Epidemiology and Public Health Microbiology

Fundamentals of Epidemiology

  • Epidemiology: The science evaluating the occurrence, determinants, distribution, and control of health and disease in defined human populations.
  • John Snow: Recognized as the first epidemiologist for his study of cholera in London.
  • Centers for Disease Control and Prevention (CDC): Based in Atlanta, GA; focuses on disease prevention, environmental health, and health education.
  • World Health Organization (WHO): The international counterpart located in Geneva, Switzerland.

Disease Frequency and Terminology

  • Sporadic disease: Occurs occasionally and at irregular intervals.
  • Endemic disease: Maintains a steady, low-level frequency at regular intervals.
  • Hyperendemic disease: Gradually increases above endemic levels but stays below epidemic levels.
  • Outbreak: A sudden, unexpected, and focal occurrence of disease.
  • Epidemic: A sudden increase in occurrence above expected levels; the index case is the first case in an epidemic.
  • Pandemic: An increase in disease occurrence in large populations across at least two countries.

Statistical Measures of Disease

  • Prevalence Rate: Total individuals infected at any one time.   - Prevalence Rate=Total number of cases in populationTotal population\text{Prevalence Rate} = \frac{\text{Total number of cases in population}}{\text{Total population}}
  • Morbidity Rate: An incidence rate measuring new cases per unit of population over a specific time.   - Morbidity Rate=Number of new cases during a specific periodNumber of individuals in population\text{Morbidity Rate} = \frac{\text{Number of new cases during a specific period}}{\text{Number of individuals in population}}
  • Mortality Rate: The number of deaths per total number of disease cases.   - Mortality Rate=Number of deaths due to given diseaseTotal number of cases of the disease\text{Mortality Rate} = \frac{\text{Number of deaths due to given disease}}{\text{Total number of cases of the disease}}

Infectious Disease Dynamics and Trends

  • Common source epidemic: Originates from a single contaminated source, such as food.
  • Propagated epidemic: Spreads from one infected individual into a susceptible group.
  • Emerging and Reemerging Diseases: Driven by world population growth, urbanization, inadequate infrastructure, increased travel, climate change, habitat disruption, and microbial evolution (resistance).
  • Nosocomial Infections: Healthcare-acquired infections affecting 5 to 10%5\text{ to }10\% of hospital patients.   - Prolongs stays by 4 to 14 days4\text{ to }14\text{ days}.   - Adds $28 to $33 billion\$28\text{ to }\$33\text{ billion} in annual costs.   - Results in approximately 99,00099,000 deaths per year.

Vaccines and Immunization

  • Whole-Cell Vaccines: Consist of inactivated (killed) or attenuated (live but avirulent) microbes; considered the gold standard despite risks for the immunosuppressed.
  • Acellular or Subunit Vaccines: Use purified microbial molecules to avoid whole-cell risks, including capsular polysaccharides, recombinant surface antigens, or toxoids (inactivated exotoxins).
  • Recombinant-Vector Vaccines: Insert pathogen genes into nonvirulent vectors to elicit immunity.
  • DNA Vaccines: Introduce pathogen DNA fragments directly into the host for expression and immune response.
  • Vaccinomics: The application of genomics and bioinformatics to vaccine development.

Bioterrorism

  • Definition: The intentional use of biological agents (viruses, bacteria, fungi, or toxins) to cause death or disease.
  • Biological Select Agents and Toxins (BSATs): Examples include Bacillus anthracis, Yersinia pestis, Francisella tularensis, Variola major virus, and Ebola virus.
  • Historical Incidents:   - 1984 (The Dalles, OR): Salmonella enterica serovar Typhimurium in salad bars.   - 1996 (Texas): Intentional release of Shigella dysenteriae in a hospital break room.   - 2001 (Eastern U.S.): Weaponized Bacillus anthracis spores delivered via the U.S. postal system, resulting in 55 deaths.