chap 10

• Epidemiology


  The study of disease
• Epidemiologists


  • Study the factors that determine the frequency, distribution, and determinants of diseases in human populations
  • Develop ways to prevent, control, or eradicate diseases in populations
• Communicable disease


  An infectious disease that can be transmitted from one person to another
• Contagious disease


  A communicable disease that is easily transmitted from person-to-person
• Zoonotic diseases


  Diseases that humans acquire from animal sources
• Incidence


  The number of new cases of a particular disease in a defined population during a specific time period
• Morbidity rate


  The same as incidence, but usually expressed per 1,000, 10,000 or 100,000 population
• Period prevalence


  The number of cases of a disease existing in a given population during a specific time period (e.g., during the year 2009)
• Point prevalence


  The number of cases of a disease existing in a given population at a particular moment in time (e.g., right now)
• Mortality/death rate


  The ratio of the number of people who died of a particular disease during a specified time period per a specified population
• Sporadic disease


  A disease that occurs only occasionally within the population of a particular geographic area
• Endemic disease


  A disease that is always present within the population of a particular geographic area
• Epidemic disease


  A greater than usual number of cases of a disease in a particular region, usually within a short period of time
• Pandemic


  A disease that is occurring in epidemic proportions in many countries simultaneously
• Examples of pandemics


  • Spanish flu pandemic of 1918
  • H1N1 ("swine flu") pandemic of 2009-2010
  • HIV/AIDS
  • Tuberculosis
  • Malaria
• Factors determining whether an infectious disease occurs

  • Factors relating to the pathogen (e.g., virulence, mode of entry, number of organisms)
  • Factors relating to the host (e.g., health status, nutritional status, hygiene, age, travel, lifestyle)
  • Factors relating to the environment (e.g., physical factors such as climate, season, geographic location; availability of appropriate reservoirs; sanitary and housing conditions; and availability of clean water)
• Components in the infectious disease process

  • A pathogen
  • A source of the pathogen (a reservoir)
  • A portal of exit
  • A mode of transmission
  • A portal of entry
  • A susceptible host
• Living reservoirs of infection

  • Humans
  • Pets
  • Farm animals
  • Insects
  • Arachnids
• Types of human carriers

  • Passive carriers
  • Incubatory carriers
  • Convalescent carriers
  • Active carriers (completely recovered from disease but still carry the pathogen for a long time)
• Zoonoses


  Infectious diseases that humans acquire from animal sources
• Examples of zoonotic diseases

  • Rabies
  • Lyme disease
• Arthropod vectors


  Arthropods (insects and arachnids) that transmit infectious diseases
• Examples of arthropod-borne diseases

  • Lyme disease
  • Malaria
• Fomites


  Inanimate objects capable of transmitting pathogens
• Most common modes of transmission of infectious diseases

  • Direct skin-to-skin contact
  • Direct mucous membrane-to-mucous membrane contact by kissing or sexual intercourse
  • Indirect contact via airborne droplets of respiratory secretions
  • Indirect contact via food and water contaminated by fecal matter
  • Indirect contact via arthropod vectors
  • Indirect contact via fomites
  • Indirect contact via transfusion of contaminated blood or blood products or by parenteral injection using nonsterile syringes or needles
• World Health Organization (WHO)

  • A specialized agency of the United Nations founded in 1948
  • Missions: to promote technical cooperation for health among nations; to carry out programs to control and eradicate diseases; to improve the quality of human life
  • Eradicated smallpox
  • Investigates outbreaks of Ebola virus
  • Attempting to eradicate polio and guinea worm disease
• Measures for prevention and control of epidemics


  • Increase host resistance through development and administration of vaccines
  • Ensure protection of exposed persons (passive immunization)
  • Segregate, isolate and treat those with contagious infections
  • Identify and control potential reservoirs and vectors of infectious diseases
• Biological warfare agents


  Microbes purposely used to harm others in wartime
• Bioterrorism agents


  Pathogens used to create fear, chaos, illness, and death in situations other than war
• Examples of biological warfare/bioterrorism agents


  • Bacillus anthracis (the cause of anthrax)
  • Clostridium botulinum (the cause of botulism)
  • Smallpox virus (Variola major)
• Epidemiology


  The study of disease
• Epidemiologists


  • Study the factors that determine the frequency, distribution, and determinants of diseases in human populations
  • Develop ways to prevent, control, or eradicate diseases in populations
• Communicable disease


  An infectious disease that can be transmitted from one person to another
• Contagious disease


  A communicable disease that is easily transmitted from person-to-person
• Zoonotic diseases


  Diseases that humans acquire from animal sources
• Incidence


  The number of new cases of a particular disease in a defined population during a specific time period
• Morbidity rate


  The same as incidence but usually expressed per 1,000, 10,000 or 100,000 population
• Period prevalence


  The number of cases of a disease existing in a given population during a specific time period (e.g., during the year 2009)
• Point prevalence


  The number of cases of a disease existing in a given population at a particular moment in time (e.g., right now)
• Mortality/death rate


  The ratio of the number of people who died of a particular disease during a specified time period per a specified population