Original Editor - Kim Jackson Top Contributors - Kim Jackson, Lucinda hampton, Tony Lowe, Tarina van der Stockt and Nicole Hills

Infectious diseases are spread by either bacterial or viral agents and are ever-present in society. Usually infected cases are present in numbers below an expected thresholdA but every once in a while there may be an outbreak, a new strain or a new disease that has a significant impact at either a local or global level<1>. The spread and rate of new cases can be classified as<1>:

Endemic - describes a disease that is present permanently in a region or populationEpidemic - is an outbreak that affects many people at one time and can spread through one or several communitiesPandemic - is the term used to describe an epidemic when the spread is global.

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Endemic is derived from Greek en meaning in and demos meaning people. It is used to describe a disease that is present at an approximately constant level within a society or country. Each country may have a disease that is unique, for example



An epidemic is derived from Greek epi meaning upon or above and demos meaning people and is the term used to describe a situation where a disease spreads rapidly to a large number of people in a given population over a short time period.

The term epidemic is not just used with infectious diseases. It is also used with any scenario that leads to a detrimental rise of health risks within a society. eg.

When the term epidemic is used in connection with infectious diseases it is due to the sudden rise of cases usually resulting from a new infectious agent or a change in an existing agent, for example:

Epidemics can follow predictable patterns and these trends are often used to monitor, predict and control the spread of the infection. A typical example of this is seasonal flu.



A pandemic is derived from Greek pan meaning all and demos meaning people and is the term used to describe the rapid spread of a transmissible infectious/communicable disease over several continents or worldwide. Once an epidemic becomes global and affects a large percent of the population it becomes known as a pandemic. The terms pandemic and epidemic are used to describe the rate and distance of the spread of the disease and not the severity of the disease. Significant features of a pandemic are listed below:

Affects a wider geographical area, often globalInfects a very large number of peopleOften caused by a new virus or a new strain of a virus that has been dormant for many years.Spreads quickly in humans as there is little to no existing immunityCan cause a high number of deathsBecause of the need to control the spread of the disease, there is often social disruption, unrest and economic loss

Escalation of an Epidemic to a Pandemic

The World Health Organization (WHO) will declare a Pandemic when a disease has shown exponential growth - dramatically increasing rate of growth, each day showing many more cases than the previous day. A current example of this is the Coronavirus Disease (COVID-19). On 31 December 2019, a cluster of cases of pneumonia of unknown cause, in the city of Wuhan, Hubei province in China, was reported to the WHO. This was subsequently identified as a new virus in January 2020 and over the following months, the number of cases continued to rise but were not contained to China and showed exponential growth worldwide. Due to the rapid global rise in cases, this was declared a pandemic on 11 March<9> and globally, as of 4:22pm CET, 9 December 2020, there have been 67,780,361 confirmed cases of COVID-19, including 1,551,214 deaths, reported to WHO.s<10>

Stages of a Pandemic

The WHO has identified six phases that it follows before declaring a pandemic<11>. Phase 1 represents a low risk and phase 6 is a full-blown pandemic, you can see the phases below:

Phase 1 - a virus is seen in animals but has not been shown to infections in humansPhase 2 - a known animal virus has caused an infection in humansPhase 3 - scattered or isolated incidence of cases or small clusters of the disease occurring in humans; possible cases of human-to-human transmission but not at a level to cause community-level outbreaksPhase 4 - human to human transmission at a rate that causes an outbreak in communitiesPhase 5 - the spread of the disease between humans is now evident in more than one countryPhase 6 - community-level outbreaks are in at least one additional country other than that seen in phase 5.

Once Phase 6 is reached preparation is then made for a global pandemic. Each phase has a list of actions that need to be followed to facilitate transparency and the education of health organisations and members of the public. The table below describes these actions.



It is important to try to prevent an epidemic from developing into a pandemic. This requires organisations and nations to act early and be prepared. A set of policies to try to limit the spread of an infectious agent beyond the initial individual cases and small clusters of infection are termed Containment. There are several measures that have proven effective in the control and containment of viruses<12>:

Controls - application of border controls to limit/prevent movement of individuals to and from affected areasIdentify cases - educate the public on the symptoms and risk factors, provide easy access to testing, flag potential cases in any healthcare encounters, track contact with infected individualsTrace contacts - a labour-intensive process which tracks an infected individual"s movements from the moment of infection to identify all individuals who have been potentially infected.

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Quarantine - separate an individual suspected of infection from contact with others for a certain period of time that covers the period of incubation for the diseaseIsolate - separate an individual who has been identified as infected from contact with others

Summarised by Tomas Pueyo as “very quickly limit people coming in, identify the sick, immediately isolate them, use heavy protective gear to protect their health workers, track all their contacts, quarantine them…”<13>

Managing a Pandemic

Once a pandemic is identified it is vital to take the appropriate action to contain, manage and reduce the spread of the virus. The key message at this stage is to reduce the transmission rate - the number of individuals infected by each single infected individual. If on average across a population the transmission rate is greater than one the number of cases will continue to increase. Measures that reduce the transmission rate to less than one will result in a decline in the total number of infections.

Once a significant level of infection is present within a population then reducing this rate of spread becomes vital. Actions targeted at reducing the transmission rate are termed Mitigation and can involve:

Economic measures - to provide relief to individuals and businesses and to increase compliance with social distancing related policies

All these measures aim to limit the population exposed to infection and to reduce the transmission rate between them. This results in a flattening of the curve of cases over time (see figures below) and so reducing the peak in the number of cases needing medical care. This maintains the ability of the healthcare system to provide quality care to those affected and reduce the mortality rate as far as possible. The greater the stress on the healthcare system the higher the likely mortality rate, as resources are unable to meet the demand and healthcare workers themselves exceed their capacity to provide care. Flattening the curve also extends the time scale of the epidemic so that any potential vaccine can at some future point be used to rapidly increase immunity within the population.