The 4 types of epidemics and their characteristics

Not all epidemics are transmitted in the same way and do not represent a danger to public health.

Epidemics are not new events in the history of mankind, but have been occurring throughout it.. The Black Death, measles or the Spanish flu are examples of this. The emergence of new infectious diseases has significantly influenced the course of human evolution.

The generation of infectious outbreaks is nothing unusual, it is more common than many may think. But thanks to the progress of our knowledge in the field of health, the impact is less than it might have been in the past. The study of these phenomena has allowed us to know more about them, how they originate or differentiate different types of epidemics, and thus to have an advantage when fighting with their consequences.

What is an epidemic?

We cannot continue with the subject if we do not know this concept first. From the Greek Epi, which means "on", and Demos, which is "people", an epidemic is understood as when there is a significantly high increase of cases of a specific disease in a specific location, during a specific period of time. As can be seen from this definition, in order for an epidemic outbreak to occur, there must be a rapid spread of a particular condition in a given population in a very short time.

In the past, this term was associated with infectious diseasesthat is, ailments that are caused by invasive external agents (bacteria, viruses, etc.); and contagious, where there is person-to-person transmission, but as we shall see with the different types of epidemics, this word has been extended to other types of conditions. Even the World Health Organization (WHO) classifies obesity as an epidemic.

How outbreaks occur

It is clear that if there is no disease, there can be no outbreaks.. But as we can see, they always appear over time, and although we are currently talking specifically about COVID-19 because of its global impact, which will be discussed later, from time to time some kind of outbreak appears in some country.

The simplest case to explain is with an infectious disease. The pathogen or infectious agent, for example a virus or parasite, is found in a natural reservoir, such as stagnant water or inside a specific animal that does not cause symptoms, and when environmental conditions change, whether the temperature is lower or the humidity is higher, it can be transmitted and reach people, causing them to feel ill, activating their immune system.

As we can see, there are many factors for this to occur, and even more for it to become a type of epidemic, such as an increase in the pathogen's capacity to cause disease (a concept known as virulence), environmental conditions (temperature, humidity...) and host conditions, in our case people (current level of immune system, deterioration due to previous conditions,...).

Types of epidemics

The scientists in charge of the study of these phenomena, in other words, epidemiologists, have looked for any kind of epidemic, epidemiologists have been looking for any kind of information that can provide the occurrence of outbreaks for better prevention against them.

Such as how it originates, and this is the criterion used to differentiate the different types of epidemics that exist, which are as follows.

1. Of common origin

This category includes outbreaks that occur when a group of people are infected by exposure to a common source but there is no person-to-person transmission. An example makes it much easier to understand. In a fictitious case, a group of people from a restaurant are admitted to a hospital for digestive system discomfort due to a Salmonella infection. As we can extract from this, the common origin of all these patients is to have eaten food containing the infectious bacterium in the restaurant, but there has been no transmission among the people who were in the restaurant, since Salmonella does not have that capacity.

This type of epidemic is subdivided into three subcategories, the first of which is the case of "punctual", i.e., it has only been necessary to treat a single case.that is to say, only a single moment of contact with the source of infection was necessary to obtain the infection.

Another of the subtypes is "continuous", which is when continuous contact with the source of the problem is required to fall into the disease. An example would be if there was a breakdown in the water purification system, and the people of the population that receives this water drank continuously from it, there would come a time when they would have problems in the digestive system due to the bacteria that live in the water, but they need to be drinking continuously over a period of time to present symptoms.

Finally there would be the cases of "intermittent", which would be similar to the previous one, but it is not necessary a continuous exposure to the source, but neither with a single contact is contagious.

2. Spread

In this type of epidemic there is no common source but it spreads from person to person, with a high frequency, and more and more people are affected by the disease. and more and more people are affected by the disease. A clear example is the seasonal influenza caused by the influenza virus.

Transmission can be direct (through the air, sexual intercourse, ....) but also indirect, such as the use of vehicles (e.g. HIV virus transmission by sharing syringes) or through vectors (e.g. yellow fever and mosquito bites between people).

3. Mixed

The next type of epidemic is the case of mixed epidemics, which is a mixture of the two previous ones. is a mixture of the two previous ones. That is to say, people get the infection through a common source but then they transmit it to other people. We can take the case of an outbreak of shigellosis, which translates into Gastrointestinal infection, occurring in a population during the celebration of their holidays.

People ingest a product that carries Shigella, the bacterium that causes the disease. People return to their townships of origin after the party and after an incubation period show symptoms and infect other people around them. The source of origin is a product at the party but the spread is due to people who infect others and have taken it to other points far from the origin. The truth is that these cases are the most striking.

4. Other

And finally, here are grouped the types of epidemics that do not meet the requirements to be considered part of the above. Cases of zoonosis are included here, which are diseases transmitted from animals to humans only.

Examples are Lyme disease, a condition caused by bacteria of the genus Borrelia that is transmitted by ticks from rodents to humans. Obesity could also be included, since it is a complex disorder but the WHO classifies it as an epidemic, but that is more complicated to talk about, since there is no infectious agent or contagion of any kind.

Endemic, epidemic and pandemic

Although they are not types of epidemics, they are three concepts that are closely linked to each other. If we recall, an epidemic would be an event in which there is an unusual increase in the number of patients affected by the same condition in a given population in a specific period of time. But in the event that this disease is prolonged in time and appears periodically in a specific location, then it becomes an endemic.

On the other hand, if an epidemic outbreak moves rapidly to more locations, reaching a worldwide spread, then we speak of a pandemic. A curious fact about this is that in 2009, the WHO changed its definition, since before, in addition to affecting several countries simultaneously, it also had to present high mortality to be considered a pandemic outbreak. Now it is not necessary for the disease to have a high lethality to be classified in this way.

Unfortunately, these days we have seen how a virus of the Coronaviridae family, SARS-CoV-2 (known as Coronavirus), has been transmitted from animals (the pangolin, an armored mammal, was targeted) to humans, and then has had a rapid spread in the population of China, being at first an epidemic outbreak, then moving on to a rapid global spread, at which point it was classified as a pandemic. The problem with this is that it is a new condition, so we must continue to study and follow the recommendations of the scientific community.

It is in the hands of all of us to follow the advice to avoid infection and thus reduce the number of infected people, to stop the advance of the disease and to be able to treat all patients without saturating the country's healthcare system.It is up to all of us to follow the advice to avoid becoming infected and thus reduce the number of infected people, to stop the advance of the disease and to be able to attend to all patients without saturating the country's healthcare system.