Difference between epidemic and pandemic


Epidemic is a term that is widely used to describe any problem that is out of control. An epidemic is defined as "an outbreak of a disease that occurs over a wide geographic area and affects an extremely large proportion of the population. "

An epidemic is an event in which a disease is actively spreading . Rather, the term pandemic refers to geographic spread and is used to describe a disease that affects an entire country or the entire world .

While casual use of the term "epidemic" may not require this nuance, it is important to be aware of the differences between the two (and similar terms such as " outbreak " and " endemic ") when watching public health news. Furthermore, from an epidemiological perspective, these terms guide the public health response to better control and prevent diseases.

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General confusion

While the epidemic Commonly used to describe health problems (for example , the opioid crisis in the United States has risen to epidemic proportions ), it is sometimes used colloquially to describe behavior (there is an epidemic of tantrums among preschoolers! ) or behavioral phenomena (such as "epidemic hysteria"). ').

While these practices are not unacceptable in the current context, they can cause confusion. Also, even when the word is used to define health problems, it may not accurately represent the extent or progression of the disease. In some cases, terms such as "outbreak" or "endemic " may be more appropriate. In other cases, the epidemic may not match the scale of the problem and is better defined as a pandemic.

On March 11, 2020, the World Health Organization described COVID-19 as a pandemic.

Classification of disease events

Epidemiology is a branch of medicine that deals with the incidence, spread, and control of diseases. In the United States, the main body that collects and monitors this data is the Centers for Disease Control and Prevention (CDC). Among its many functions, the CDC is called upon to direct the appropriate response to the onset of the disease.

While the incidence rate can be described in different ways, it is primarily determined by two measurable factors:

  • The pattern and speed at which the disease spreads (known as the rate of reproduction)
  • Vulnerable population size (known as critical community size)

The role of epidemiology is to determine disease prevalence (the proportion of people affected in a population) and incidence (the occurrence of a disease over a period of time) in order to guide an appropriate public health response.


Depending on the prevalence, incidence, and known or unknown pathways of the disease, an epidemiologist can describe an event in several ways:

  • Sporadic is a disease that occurs infrequently or irregularly. Foodborne pathogens, such as Salmonella or E. coli , can often cause sporadic outbreaks of illness.
  • A group refers to a disease that occurs in large numbers, even if the actual number or cause may be uncertain. An example is the cluster of cancer cases that are often reported after an accident at a chemical or nuclear power plant .
  • Endemic disease is understood to be the persistent presence and / or habitual prevalence of the disease in a geographic population .
  • Hyperendemic refers to high and persistent rates of disease, well above those seen in other populations. For example, HIV is hyperendemic in parts of Africa, while one in five adults has the disease and it is endemic in the United States, where approximately one in 300 people are infected .
  • An epidemic means a sudden increase in the number of disease cases beyond what is expected .
  • An outbreak has the same definition as an epidemic, but is often used to describe a more limited geographic event .
  • A pandemic is an epidemic that has spread to several countries or continents and usually affects large numbers of people .

In contrast, plague is not an epidemiological term, but a term that specifically refers to a contagious bacterial disease characterized by fever and delirium, such as bubonic plague .

Epidemic versus pandemic

Although the terms may imply a certain threshold at which an event is declared an outbreak, epidemic, or pandemic, the distinction is often not clear, even among epidemiologists.

This is partly due to the fact that some diseases become more common or fatal over time, while others are less common, forcing the CDC to regularly adjust its statistical models.

Epidemiologists are careful when describing a disease event to put it in context. While an epidemic suggests a disease that is out of control, events described as clusters suggest an isolated event of least concern.

The CDC also recognizes that certain terms can cause unnecessary panic. One such example is the Zika virus outbreak in 2016, which caused alarm in the United States when the local disease affected 218 people in Florida and six people in Texas. Another 46 were infected through sexual contact or laboratory transmission, and another person was infected person-to-person by unknown means .

Even with HIV, a disease that has spread across much of the planet, the term pandemic is increasingly being replaced by an epidemic , given the widespread adoption of effective treatments and declining rates in some previously hyper-prevalent regions.

On the other hand, as the flu becomes more dangerous year after year, health officials commonly refer to seasonal outbreaks as pandemics, especially given the 2009 US H1N1 flu outbreak that affected more than 60 million Americans, resulting in 274 hospitalizations, 304 people. 12,469 deaths .

This does not mean that pandemics should be treated in the same way as more limited outbreaks, given the need for international cooperation. On the other hand, an outbreak can be treated as aggressively as a pandemic if it can spread beyond its borders, as is the case with the Ebola virus .

Feelings of fear, anxiety, sadness, and insecurity are normal during pandemics. Being proactive about your mental health can help you strengthen both your mind and body. Discover the best online therapy options available to you .

Pandemic phases

While there are procedural steps that the CDC will take to assess and classify a disease event, the actual stage of an epidemic (essentially, a diagram of when the spread of a disease is severe enough to take a specific action) can vary. according to pathogenesis. (pathway) of disease and many other epidemiological factors.

The one-stage model used to guide the public health response deals specifically with influenza (influenza). In 1999, the World Health Organization (WHO) published the first influenza pandemic preparedness plan, which outlined an adequate response based on six well-defined stages .

The aim of the plan was to coordinate the global response by providing countries with a blueprint from which to develop their own national strategies based on available resources. The United States launched its first influenza pandemic plan in 2005. The same basic model can be applied with variations to other epidemics such as tuberculosis , malaria , and Zika.

Steps 1-3 are designed to help public health officials understand when it is time to develop tools and action plans to respond to an imminent threat. In stages 4 to 6, action plans are implemented in coordination with WHO.

WHO revised the milestones in 2009 to better distinguish between preparedness and response. The plan was intended solely to combat influenza pandemics, given its high mutation rates and the virus's ability to spread from animals to humans .

Previous Stages of a WHO Influenza Pandemic

  • Phase 1 is the period during which animal viruses do not cause infection in humans.
  • Phase 2 is the first threat level when the virus is confirmed to have passed from animal to human.
  • Phase 3 is when sporadic cases or small clusters of diseases are confirmed, but person-to-person transmission has not occurred or is considered unlikely to sustain an outbreak.
  • Phase 4 is the time when transmission of the virus from person to person or virus from person to animal has triggered a community-wide outbreak.
  • Phase 5 is when person-to-person transmission of the virus has spread the disease in at least two countries.
  • Phase 6 is the time when a disease is declared a pandemic that has spread to at least one other country.

The time frame for each stage can vary significantly from months to decades. Not everyone will progress to phase 6, and some may even return if the virus spontaneously weakens.

As of February 2020, the WHO has discontinued this six-step plan.

Notable pandemics in history

In addition to HIV, which has killed more than 39 million people since 1982, there have been other equally devastating pandemics in history:

  • Plague of Justinian AD 541 was associated with the bubonic plague and killed 25-50 million people in one year .
  • The Black Death killed more than 75 million people between 1347 and 1351, including those who died in the Middle East, China and India and Europe .
  • The 1918 Spanish flu pandemic killed more than 50 million people in one year, including 675,000 Americans .
  • The smallpox pandemic of the 20th century claimed between 300 and 500 million lives. Edward Jenner confirmed that the vaccine provided protection against smallpox in 1798. In 1959, the World Health Organization (WHO) launched a massive campaign to eradicate smallpox globally. Smallpox, the only human disease eradicated to date, was declared eradicated in 1980 .
  • The ongoing tuberculosis pandemic continues to kill more than 1.5 million people each year. Despite the availability of effective treatments, multidrug resistance has hampered efforts to reverse the pandemic .

The information in this article is current as of the date shown, which means that more information may be available when you read it. For the latest updates on COVID-19, visit our Coronavirus News page .

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