PPT 4

• Epidemiology


  The study of factors that determine the frequency, distribution and determinants of diseases in human populations and ways to prevent, control or eradicate diseases in populations
• Factors affecting infectious disease include lack of immunizations, nutritional status, inadequate sanitation procedures, locations (reservoirs) where pathogens are lurking, and the various ways in which infectious diseases are transmitted

  
• Epidemiologists


  • Scientists who specialize in the study of disease and injury patterns (incidence and distribution patterns) in populations and ways to prevent or control diseases and injuries
  • Study virtually all types of diseases, including heart, hereditary, communicable, and zoonotic diseases and cancer
• Communicable disease


  An infectious disease that is transmissible from one person to another

  
• Contagious disease


  A communicable disease that is easily transmitted from one person to another

  
• Communicable diseases


  • Gonorrhea
  • Influenza
• Zoonotic disease


  Infectious diseases 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


  The number of cases of a disease existing in a given population during a specific time period
• Point prevalence


  The number of cases of a 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 (sporadically) within the population of a particular geographic area
• Sporadic diseases


  • Cholera
  • Tetanus
  • Typhoid fever
• Epidemic disease


  A disease that occurs in a greater than usual number of cases in a particular region and usually occurs within a relatively short period of time
• Epidemic diseases


  • Staphylococcal food poisoning
• Endemic disease


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


  • Bacterial diseases such as tuberculosis (TB)
  • Staphylococcal and streptococcal infections
  • Sexually transmitted diseases (STDs) such as gonorrhea

  
• Pandemic disease


  A disease that is occurring in epidemic proportions in many countries simultaneously, sometimes worldwide
• Pandemic diseases


  • HIV/AIDS
  • Tuberculosis
  • Malaria
  • COVID-19
• HIV infection in humans can be traced to an African serum sample collected in 1959, and it is possible that humans were infected with HIV before that date

  
• HIV, the virus that causes AIDS, was discovered in 1983 and is thought to have been transferred to humans from other primates

  
• Many strains of Mycobacterium tuberculosis (the bacterium that causes TB) have developed resistance to the drugs used to treat TB, resulting in multidrug-resistant tuberculosis (MDR-TB) or extensively drug-resistant tuberculosis (XDR-TB)
• Malaria is the fifth leading cause of death from infectious diseases worldwide
• Factors pertaining to the pathogen

  • Virulence of the pathogen
  • A way for the pathogen to enter the body
  • The number of organisms that enter the body

  
• Factors pertaining to the host

  • The person's health status
  • The person's nutritional status
  • Other factors pertaining to the susceptibility of the host
• Factors pertaining to the environment

  • Physical factors such as geographic location, climate, heat, cold, humidity, and season of the year
  • Availability of appropriate reservoirs, intermediate host and vectors
  • Sanitary and housing conditions; adequate waste disposal; adequate health care
  • Availability of potable (drinkable) water
• Components of the chain of infection

  • Pathogen
  • Reservoir
  • Portal of exit
  • Mode of transmission
  • Portal of entry
  • Susceptible host

  
• Strategies for breaking the chain of infection

  • Eliminate or contain the reservoirs of pathogens or curtail the persistence of a pathogen at the source
  • Prevent contact with infectious substances from exit pathways
  • Eliminate means of transmission
  • Block exposure to entry pathways
  • Reduce or eliminate the susceptibility of potential hosts
• Specific methods of breaking the chain of infection

  • Practicing effective hand hygiene procedures
  • Maintaining good nutrition and adequate rest and reduce stress
  • Obtaining immunizations against common pathogens
  • Practicing insect and rodent control measures
  • Practicing proper patient isolation procedures
  • Ensuring proper decontamination of surfaces and medical instruments
  • Disposing sharps and infectious wastes properly
  • Using gloves, gowns, masks, respirators, and other personal protective equipment, whenever appropriate to do so
  • Using needle safety devices during blood collection
• Living reservoirs of infection

  • Human carriers (passive, incubatory, convalescent, active)
  • Animals (zoonotic diseases)
  • Arthropods (vectors)
• Non-living reservoirs of infection

  • Air
  • Dust
  • Food and milk
  • Human and animal fecal matter
  • Fomites
• Modes of transmission


  Contact (direct or indirect), droplet, airborne, vehicular, and vector transmission
• Dust particles can carry spores of certain bacteria and dried bits of human and animal excretions containing pathogens

  • Histoplasmosis
• Food and milk may be contaminated by careless handling, which allows pathogens to enter from soil, dust particles, dirty hands, hair, and respiratory secretions

  • Botulism
• If these pathogens are not destroyed by proper processing and cooking, food poisoning can develop
• Human and animal fecal matter from outhouses, cesspools, and feed lots is often carried into water supplies
• Fomites


  Inanimate objects capable of transmitting pathogens
• Fomites found within healthcare settings

  • Patients' gowns
  • Bedding
  • Towels
  • Eating and drinking utensils
  • Hospital equipment, such as bedpans, stethoscopes
• Modes of transmission


  • Contact (either direct or indirect)
  • Droplet
  • Airborne
  • Vehicular
  • Vector transmission