16.2 Tracking Infectious Diseases

Epidemiological approaches help us understand how diseases spread and affect populations. From John Snow's cholera investigation to modern study designs, these methods allow researchers to identify risk factors, track outbreaks, and develop prevention strategies.

Observational studies like cohorts and case-controls provide valuable insights, while experimental designs like randomized controlled trials offer the strongest evidence for causation. Each approach has strengths and limitations, shaping our understanding of disease patterns and informing public health interventions.

Epidemiological Approaches and Study Designs

Early epidemiological investigation approaches

Top images from around the web for Early epidemiological investigation approaches

• 

  Epidemiology - wikidoc View original

  Is this image relevant?

• 

  ZUMAYAS EN FORMALINA: El mapa del cólera de John Snow, padre de la epidemiología View original

  Is this image relevant?

• 

  Tracking Infectious Diseases · Microbiology View original

  Is this image relevant?

• 

  Epidemiology - wikidoc View original

  Is this image relevant?

• 

  ZUMAYAS EN FORMALINA: El mapa del cólera de John Snow, padre de la epidemiología View original

  Is this image relevant?

1 of 3

Top images from around the web for Early epidemiological investigation approaches

• 

  Epidemiology - wikidoc View original

  Is this image relevant?

• 

  ZUMAYAS EN FORMALINA: El mapa del cólera de John Snow, padre de la epidemiología View original

  Is this image relevant?

• 

  Tracking Infectious Diseases · Microbiology View original

  Is this image relevant?

• 

  Epidemiology - wikidoc View original

  Is this image relevant?

• 

  ZUMAYAS EN FORMALINA: El mapa del cólera de John Snow, padre de la epidemiología View original

  Is this image relevant?

1 of 3

• John Snow's investigation of the 1854 London cholera outbreak
  • Mapped locations of cholera cases and water sources in the affected area
  • Identified the Broad Street pump as the likely source of contaminated water causing the outbreak
  • Removed the pump handle, which led to a rapid decline in new cholera cases (supporting his hypothesis)
• Robert Koch's postulates for establishing causation between a microbe and a disease
  • The microbe must be present in every case of the disease (consistent association)
  • The microbe must be isolated from the diseased host and grown in pure culture (outside the host)
  • The cultured microbe should cause the same disease when introduced into a healthy organism (demonstrating causation)
  • The microbe must be re-isolated from the inoculated, diseased experimental host and identified as identical to the original specific causative agent (confirming the microbe as the cause)

Observational vs experimental study designs

• Observational studies
  • Cohort studies
    • Follow a group of individuals over time to determine disease incidence and risk factors
    • Can be prospective (follow participants forward in time) or retrospective (look back in time using existing data)
    • Example: Framingham Heart Study (prospective cohort study of cardiovascular disease risk factors)
  • Case-control studies
    • Compare individuals with a disease (cases) to those without the disease (controls)
    • Look for differences in past exposures or risk factors between the two groups
    • Example: Study comparing past smoking habits of lung cancer patients (cases) and healthy individuals (controls)
  • Cross-sectional studies
    • Assess the prevalence of a disease and potential risk factors at a single point in time
    • Cannot establish causation, only association between variables
    • Example: Survey of asthma prevalence and air pollution levels in different neighborhoods
• Experimental studies
  • Randomized controlled trials (RCTs)
    • Participants are randomly assigned to receive an intervention (treatment) or a placebo (control)
    • Considered the gold standard for determining causation by minimizing bias
    • Ethical concerns may limit the use of RCTs in some cases (exposing participants to potential harm)
    • Example: RCT testing the effectiveness of a new vaccine compared to a placebo

Strengths and limitations of epidemiological studies

• Cohort studies
  • Strengths
    • Can establish temporal relationship between exposure and disease (exposure precedes outcome)
    • Can calculate incidence rates and relative risks (quantifying the strength of associations)
  • Limitations
    • Expensive and time-consuming (large sample size and long follow-up period)
    • Loss to follow-up can bias results (participants who drop out may differ from those who remain)
• Case-control studies
  • Strengths
    • Efficient for studying rare diseases or diseases with long latency periods (requiring fewer participants)
    • Less expensive and time-consuming than cohort studies (retrospective design)
  • Limitations
    • Prone to selection and recall bias (cases and controls may differ in their likelihood of being selected or accurately recalling past exposures)
    • Cannot directly calculate incidence rates or relative risks (only odds ratios)
• Cross-sectional studies
  • Strengths
    • Quick and inexpensive (data collected at a single time point)
    • Useful for generating hypotheses and assessing prevalence (snapshot of a population)
  • Limitations
    • Cannot establish temporal relationship between exposure and disease (exposure and outcome measured simultaneously)
    • Prone to biases related to the single time point assessment (may not capture changes over time)
• Randomized controlled trials
  • Strengths
    • Minimize bias through randomization and blinding (ensuring comparable groups and reducing placebo effect)
    • Provide the strongest evidence for causation (by manipulating the exposure variable)
  • Limitations
    • Expensive and time-consuming (requiring large sample sizes and rigorous protocols)
    • May not be ethically feasible for some exposures or diseases (withholding potentially beneficial treatments)
    • Results may not always be generalizable to the broader population (due to strict inclusion criteria)

Disease Monitoring and Control Strategies

• Surveillance systems
  • Continuous, systematic collection, analysis, and interpretation of health-related data
  • Essential for early detection of disease outbreaks and monitoring trends
• Contact tracing
  • Identifying and monitoring individuals who have been in close contact with infected persons
  • Crucial for containing the spread of infectious diseases
• Outbreak investigation
  • Systematic approach to identify the source, mode of transmission, and extent of an infectious disease outbreak
  • Involves epidemiological, laboratory, and environmental components
• Disease modeling
  • Mathematical and statistical techniques to predict the spread and impact of infectious diseases
  • Helps inform public health interventions and resource allocation
• Zoonotic transmission
  • Transfer of pathogens from animals to humans, a significant source of emerging infectious diseases
  • Requires a One Health approach, considering human, animal, and environmental health