CPH LEC | EPIDEMIOLOGY

• Epidemiology


  A science concerned with the various factors and conditions which influence the occurrence and distribution of health, disease, defect, disability and health among a group of individuals
• Epidemiology


  • Its methods are applicable to problems other than those of health and disease
  • Includes studies of all conditions and circumstances important to man's health e.g. accidents, suicides, medical care, diseases, and administrative problems, etc.
• 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
• 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 diseases
• Two main areas of investigation in epidemiology

  • Describes the distribution of health status in terms of age, gender, race, geography and time
  • Patterns of disease distribution in terms of causal factor
• Agent


  Any element, substance or force whether living or nonliving; the presence or absence can initiate or perpetuate a disease process
• Types of Agent


  • Living or non-living, physical or mechanical in nature such as extremes of temperature, light, electricity
  • Chemicals - endogenous (within the body) or exogenous (poison)
• Characteristics of Agents 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
• Modes of Transmission


  • Direct Transmission - immediate transfer of infectious agent to a receptive portal of entry
  • Indirect transmission: Vehicle-borne - contaminated inanimate objects or material, Vector-borne - from other living organisms
  • Airborne - dissemination of microbial aerosols to a suitable portal of entry usually the respiratory tract
• Portal of Entry Modes of Transmission

  • Mouth - Ingestion, Kissing
  • Skin - Skin penetration, injection, bite of arthropod
  • Nose - Inhalation
  • Genitals - Sexual Intercourse
• Host Factors of Disease

  • Age
  • Sex
  • Race
  • Habits, customs and religion
  • Exposure to agent
  • Defense mechanism of the host: Humoral defense, Cellular defense
• Immunity


  The total property of an individual to protect himself from an infectious agent
• Types of Immunity


  • Non specific resistance - present at the time of birth or has developed during maturation
  • Specific resistance - acquired as a result of prior exposure with a foreign substance
• Types of Specific Resistance


  • Active - when what has been introduced to the individual is the antigen, and the body makes the antibody
  • Passive - when what has been introduced to the body is already antibodies that provide immediate protection against microorganisms
• Environmental Factors of Disease

  • Physical Environment: Climate, Geography and location
  • Biologic Environment - living environment of man consists of plants, animals and fellow human beings
  • Socio-economic Environment
• Disease Causation


  The occurrence of disease follows biologic laws which apply to both communicable and non communicable diseases: 1) Disease results from imbalance between the forces of the agent and host, 2) The nature and extent of imbalance depends on the nature and characteristics of host and agent, 3) The characteristics of two are influenced considerably by the condition of the environment
• Incubation Period


  Time between exposure to infectious agents up to the time the earliest signs and symptoms appear
• Types of Incubation Period

  • Clinical Incubation Period
  • Biological Incubation Period
• 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 infectious agent from those infected to those who are susceptible or who may spread the disease agent
• Categories of Isolation


  • Strict Isolation - for highly contagious or virulent infections that may spread by both air and contact
  • Contact Isolation - for less highly transmissible or serious infections, for disease or conditions which are spread primarily by close or direct contact
  • Respiratory Isolation - to prevent transmission of infectious diseases over short distances through the air
  • Tuberculosis Isolation (AFB Isolation) - for patients with pulmonary tuberculosis who have a positive sputum smear
• Clinical Incubation Period


  The period between exposure to an infectious agent and the appearance of symptoms
• Biological Incubation Period


  The period between exposure to an infectious agent and the ability of the agent to be transmitted to others
• Categories of Isolation


  • Strict Isolation
  • Contact Isolation
  • Respiratory Isolation
  • Tuberculosis Isolation (AFB Isolation)
  • Enteric Precautions
  • Drainage/secretion Precautions
  • Blood/body fluid Precautions
• Recommended isolation practice for admitted infectious diseases

  • AIDS: Blood/body fluid Precaution
  • Chicken pox: Drainage/secretion Precaution
  • Cholera: Enteric Precaution
  • Dengue: No isolation
  • Diarrhea: Enteric Precaution
  • Diphtheria: Strict Isolation
  • German Measles: Contact Isolation
  • Hepatitis A: Enteric Precaution
  • Leptospirosis: Blood/body Fluid Precaution
  • Malaria: Blood Precaution
  • Pertussis: Respiratory Precaution
  • Poliomyelitis: Enteric Precaution
  • SARS: Strict Isolation
  • Typhoid: Enteric Precaution
• Quarantine


  Restriction of the activities of a well persons or animals who have been exposed to a case of communicable diseases during its period of communicability to prevent disease transmission during incubation period if infection should occur
• Categories of Quarantine


  • Absolute or Complete Quarantine
  • Modified Quarantine
• Pre-pathogenesis


  The phase before man is involved, where the interaction of the agent, the host and environment factors leads the agent to finally reach man
• Pathogenesis


  The phase that includes the successful invasion and establishment of the agent in the host, after a period of incubation where the agent multiplies and develops, or gets absorbed and fixed in the tissues, leading to detectable evidence of the disease process in man
• Requirements for the successful invasion of the host by an infectious agent

  • Condition in the environment must be favorable to the agent or the agent must be able to adopt to the environment
  • Suitable reservoirs must be present
  • A susceptible host must be present
  • Satisfactory portal of entry into the host
  • Accessible portal of exit from the host
  • Appropriate means of dissemination and transmission to a new host
• Agent


  Any element, substance, or force whether living or non- living, the presence or absence of which can initiate or perpetuate a disease process
• Types of Agents


  • Non-living
  • Living
  • Borderline
• Examples of living agents

  • Plants (bacteria, fungi, molds, yeasts)
  • Animals (big ones like animals of prey and arthropods, multicellular types like flatworms and roundworms, unicellular types like amoeboid protozoa, ciliated protozoa, flagellated protozoa, blood parasites)
• Characteristics of agents of diseases

  • Inherent characteristics (physical features, biologic requirements, chemical make-up, viability and resistance)
  • Characteristics directly inherent to man
  • Characteristics related to the environment
• Pathogenicity


  The ability of an agent when lodged in the body to set up a specific reaction, local or general, clinical or subclinical
• Virulence


  The severity of the reaction produced, usually measured in terms of fatality
• Antigenicity


  The ability to stimulate the host to produce antibodies