3.4 Combining prevention levels to promote public health
To illustrate how the hierarchy of prevention levels can operate in practice, consider our answers to the following worked example.
What measures can be taken against TB at the primary, secondary and tertiary levels of prevention?
Primary prevention: BCG vaccination and improved living standards, including better housing (reduction in crowding) and nutrition (improved host immunity).
Secondary prevention: screening programmes to detect cases of infection early (e.g. from sputum tests); treatment of early non-symptomatic infection with drugs such as isoniazid, or symptomatic TB with a multidrug regimen, ideally in a DOTS programme (see Box 2).
Tertiary prevention: drug treatment of severe complications such as tubercular meningitis, and physical rehabilitation therapy for extrapulmonary TB, e.g. affecting the skeleton and mobility. (Note: ‘extrapulmonary’ means ‘outside the lungs’.)
The same principles can be applied to other examples.
Identify the level of prevention operating in each of the following strategies to control diarrhoeal diseases in children in a rural village in a low-income country.
- Drilling a deep tube well to access clean water and pumping it to standpipes.
- Digging cesspits and building latrines.
- Vaccinating children against rotaviruses.
- Teaching parents how to make and administer oral rehydration salts (ORS) to children with acute diarrhoea.
- Educating parents and children about the importance of hand washing before preparing food and after defaecation or urination.
- Administering intravenous fluids to children with severe dehydration caused by persistent diarrhoea.
Strategies 1–3 and 5 are examples of primary prevention to reduce the number of new cases of diarrhoeal diseases.
Strategy 4 is secondary prevention because ORS shortens the duration of the illness in infected children, which reduces the spread of causative organisms. However, it may also be life-saving – and therefore a tertiary prevention strategy for some children.
Strategy 6 is tertiary prevention, aimed at saving lives.
Box 2 Directly observed therapy, short course (DOTS)
In order to control TB, patients must regularly take antibiotics over a prolonged period of several months. Failure to do so can lead to a relapse of patient health and the possible development and spread of drug-resistant forms of TB.
In order to improve drug compliance in patients, the WHO devised a five-component TB control strategy called 'directly observed therapy, short course' (DOTS). DOTS addresses the problem of drug compliance by having either a designated health worker or some other responsible person directly observe a patient each time they take their antibiotics. This simple observation strategy (listed below as item 3) is further supported by an additional four aspects of medical and political infrastructure:
- political commitment with increased and sustained financing
- case detection through quality-assured bacteriology
- standardised treatment with supervision and patient support
- an effective drug supply and management system
- monitoring and evaluation system and impact measurement