The World Health Organisation (WHO) said on February 4 that the outbreak of the deadly novel coronavirus, which has spread from China to two dozen countries, does not yet constitute a “pandemic”.

“Currently we are not in a pandemic,” said Sylvie Briand, head of WHO’s Global Infectious Hazard Preparedness division. Instead, she said, “we are at the phase where it is an epidemic with multiple foci”.

Epidemiology

Epidemiology is the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems.

Various methods can be used to carry out epidemiological investigations: surveillance and descriptive studies can be used to study distribution. Analytical studies are used to study determinants.

A pandemic is the highest possible level of disease, or a measure of how many people have gotten sick from a particular disease and how far it has spread - but before a common illness reaches pandemic proportions, it has to exceed a few other levels, according to the Centers for Disease Control and Prevention.

Different levels of diseases

Endemic: It refers to the constant presence and / or usual prevalence of a disease or infectious agent in a population within a geographic area. For example, malaria is endemic to some regions.

The amount of a particular disease that is usually present in a community is referred to as the baseline or endemic level of the disease. This level is not necessarily the desired level, which may in fact be zero, but rather is the observed level.

In the absence of intervention and assuming that the level is not high enough to deplete the pool of susceptible persons, the disease may continue to occur at this level indefinitely. Thus, the baseline level is often regarded as the expected level of the disease.

Hyperendemic refers to persistent, high levels of disease occurrence.

Sporadic: It refers to a disease that occurs infrequently and irregularly. Examples of sporadic diseases include tetanus, rabies and plague.

Epidemic: Occasionally, the amount of disease in a community rises above the expected level. Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area. Influenza is a good example of a commonly epidemic disease.

Outbreak: It  carries the same definition of epidemic, but is often used for a more limited geographic area.

Pandemic: It refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people. For example, HIV / AIDS is a pandemic disease and novel influenza virus strains often become pandemic.

In 2005, WHO released a six-stage classification that describes the process by which influenza virus moves from the first few infections in humans through to a pandemic.

Interpandemic Period

Phase 1: No new influenza virus subtypes have been detected in humans. An influenza virus subtype that has caused human infection may be present in animals. If present in animals, the risk of human infection or disease is considered to be low.

Phase 2: No new influenza virus subtypes have been detected in humans. However, a circulating animal influenza subtype poses a substantial risk of human disease.

Pandemic Alert Period

Phase 3: Human infection(s) with a new subtype, but no human-to-human spread, or at most rare instances of spread to a close contact.

Phase 4: Small cluster(s) with limited human-to-human transmission but spread is highly localised, suggesting that the virus is not well adapted to humans.

Phase 5: Larger cluster(s) but human-to-human spread still localised, suggesting that the virus is becoming increasingly better adapted to humans, but may not yet be fully transmissible (substantial pandemic risk).

Pandemic Period

Phase 6: Increased and sustained transmission in general population.

Major pandemics

Spanish Flu

The 1918 influenza pandemic (also known as Spanish Flu) was the most severe pandemic in recent history. It was caused by an H1N1 virus with genes of avian origin. Although there is not universal consensus regarding where the virus originated, it spread worldwide during 1918-19. The number of deaths was estimated to be at least 50 million worldwide.

Asian Flu

In February 1957, a new influenza A (H2N2) virus emerged in East Asia, triggering a pandemic (Asian Flu). It was first reported in Singapore in February 1957, Hong Kong in April 1957 and in coastal cities in the US in summer 1957. The estimated number of deaths was 1.1 million worldwide.

Hong Kong Flu

The 1968 pandemic was caused by an influenza A (H3N2) virus. Because it originated in Hong Kong, the pandemic is also referred to as Hong Kong Flu. The estimated number of deaths was 1 million worldwide. Most excess deaths were in people 65 years and older.

H1N1

In the spring of 2009, a novel influenza A (H1N1) virus emerged. It was detected first in the US and spread quickly across the world. By the time WHO declared a pandemic in June 2009, a total of 74 countries and territories had reported laboratory confirmed infections.

Manorama Yearbook app is now available on Google Play Store and iOS App Store