chap 11

• Epidemiology


  The study of disease
• Epidemiologists


  • Study the factors that determinants of diseases in human populations
  • Develop ways to prevent, control or eradicate disease in populations
• Epidemiologic terminology


  • Communicable diseases
  • Contagious diseases
  • Zoonotic diseases
  • Incidence
  • Morbidity rate
  • Prevalence
  • Mortality rate
  • Sporadic diseases
  • Endemic diseases
  • Epidemic diseases
  • Pandemic diseases

  
• 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 disease


  A disease that humans acquire from animal sources
• Incidence


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


  The number of new cases of a particular disease that occurred during a specified time period per a specifically defined population
• Prevalence


  • Period prevalence is the number of cases of the disease existing in a given population during a specific time period
  • Point prevalence is the number of cases of the disease existing in a given population at a particular moment in time
• Mortality 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


  • Influenza (Spanish Flu 1918)
  • HIV/AIDS
  • Tuberculosis
  • Malaria
• Factors determining whether an infectious disease occurs

  • Factors pertaining to the pathogen
  • Factors pertaining to the host
  • Factors pertaining to the environment

  
• Chain of infection


  1. Pathogen

  2. Source of pathogen (reservoir)

  3. Portal of exit

  4. Mode of transmission

  5. Portal of entry

  6. Susceptible host

  
• Living reservoirs of infection

  • Human carriers
  • Animals
  • Arthropods
• Human carriers


  • Passive carriers
  • Incubatory carriers
  • Convalescent carriers
  • Active carriers
• Zoonotic diseases


  Infectious diseases that humans acquire from animal sources
• Arthropod vectors


  Arthropods involved in the transmission of infectious diseases
• Non-living reservoirs of infection

  • Air
  • Soil
  • Dust
  • Contaminated water and foods
  • Insects
  • Infected humans
  • Fomites

  
• Fomites


  Inanimate objects capable of transmitting pathogens

  
• Modes of disease transmission

  • Direct skin-to-skin contact
  • Direct mucous membrane-to-mucous membrane contact
  • Airborne droplets of respiratory secretions
  • Contamination of food and water by fecal matter
  • Arthropod vectors
  • Contaminated fomites
  • Transfusion of contaminated blood or blood products
  • Parenteral injection using nonsterile syringes or needles

  
• World Health Organization (WHO)

  • A specialized agency of United Nations founded in 1948
  • Mission: to promote technical cooperation for health among nations, carry out programs to control and eradicate disease and improve the quality of human life
  • Investigates outbreaks of Ebola virus
  • Eradicated smallpox
  • Attempting to eradicate polio and dracunculiasis
• Centers for Disease Control and Prevention (CDC)


  • A federal agency administered by the U.S. Department of Health and Human Services, Atlanta, GA. Established in 1946
  • Mission: to promote health and quality of life by preventing and controlling diseases, injury, and disability
  • Certain infectious diseases, known as nationally notifiable diseases must be reported to the CDC
  • Publishes Morbidity and Mortality Weekly Report (MMWR)
• Measures for prevention and control of epidemics

  • Increase host resistance through vaccines
  • Ensure protection for those exposed to a pathogen
  • Segregate, isolate and treat those with contagious infections
  • Identify and control potential reservoirs and vectors of infectious diseases
• Bioterrorism and biological warfare agents

  • Bacillus antracis (anthrax)
  • Clostridium botulinum (botulism)
  • Smallpox virus (Variola major)
  • Yersinia pestis (plague)
• Microbes purposely used to harm others in wartime are called biological warfare (bw) agents
• Pathogens used to create fear, chaos, illness and death are called bioterrorism agents
• Sources of water contamination

  • Rainwater
  • Groundwater from wells

  
• Water treatment


  • Major steps: sedimentation, coagulation, filtration and chlorination
  • Water is tested for contamination by checking for the presence of coliform bacteria

  
• Sewage treatment


  • Primary treatment
  • Secondary treatment
  • Tertiary treatment
• Raw sewage consists mainly of water, fecal material, garbage and bacteria