable cycling distance away.
• The car must not be required at work.
• There should be facilities to shower and change.
• Adverse weather conditions.

Social, educational and cultural barriers

There are many examples of how these factors can present a barrier to the promotion of health. Social and cultural factors which discourage healthy lifestyles are evident in the media and in advertising. These both reflect and shape attitudes and fashions connected with unhealthy habits and behaviour. For example:

• The tobacco industry and tobacco advertising tried hard, both to discredit the research that exposed its dangers and to present its product as 'desirable'. Hollywood continued to portray smoking as "cool", sophisticated and desirable. This image worked with young people particularly. Often younger people do not consider health warnings so relevant to them whereas the images and positive attributes of smokers portrayed in advertising and films can be alluring.
• Peer pressure is what drives young people to experiment with drugs and to drive dangerously. Alcohol consumption amongst the young is a major concern and the associated problems are discussed in the article on cirrhosis. As well as physical disease there are accidents and violence. Binge drinking, especially by young women, is a particular cause for concern. Peer pressure may also lead to unsafe sex.
• Misinformation, ignorance and lack of education can all lead people to miss out on healthy choices or to adopt an unhealthy lifestyle. The BBC and ITV have in the past undermined the MMR vaccine by referring to it as "the controversial MMR vaccine" and implying that significant scientific uncertainty persists.

Administrative barriers

Badly run prevention programmes are often responsible for lack of effectiveness. Inadequate lists, unachievable targets and lack of follow-up for non-responders are typical problems. The greatest barrier to effective prevention is lack of effectiveness in modifying the risk factors in patients identified as at-risk. The "rule of halves" is often quoted. It is applied classically to the management of hypertension but is valid for many chronic conditions.^[17] "Half of patients with hypertension are identified, half of these receive any treatment and only half of these are treated effectively". This notion is rather old and we should be doing rather better by now but we may not be.^[18]

Role of prevention in General Practice

Prevention is better than cure. It has to be, but the management of change is a complex and difficult issue, not least transformation of lifestyles. There is ignorance. There is indolence. There are social and commercial pressures. The words of the General Confession in Archbishop Cranmer's Book of Common Prayer seem most apt. We have done those things that we ought not to have done and we have left undone those things that we ought to have done and there is no health in us.

Doctors, educators and politicians have a duty to ascertain that the facts are delivered to the populace in a form that they can comprehend. What is rather more contentious is the degree to which prevention should be enforced. If a Jehovah's Witness is allowed to refuse a life-saving blood transfusion, is not a "couch potato" allowed to choose indolence and an early death? "You can take a horse to water but you cannot make it drink."

In recent decades General Practice has, quite appropriately, embraced prevention to help produce a National Health Service, rather than just a National Sickness Service. What has been achieved is most laudable although much more is possible. It is wrong to hold doctors responsible for the shortcomings of their patients but we have to do our best to convince even the stubborn and sceptical. Hence a half hearted approach to prevention is useless. You have to believe in your message and promote it enthusiastically.