General Concepts in Epidemiology

General Concepts in Epidemiology

• Epidemiology studies the distribution and determinants of diseases in populations.
• Classical epidemiology focuses on disease distribution and its causes within populations.
• Clinical epidemiology applies epidemiological principles to enhance disease prevention, detection, and treatment in patients.
• Descriptive studies examine individual characteristics, locations, and timing of events relative to a health outcome.
• Analytical studies aim to determine how an exposure influences a particular outcome.

Scope of Epidemiology

• Originally, it addressed epidemics of communicable diseases.
• Later, it broadened to include endemic communicable and non-communicable diseases.
• Now, it applies to all diseases and health-related events.

Endemic

• A disease consistently present at an expected rate within a specific population or region.
• Time and area are unlimited.
• Examples include malaria in Africa, yellow fever in South America and Africa, and Hepatitis C in Egypt.
• Possible factors include disease vectors and pathogen reservoirs.
• Geographic and climatic conditions and living condition like housing, sewage disposal are other factors

Epidemic

• A disease affecting individuals at an unusually fast or unexpected rate within a specific population or region, in a limited time and area .
• Examples include the Ebola fever epidemic in West Africa (2014) and seasonal influenza.
• Possible factors include increased pathogen infectivity, living conditions (crowded areas), and spread to new geographical areas.

Pandemic

• A worldwide epidemic with unlimited area, but limited time.
• Examples include the Spanish flu (1918/1919) and Covid-19.
• Factors include global trade, travel, and increased pathogen infectivity (antigenic shift).

Important Terms

• Infection: Successful entry, development, or multiplication of pathogenic organisms in a living being's body, which may or may not lead to disease.
• Subclinical Infection: An infection insufficient to cause disease, where the individual may or may not transmit the disease.
• Cross-infection: Infection spreads between people, animals, or from animals to people and vice versa.
• Opportunistic Infection: Infections caused by organisms exploiting a host's weakened immune system, common in AIDS, e.g., Mycobacterium tuberculosis, Cytomegalovirus.
• Contamination: The presence of infectious organisms on inanimate objects, making them impure.
• Pollution: Presence of offensive matter in the environment, like air pollution
• Host: A person or an animal, including birds and arthropods, that affords lodgement to an infectious agent or a parasite
• Vector: An arthropod that spreads disease from person to person, such as houseflies, lice, and mosquitoes.
• Exotic Disease: A disease imported to a country where it does not exist, e.g., yellow fever in India, rabies in UK.
• Zoonotic Disease (Zoonosis): Disease naturally transmitted between vertebrate animals and humans.
• Iatrogenic Disease: Disease induced by a medical intervention, unintentional and accidental, e.g., reaction to penicillin, hepatitis B following blood transfusion.
• Eradication of a Disease: Complete removal of the causative agent, eliminating the disease and the risk of infection without immunization; for example, smallpox.
• Elimination of a Disease: Reducing disease incidence to a low level where it is no longer a public health problem; neonatal tetanus and leprosy are examples, Tetanus cannot be eradicated because the spores of Clostridium tetani cannot be removed from the nature.
• Incubation Period: The period between pathogen entry and the appearance of the first clinical signs or symptoms in an individual.
• Latent Period: For non-communicable diseases, it is the period between start of pathology and the appearance of the first clinical sign or symptom of the disease’
• Surveillance: Collection of reliable information about status of a specific disease in the given population and the factors related to it , for monitoring and reporting on trends in specific health problems for prevention and control of that health problem/ disease