Epidemiology

•  Study the occurrence and distribution of diseases as well as distribution of determinants of health state or events in specified population and the application of this study to control health problems

  Epidemiology
• • Field of science dealing with the relationship of the various factors which determine the frequencies and distribution of an infectious process. A disease or a physiological state in human community.

  Epidemiology
• • Study of the behavior of disease in the community rather than in individual patients and includes the study of reservoirs and sources of human disease.

  Epidemiology
• • Studies the patterns of disease occurrence in human populations and the factors that influence this pattern. The term obviously is related to the epidemic (derived from the Greek word” upon the people” meaning leading the people).

  Epidemiology
• C-E. A. Winslow, the great public health leader of the early 20th century, called epidemiology “the diagnostic discipline of public health.”
• Sporadic - refers to a disease that occurs infrequently and irregularly.
• Endemic - constant presence and/or usual prevalence of a disease infectious agent in a population within a geographic area.
• 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.
• Pandemic - refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people.
• Epidemic — an increase in the frequency (incidence) of a disease above the usual and expected rate, which is called the endemic rate., thus epidemiology counts cases of a disease, and when they detect the sign of epidemic, they ask who, when and where questions.
• Notifiable disease - surveillance made by the government before many people start dying. 

  • The timely reporting of cases of notifiable disease allows public health authorities to detect an emerging epidemic at an early stage.
  • A typical Epidemiologic Investigation - Outbreak of hepatitis and Food poisoning
• What is the Goal of epidemiology?

  The ultimate goal is to use this knowledge to control and prevent the spread of disease.
• Two main areas of investigation.

  • Describes the distribution of health status in terms of age, gender, race, geography, and time.
  • Patterns of disease distribution in terms of causal factor.
• In epidemiology of any disease or event, one studies the factor which contribute to its causation and behavior - agent, host, environment. 
• Epidemiology concept maintains that there can be no single cause of disease
• John Snow - father of modern epidemiology - Study about cholera.
• Agent is any element, substance or force whether living or non-living thing; the presence or absence can initiate or perpetuate a disease process.
• Inherent characteristics of infectious agents include physical features, biological requirements, chemical composition, and resistance
• Characteristics in relation to the environment include the reservoir and source of infection, as well as modes of transmission
• Characteristics directly related to man:

  • Infectivity: ability to gain access and adapt to the human host to the extent of finding lodgement and multiplication
  • Pathogenicity: measures the ability of the agent when lodged in the body to set up a specific reaction
  • Virulence: refers to the severity of the reaction produced and is usually measured in terms of fatality
  • Antigenicity: ability to stimulate the host to produce antibodies
• Direct transmission is the immediate transfer of an infectious agent to a receptive portal of entry
• Indirect transmission can occur through:

  • Vehicle-borne: contaminated inanimate objects or materials
  • Vector-borne: from other living organisms (e.g., insects)
  • Mechanical vector
  • Biological vector
• Airborne transmission involves the dissemination of microbial aerosols to a suitable portal of entry, usually the respiratory tract
• Droplet nuclei are usually small residues resulting from the evaporation of fluid from droplets emitted by an infected host
• Dust can also play a role in indirect transmission of infectious agents
• Host Factor of Disease

  1. Age
  2. Sex
  3. Race
  4. Habits, Customs and religions
  5. Exposure to agent
  6. Defense mechanism of the host
• Humoral defense - these are cells in our body like plasma cells and lymphocytes that produce antibodies to neutralize harmful effects of the infectious agents and body fluids in our body that possess substance that have antimicrobial properties
• Cellular defense - there are cells in our body like macrophages and neutrophils involved in the process of phagocytosis
• Environment is the sum total of an organism’s external surrounding conditions and influences that affect its life and development
• In the physical environment, climate plays a role as certain diseases have seasonal distribution
• Geography and location are factors that influence the spread and prevalence of diseases
• The biologic environment, the living environment of man, consists of plants, animals, and fellow human beings
• Incubation Period - Time between exposure to infectious agent up to the time of appearance of the earliest signs and symptoms
• Clinical incubation period - the time between exposure to a pathogenic organism and the onset of symptoms of a disease.
• Biological Incubation Period - The time taken by the parasite to complete its development in the definite host (from the time of entry of the infective larvae to the presence of microfilariae) is called the Intrinsic incubation period (Biological incubation).
• Isolation - As applied to patient, separation for the period of communicability, of infected persons or animals from others in such places and under such conditions as to prevent or limit the effect of the direct or indirect transmission of the infectious agent from those infected to those who are susceptible or who may spread the disease agent.
• Strict isolation is designed to prevent transmission of highly contagious or virulent infectious diseases that may spread by direct contact or droplet
• Contact isolation is for less highly transmissible or serious infections, for diseases or conditions which are spread primarily by close or direct contact
• Respiratory isolation aims to prevent transmission of infectious diseases over short distances through the air
• Tuberculosis isolation (AFB isolation) is for patients with pulmonary tuberculosis who have a positive sputum smear or chest x-rays strongly suggesting active tuberculosis