Intro to epidemiology

• 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 the human community
• Epidemic


  An increase in the frequency (incidence) of a disease above the usual and expected rate, which is called the endemic rate
• Notifiable disease surveillance made by the government before many people start dying
• Epidemiology


  Studies the patterns of disease occurrence in human populations and the factors that influence this pattern
• John Snow is considered the father of modern epidemiology and studied cholera
• Typical Epidemiologic Investigation

  Outbreak of hepatitis and Food poisoning
• Agent Factors of Disease

  Agent is any element, substance, or force, living or non-living, that can initiate or perpetuate a disease process
• Epidemiology


  Studies the factors contributing to the causation and behavior of any disease or event: AGENT, HOST, ENVIRONMENT
• 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
• Epidemic


  When epidemiologists detect the sign of an epidemic, they ask who, when, and where questions to understand the disease occurrence
• 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
• The ultimate goal of Epidemiology is to control and prevent the spread of disease
• Types of Agents

  • Living or non-living things, physical or mechanical in nature 2. Chemicals - endogenous or exogenous
• Main areas of investigation in Epidemiology


  Describing the distribution of health status in terms of various factors 2. Studying patterns of disease distribution in terms of causal factors
• The timely reporting of cases of notifiable disease allows public health authorities to detect an emerging epidemic at an early stage
• Uses of Epidemiology include studying the history of the health population, diagnosing the health of the community, improving health services, estimating disease risks, understanding chronic diseases, and searching for causes of health and diseases
• Characteristics of Agent of disease

  • Inherent characteristics- physical feature, biological requirement, chemical composition, resistance
  • Characteristic in relation to the environment- refers to the reservoir and source of infection and modes of transmission
  • Characteristic directly related to man: Infectivity, Pathogenicity, Virulence, Antigenicity
• The Host Factor of Disease

  • Age
  • Sex
  • Race
  • Habits, Customs, and religions
  • Exposure to agent
  • Defense mechanism of the host: Humoral defense, Cellular defense
• Incubation Period is the time between exposure to infectious agents up to the time of appearance of the earliest signs and symptoms
• Isolation and Quarantine

  Isolation- 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 infection
• Types of Agent

  • Living or non-living things
  • Physical or mechanical in nature such as extremes of temperature, light, electricity
  • Chemicals - endogenous (within the body) or exogenous (poison)
• Environmental Factors of Disease

  • Environment- sum total of an organism’s external surrounding conditions and influences that affect its life and development
  • Physical Environment, climate, Geography and location
  • Biologic Environment- living environment of man consisting of plants, animals, and fellow human beings
• Incubation Period

  1. Clinical incubation period- the time between exposure to a pathogenic organism and the onset of symptoms of a disease

  2. Biological Incubation Period- The time taken by the parasite to complete its development in the definite host
• Modes of Transmission

  1. Direct transmission- immediate transfer of infectious agent to a receptive portal of entry

  2. Indirect transmission: Vehicle-borne, Vector-borne, Mechanical vector, Biological vector

  3. Airborne- dissemination of microbial aerosols to a suitable portal of entry usually the respiratory tract
• Phases

  1. Pre-pathogenesis

  2. Pathogenesis
• Quarantine


  Restriction of the activities of well persons or animals exposed to a communicable disease during its period of communicability to prevent disease transmission during the incubation of infection
• Isolation


  Separation for the period of communicability, of infected persons or animals from others to prevent or limit the transmission of the infectious agent
• Pathogenesis includes the successful invasion and establishment of the agent in the host
• Requirements for the successful invasion of the host by an infectious agent

  1. Condition in the environment must be favorable to the agent or the agent must be able to adapt in the environment

  2. Suitable reservoirs must be present

  3. A susceptible host must be present

  4. Satisfactory portal of entry into the host

  5. Accessible portal of exit from the host

  6. Appropriate means of dissemination and transmission to a new host
• Categories of Quarantine

  • Absolute or Complete Quarantine
  • Modified Quarantine
• Categories of Isolation

  • Strict isolation
  • Contact isolation
  • Respiratory isolation
  • Tuberculosis isolation (AFB isolation)
  • Enteric Precautions
  • Drainage/secretion Precautions
  • Blood/body fluid Precautions
• Pre-pathogenesis is the phase before man is involved, where the agent interacts with the host and environmental factors before reaching man