The 4 types of epidemic and their characteristics

Epidemics are not new events in human history, but have occurred throughout.. The Spanish plague, measles or the Spanish flu are examples. The emergence of new infectious diseases has significantly influenced the course of human evolution.

The generation of infectious epidemics is not uncommon, it is more common than many realize. But thanks to the advancement of our knowledge in the field of health, the impact is less than it could have been in the past. The study of these phenomena has made it possible to know more about them, how they are at the origin or differentiate the different types of epidemics, and thus have an advantage in the fight against their consequences.

What is an epidemic?

We cannot continue with the topic if we do not know this concept before. From the Greek Epi, which means “envelope”, and Dan, which is “village”, is understood as an epidemic when there is a significantly high increase in cases of a particular disease in a specific location, over a period of time determined. . As can be gleaned from this definition, to declare that an epidemic is in progress requires a rapid spread of a particular condition in a given population in a very short time.

Previously, this term was associated with infectious diseasesThat is to say the discomfort caused by invasive external agents (bacteria, viruses, …); and contagious, which is person-to-person transmission, but as we will see with the different types of outbreaks, this word has spread to other types of conditions. Even the World Health Organization (WHO) describes obesity as an epidemic.

How epidemics happen

It is clear that if there is no condition, there can be no epidemic. But as we can see, they always appear over time, and although we are currently speaking specifically of COVID-19 for its global impact, which will be discussed later, they appear from time to time in some sort of epidemic. certain countries.

In the simplest case to explain, it is with an infectious disease. The pathogen or infectious agent, for example viruses or parasites, is found in a natural reservoir, such as standing water or in a specific animal that does not cause symptoms, and when environmental conditions change, it made either a lower temperature or a higher ambient humidity, can be transmitted and reach people, causing them discomfort, activating their immune system.

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

Classes of epidemics

Scientists in charge of studying these phenomena, in other words, epidemiologists looked for any information that could give the appearance of epidemics for better prevention against them.

As for example its origin, and this is the criterion used to differentiate the different types of epidemics that exist, which are as follows.

1. Common origin

This category includes outbreaks that occur when a group of people are infected to be exposed to a common source but there is no person-to-person transmission. With an example, it is much better understood. In a fictitious case, a group of people from a restaurant are admitted to a hospital with digestive discomfort due to a Salmonella infection. As we can extract from here, the common origin of all these patients is to have eaten in the aforementioned restaurant of the food containing the infectious bacteria, but there was no transmission between the people who were there. at the scene because Salmonella does not. capacity.

This type of epidemic is subdivided into three sub-categories, the first being that we have exposed the case of “punctual”That is, it only took one moment of contact with the source of the infection to get the condition.

Another of the subtypes is “continuous”, that is, when continuous contact with the source of the problem is necessary to fall into the disease. An example would be if there was a breakdown in the water purification system and people in the population who received it continuously drink it, there would come a time when they would have problems in the digestive system due to the bacteria. living there. water, but they need to drink continuously for a while to have symptoms.

Finally there would be the cases of “intermittent”, which would be similar to the previous one, but it is not necessary that a continuous exposure at the origin, but neither with a single contact is entrusted.

2. Propagation

In this type of epidemic, there is no common source, but it is spread from person to person, with great frequency. and they are increasingly affected by the disease. A clear example is the seasonal flu caused by the influenza virus.

Transmission can be direct (by air, by sexual relations, etc.) but also of an indirect form such as the use of vehicles (for example the contagion of the HIV virus to share syringes) or by means of vectors ( example of yellow fever and mosquito bites between people).

3. Mixed

In the next type of epidemic would be the case of mixed, which is the mixture of the two above. In other words, people get the infection from a common source, but then they pass it on to other people. We can put the case of an epidemic of shigellosis, which results in a gastrointestinal infection, which occurs in a population during the celebration of its holidays.

People ingest a product that contains Shigella, the bacteria that causes the disease. People return to their hometowns after partying and after an incubation period, show symptoms and infect others around them. The original source is a product at the party but the spread is due to people turning it over to others and taking it elsewhere far from the origin. The truth is, these cases are the most colorful.

4. Others

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

Examples are Lyme disease, a disease caused by bacteria of the genus Borrelia which is transmitted by ticks from rodents to humans. Obesity could also be included, as it is a complex disorder, but the WHO calls it an epidemic, but it is already more complicated to speak because there is no infectious agent nor contagion.

Endemic, epidemic and pandemic

While these are not types of outbreaks, they are three closely related concepts. If we remember, an outbreak would be an event that occurs with an unusual increase in patients with the same condition, in a given population in a specific period of time. But in the event that this disease lengthens over time and periodically appears in a particular place, then it becomes endemic.

On the other hand, if an epidemic is moving rapidly to more places, reaching global spread, then we are talking about a pandemic. A curious fact about this is that in 2009 the WHO changed its definition, because previously in addition to affecting multiple countries simultaneously, it also had to have a high death rate to consider an epidemic as a pandemic. Now, the disease does not need to be high lethal to be classified in this way.

Unfortunately, these days we were able to verify how a virus in the Coronaviridae family, SARS-CoV-2 (known as Coronavirus), was transmitted from animals (pointed at the pangolin, an armored mammal) to humans, and then it spread rapidly through the population of China, being at that time an epidemic, then moving towards rapid global spread, at which point it became a pandemic. The problem is, this is a new condition, so we must continue to study and follow the recommendations that come to us from the scientific community.

It is up to all of us to follow the advice not to spread it and thus to reduce the number of infected, to stop the progression of the disease and be able to treat all patients without saturating the health of the country.

Bibliographical references:

  • Joan Pau Horcajada and Belén Padilla. “Endemic and epidemic. Investigation of a nosocomial epidemic.” 2012. https://seimc.org/contenidos/documentoscientificos/eimc/seimc_eimc_v31n03p181a186.pdf

  • US Department of Health and Human Services. “Principles of Epidemiology in Public Health Practice”. Third edition. 2012. https://www.cdc.gov/csels/dsepd/ss1978/SS1978.pdf

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