Defination of endemic epidemic and pandamic and sporadic from lark spm

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All four definitions are found directly from Park's Textbook of Preventive and Social Medicine. Here is the complete answer:

Epidemic, Endemic, Pandemic & Sporadic

Source: Park's Textbook of Preventive and Social Medicine (Lark's SPM)

1. EPIDEMIC

(Epi = upon; demos = people)

The occurrence in a community or region of cases of an illness, specific health-related behaviour, or other health-related events clearly in excess of normal expectancy. The community or region and the period in which the cases occur must be specified precisely. The number of cases indicating the presence of an epidemic varies according to:

The agent
Size and type of population exposed
Previous experience or lack of exposure to the disease
Time and place of occurrence

Epidemicity is thus relative to the usual frequency of the disease in the same area, among the specified population, at the same season of the year.

A single case of a communicable disease long absent from a population, or first invasion by a disease not previously recognized in that area, requires immediate reporting and full field investigation; two cases of such a disease associated in time and place may be sufficient evidence to be considered an epidemic.

2. ENDEMIC

(En = in; demos = people)

Refers to the constant presence of a disease or infectious agent within a given geographic area or population group, without importation from outside. May also refer to the "usual" or expected frequency of the disease within such an area or population group.

Example: Common cold is endemic because somebody always has one.

Related terms:

Hyperendemic: Disease constantly present at a high incidence/prevalence rate and affects all age groups equally.
Holoendemic: High level of infection beginning early in life and affecting most of the child population, with adults showing the disease less commonly than children (e.g., malaria).

An endemic disease, when conditions are favourable, may burst into an epidemic (e.g., hepatitis A, typhoid fever).

3. SPORADIC

The word sporadic means "scattered about." The cases occur irregularly, haphazardly from time to time, and generally infrequently. The cases are so few and separated widely in space and time that they show little or no connection with each other, nor a recognizable common source of infection.

Examples: Tetanus, herpes zoster, meningococcal meningitis.

A sporadic disease may be the starting point of an epidemic when conditions are favourable for its spread. Many zoonotic diseases are characterized by sporadic transmission to man.

4. PANDEMIC

An epidemic occurring over a very wide area, crossing international boundaries, and usually affecting a large number of people. Only some pandemics cause severe disease in individuals or at a population level.

Characteristics of an infectious agent that influence pandemic causation:

The agent must be able to infect humans
The agent must be able to cause disease in humans
The agent must spread easily from human to human

Examples: Influenza pandemics, cholera pandemics.

Summary Table

Term	Geographic Scope	Frequency	Key Feature
Sporadic	Local, scattered	Rare, infrequent	No common source or connection
Endemic	Fixed geographic area	Constant/usual	Expected baseline level
Epidemic	Community/region	Excess of expectancy	Clearly above normal
Pandemic	International/global	Large numbers	Crosses international boundaries

- Park's Textbook of Preventive and Social Medicine, p. 105-106

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