The 4 Types Of Epidemic, And Their Characteristics
Epidemics are not new events in human history, 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 future of human evolution.
The generation of infectious outbreaks is not at all unusual, it is more common than many may think. But thanks to the advancement of our knowledge in the field of health, the impact is less than it could be in the past. The study of these phenomena has allowed us to learn more about them, how they originate or differentiate different types of epidemics, and thus have an advantage when combating their consequences.
We cannot continue with the topic if we do not first know this concept. From the Greek Epi, which means “about”, and Demos, which is “town”, an epidemic is understood when there is a significantly high increase in cases of a specific disease in a specific location, during a certain period of time. As can be extracted from this definition, to affirm that an epidemic outbreak is occurring, there must be a rapid spread of a specific condition in a specific population in a very short time.
This term was previously associated with infectious diseases, that is, discomforts that are caused by invasive external agents (bacteria, viruses,…); and contagious, that there is transmission from person to person, but as we will 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 condition, there cannot be epidemic outbreaks But as we can see, they always appear over time, and although currently we are talking specifically about COVID-19 due to its global impact, which will be talked about later, some type of outbreak appears from time to time in some country.
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 stagnant water or within a specific animal that does not cause symptoms, and when environmental conditions change, whether the temperature is lower or higher environmental humidity, it can be transmitted and reach people, causing discomfort in them, activating their immune system.
As we can see, there are many factors for this to occur, and even more so for it to become a type of epidemic, such as an increase in the pathogen’s ability to cause the disease (a concept known as virulence), environmental conditions ( temperature, humidity…) and conditions of the host, in our case people (current level of immune system, deterioration due to previous conditions,…).
Types of epidemics
The scientists in charge of studying these phenomena, in other words, Epidemiologists have searched for any type of information that could provide the appearance of outbreaks for better prevention against them.
For example, how it originates, and this is the criterion used to differentiate the different types of epidemics that exist, which are the following.
1. Of common origin
This category includes outbreaks that originate when a group of people are infected by exposure 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 due to digestive system discomfort due to a Salmonella infection. As we can extract from here, the common origin of all these patients is having eaten food in the aforementioned restaurant that contained the infectious bacteria, but there has been no transmission between the people who were in the premises, since Salmonella does not have that capacity.
This type of epidemic is subdivided into three subcategories, the first one that we have exposed being the “punctual” case that is, only a single moment of contact with the source of the infection has been needed to obtain the condition.
Another subtype is “continuous,” which is when continued 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 it continually drank 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 develop symptoms.
Lastly, there would be the “intermittent” cases, which would be similar to the previous one, but continuous exposure to the source is not necessary, but neither is it contagious with a single contact.
2. Propagation
In this type of epidemic there is no common source but it spreads from person to person, with great frequency and there are more and more people affected by the disease. A clear example is the seasonal flu caused by the influenza virus.
Transmission can be direct (through the air, through sexual relations,…) but also indirectly such as the use of vehicles (for example, the spread of the HIV virus by sharing syringes) or through vectors (for example, yellow fever). and the mosquito that bites between people).
3. Mixed
In the next kind of epidemic it would be the case of the mixed one, which It is the mixture of the previous two That is, people get the infection through a common source but then transmit it to other people. We can consider the case of an outbreak of shigellosis, which translates into gastrointestinal infection, that occurs in a population during the celebration of its holidays.
People ingest a product in it that carries Shigella, the bacteria that causes the disease. People return to their municipalities of origin after the festival and after an incubation period they 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 infecting others and taking it to other points far from the origin. The truth is that these cases are the most striking.
4. Others
And finally, here we group the types of epidemics that do not meet the requirements to be considered part of the previous ones. Cases of zoonoses are included here, which are diseases transmitted from animals to humans only.
An example is Lyme disease, a condition caused by the 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 describes it as an epidemic, but that is more complicated to talk about, since there is no kind of infectious agent or contagion.
Although these are not types of epidemics, they are three concepts that are closely linked to each other. If we remember, an epidemic would be an event in which an unusual increase in patients affected by the same condition occurs in a specific population in a specific period of time. But if this disease lasts over time and appears periodically in a specific location, then it becomes endemic.
On the other hand, if an epidemic outbreak moves quickly to more locations, reaching global 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 a high mortality to consider an outbreak as a pandemic. Now it is not necessary for the disease to have a high lethality to be classified in this way.
Unfortunately, these days it is something that we have been able to verify as 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 which subsequently had a rapid spread in the population of China, being at first an epidemic outbreak, then rapidly spreading worldwide, at which point it was classified as a pandemic. The problem with this is that it is a new condition, so we must continue studying and follow the recommendations that come to us from the scientific community.
It is in the hands of all of us to follow the advice to avoid getting infected and thus reduce the number of infected people to stop the advance of the disease and be able to care for all patients without saturating the country’s healthcare.
