End of September 2026: in Year 4 of the vocational school’s Health and Social Care Services track, Hygiene and Medical-Health Culture opens the programme with epidemiology and prevention, before moving on to infectious diseases and chronic-degenerative ones. The first test typically falls between the end of October and November: from now there are about five to eight weeks to go. It is a topic made almost entirely of definitions to keep apart. The three levels of prevention are similar enough to get confused in an oral test, but they follow a precise logic once it is understood.
If last year you followed the Year 3 programme (cell, tissues, body systems, medical terminology), this topic is the direct continuation of that path: I wrote about it in Hygiene in Year 3: how to study it. Here I take that foundation for granted and start from where the subject restarts in Year 4: what health is, how the spread of a disease is measured, and the three ways of preventing it.
Health according to the WHO
The starting point of the programme is the definition of health given by the World Health Organization: health is not simply the absence of disease, but a state of complete physical, mental and social well-being. This is a definition that should be quoted in full in your work, because the piece that almost everybody forgets is precisely “mental and social”: a person with no diagnosed illness but socially isolated or in a condition of severe psychological distress does not, by this definition, count as being in a state of full health.
Epidemiology: incidence and prevalence
Before talking about prevention, the subject introduces two basic measures to describe how widespread a disease is in a population. They are the two terms that are confused most often, because they seem to say the same thing and in fact answer different questions.
- Incidence: the number of new cases of a disease that appear in a population during a certain period of time, in relation to the population at risk. It answers the question: how many people fell ill in this period?
- Prevalence: the total number of cases present in a population at a given moment (new and old together), in relation to the total population at that moment. It answers the question: how many people are ill right now?
The practical difference: a short-lasting disease (flu) can have a high incidence but a low prevalence at a given instant, because the sick recover quickly; a chronic disease (diabetes) can have a low incidence in one year but a high prevalence, because cases accumulate over time without recovering.
Two worked calculations
Calculation 1: Incidence. In a town of 10,000 inhabitants, over the course of a year 50 new cases of a certain disease are recorded. What is the incidence?
Expressed as a rate per 1,000 inhabitants per year: new cases per 1,000 inhabitants per year.
Calculation 2: Prevalence. In a population of 5,000 people, at a given moment 200 people are affected by a chronic disease (including both the cases diagnosed this year and those of previous years that are still ongoing). What is the prevalence?
Expressed as a percentage: 4% of the population, that is 40 cases per 1,000 inhabitants.
The three levels of prevention
Prevention is classified according to the moment at which it intervenes with respect to the natural history of the disease: before it appears, as soon as it appears, or after it has already appeared.
Primary prevention
It intervenes before the disease appears, acting on the causes or risk factors in a healthy population. Typical examples: vaccinations, health education (campaigns on diet, smoking, physical activity), environmental hygiene (making water safe to drink, waste disposal, food controls). In Italy some vaccinations were made compulsory by a law of 2017 (Law 119/2017): it is a concrete example of primary prevention imposed by legislation, as well as recommended.
Secondary prevention
It intervenes when the disease is already present but not yet symptomatic, with the aim of detecting it as early as possible: this is early diagnosis, typically through the screening of at-risk populations, even if they have no symptoms. Tests such as the Pap test or the mammogram fall into this category (for the starting age and frequency, which vary over time and by risk group, the reference remains the official website of the Ministry of Health, not a number from an old textbook). Diagnosing early a disease that is already under way almost always improves the prognosis, even when it is not possible to prevent its onset.
Tertiary prevention
It intervenes when the disease has already appeared and perhaps has already been treated: the aim is no longer to avoid it or to discover it, but to avoid relapses and complications, and to recover lost function. Typical example: rehabilitation after a stroke or a heart attack, to regain independence and reduce the risk of a new event.
Typical mistakes to avoid
The point where the class divides most is telling secondary from tertiary: both intervene “afterwards” in some sense, but secondary prevention intervenes when it is not yet known that the disease is there (that is why screening is done on people without symptoms), while tertiary prevention intervenes when the disease is already known and overt, and the work is on its consequences. Another frequent mistake is to classify as “primary” anything that sounds generically good for health (eating well, doing sport): it is primary only if the explicit aim is to prevent the disease from arising, not a generic well-being.
The chain of infection of infectious diseases
For an infectious disease to be transmitted from one person to another, three elements are needed in sequence, called the chain of infection (the epidemiological chain):
- Reservoir: where the infectious agent normally lives and multiplies. It may be a human (sick or a healthy carrier), an animal, or the environment (water, soil).
- Route of transmission: the path by which the agent passes from the reservoir to a new host. It is divided into direct transmission (direct physical contact, respiratory droplets at short distance) and indirect transmission, in turn through vehicles (water, food, contaminated objects) or vectors (living organisms, typically insects, that carry the agent from one host to another, like the mosquito for malaria).
- Susceptible host: a person without immunity (through vaccination or a previous infection) in whom the agent can settle and replicate.
The reason this chain is studied is practical: every measure for preventing infectious diseases works by breaking one of these three links. Isolating a sick person or cleaning up an animal reservoir acts on the first link; hand washing, water disinfection and protection from insects act on the second; vaccination acts on the third, making the host no longer susceptible.
Herd immunity, conceptually
When in a population the share of immune people (through vaccination or recovery) is high enough, the chain of transmission is broken even for the few people who are still susceptible: the infectious agent, looking for a new host, finds itself surrounded mostly by immune people and cannot spread. This phenomenon is called herd immunity, and it is the reason why vaccinating most of a population indirectly protects also those who cannot be vaccinated (because of age, illness or other medical contraindications). The exact coverage threshold needed varies from disease to disease and is not a number to learn in general: what matters for the test is the mechanism, not a percentage.
Three cases: which level of prevention do they belong to?
Case 1: A school organises a course on food education to prevent obesity in teenagers.
It is primary prevention: the target population does not (necessarily) already have the disease, and the intervention acts on a behavioural risk factor before any illness appears.
Case 2: A woman with no symptoms undergoes a routine cancer screening recommended for her age group.
It is secondary prevention: the person is asymptomatic, and the aim of the test is to detect early a disease that might already be present but not yet visible, in order to intervene as soon as possible.
Case 3: A patient recovering from a heart attack follows a cardiac rehabilitation programme to regain exercise capacity and reduce the risk of a second event.
It is tertiary prevention: the disease has already appeared and has partly been treated; the intervention works on the consequences and on the prevention of relapses, not on the discovery of the disease or on avoiding its initial onset.
How to answer an open question on this topic
The typical test format for this subject is a short open question plus a few tick-box items (the same pattern described in the Year 3 post). When you are asked to classify an intervention, do not just give the label (“it is secondary”): explain why, that is, at what moment in the natural history of the disease that action intervenes in relation to the appearance of symptoms. It is that explanation, not the label alone, that shows you have understood the logic and have not just memorised three examples.
Where to go next
There is not yet a practice test dedicated to Hygiene and Medical-Health Culture on the site: the practice tests you find for now cover other subjects, and it is not something I promise you for the moment. For the rest of the science programme you will find the overall picture on the science tutoring page; if you need a hand setting up this chapter before the test, the introductory call is free and lasts half an hour. For food hygiene see HACCP and food contamination: a guide to the test; for the calculations on energy requirements, basal metabolic rate and energy requirements.
