Epidemiology

• 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
• Epidemiologist


  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
• Epidemiology


  1. Systematic collection

  2. Analysis

  3. Interpretation of data

  
• Frequency


  The number of times an event occurs
• Distribution


  Distribution of an event by person, place and time
• Determinants


  Factors the presence/absence of which affect the occurrence and level of an event
• Epidemiology is not only the study of diseases, it studies all health related conditions
• John Snow


  • Discovered the cause of the cholera outbreak in London in 1854 and therefore also ending it, considered the founder of epidemiology
• Epidemiology tools


  • Incidence
  • Morbidity rate
  • Period prevalence
  • Point prevalence
  • Mortality rate
  • Case fatality rate
• Incidence


  The number of new cases of that 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 (usually per 1,000, 10,000, or 100,000 population)
• Period prevalence


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


  The number of cases of the disease existing in a given population at a particular moment in time
• Mortality


  Death
• Mortality rate


  The ratio of the number of people who died of a particular disease during a specified time period per a specified population (usually per 1,000, 10,000, or 100,000 population)
• In 2022, a total of 679,766 deaths were registered in the Philippines, a decrease of 22.7 percent from 879,429 in 2021. This is equivalent to a crude death rate of 6.1, or six deaths per 1,000 population in 2022. This corresponds to an average of 1,862 deaths per day, which translates to 78 deaths per hour or about 1 death per minute.
• Types of diseases according to transmissibility

  • Infectious diseases
  • Communicable disease
  • Contagious disease
  • Zoonotic diseases
• Infectious diseases


  Diseases caused by infectious agents such as viruses, bacteria, parasites, or fungi, that can often be spread from person to person via direct or indirect contact
• Infectious diseases


  • Tuberculosis
  • Malaria
  • HIV/AIDS
• Communicable diseases


  Illnesses that spread from one person to another or from an animal to a person, or from a surface or a food
• Contagious disease


  A communicable disease that can spread rapidly from person to person through direct contact, indirect contact, or droplet contact
• Top 5 contagious diseases

  • Influenza (flu)
  • Viral upper respiratory tract infections
  • COVID-19, other coronaviruses
  • Strep throat
  • Gastrointestinal illnesses
• Zoonotic diseases


  Infections that are spread between people and animals, caused by germs such as viruses, bacteria, parasites, and fungi
• Types of zoonotic diseases by etiology

  • Bacterial zoonoses (e.g. anthrax, salmonellosis, tuberculosis, Lyme disease, brucellosis, plague)
  • Viral zoonoses (e.g. rabies, AIDS, Ebola, avian influenza)
  • Parasitic zoonoses (e.g. trichinosis, toxoplasmosis)
• Types of diseases according to occurrence

  • Sporadic disease
  • Endemic diseases
  • Epidemic (or outbreak)
  • Pandemic
• Sporadic disease


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


  Diseases that are always present within the population of a particular geographic area, with the number of cases fluctuating over time
• Epidemic (or outbreak)


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


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


  • COVID-19
  • Tuberculosis
  • Malaria
• Factors pertaining to the pathogen

  • Virulence
  • Way of entry
  • Number of organisms that enter the body
• Factors pertaining to the host

  • The person's health status
  • The person's nutritional status
  • The susceptibility of the host (e.g., age, lifestyle, behavior, socioeconomic level, occupation, travel, hygiene, substance abuse, immune status, immunizations or previous experience with the pathogen)
• Factors pertaining to the environment

  • Physical factors (e.g. geographic location, climate, heat, cold, humidity, season)
  • Availability of appropriate reservoirs, intermediate hosts, and vectors
  • Sanitary and housing conditions; adequate waste disposal; adequate healthcare
  • Availability of potable (drinkable) water
• Links in the chain of infection

  • The Infectious Agent
  • The Reservoir Host
  • The Portal of Exit
  • The Route of Transmission
  • The Portal of Entry
  • The Susceptible Host
• Carrier Hosts


  Hosts that do not show any outward signs or symptoms of a disease but are still capable of transmitting the disease
• Routes of transmission


  • Airborne transmission
  • Contact transmission (direct, indirect, droplet spread)
  • Vehicular transmission
• Airborne transmission


  Occurs when fine microbial particles or dust particles containing microbes remain suspended in the air for a prolong period and spread by air current and inhaled
• Direct contact transmission


  Person to person transfer of organism through direct skin to skin contact or direct mucous membrane-to-mucous membrane contact
• Indirect contact transmission


  Occurs when the susceptible person comes in contact with a contaminated object
• Droplet spread


  Contact with respiratory secretions, when the infected person coughs, sneezes or talks. Microbes carried in droplets can travel up to 3 ft or 1 meter and settle on a surface.