Epidemiology updated

Centers for Disease Control and Prevention (CDC)

  • The CDC is the agency responsible for conducting epidemiological research and protecting public health.

  • An agency of the Department of Health and Human Services.

  • Responsibilities include:

    • Detecting and responding to new and emerging health threats.

    • Studying health issues that cause death or disability in Americans.

    • Taking action to prevent disease using the best science and technology available.

    • Promoting healthy and safe practices in communities and environments.

    • Developing leaders and training the public health workforce, including disease detectives.

    • “Taking the health pulse of our nation” by knowing the frequency and distribution of diseases.

National Notifiable Disease Surveillance System

Morbidity and Mortality Weekly Report (MMWR)

  • The MMWR is a weekly publication of the CDC available on its website.

  • Contains important statistics of all notifiable diseases (diseases of significant public health importance).

  • The occurrence of these notifiable diseases must be reported.

  • Reporting process:

    • Doctors' offices, hospitals, etc. report to local or hospital epidemiologists.

    • Local reports are then forwarded to state epidemiologists and ultimately to the CDC.

  • Definitions:

    • Mortality: deaths; Morbidity: illness.

    • Mortality rate: percentage of people who died from a particular disease compared to all who contracted it.

Epidemiologic Terminology

Morbidity Rate

  • The morbidity rate is the number of new cases of a particular disease that occurred per a defined population over a specified time period (often per 1,000, 10,000, or 100,000).

Incidence and Prevalence

  • Incidence Rate: Number or proportion of new cases in a specific timeframe.

  • Prevalence: Total cases of a disease; typically higher than incidence in chronic diseases.

    • Period Prevalence: Number of cases existing in a population during a specific time period.

    • Point Prevalence: Number of cases existing at a particular moment in time.

Relevance of Epidemiology to Medical Professionals

  • Disease Awareness: Tracking notifiable diseases provides healthcare professionals with crucial information about potential public health risks.

  • Determining Etiology: Identifying the cause of diseases.

  • Tracking Disease Spread: Monitoring how diseases are disseminated within populations.

  • Preventing Disease: Epidemiologists study the patterns of disease occurrence to implement control measures to prevent future outbreaks.

Epidemiologic Terminology

Definitions of Disease Types

  • Communicable Disease: Infectious diseases that can be transmitted from one person to another.

  • Contagious Disease: Communicable diseases that are easily transmitted.

  • Iatogenic Disease: Diseases resulting directly from medical procedures.

  • Zoonotic Diseases: Diseases humans acquire from animal sources.

  • Etiology: Cause of disease.

  • Etiologic Agent: The organism that causes a disease (e.g., Lyme disease caused by Borrelia burgdorferi).

Additional Epidemiologic Terminology

  • Incidence: Number of new cases in a specific timeframe.

  • Expected Prevalence: Number of cases usually present in a population at that time of year.

  • Propagation: Spreading of disease.

  • Herd Immunity: Immunity in most of a population.

Patterns of Incidence of Disease

Types of Diseases

  • Endemic Disease: Constantly present in a population (e.g., Malaria).

  • Sporadic Disease: Occurs occasionally and is not associated with a specific area (e.g., Tetanus).

  • Outbreak: Sudden unexpected occurrence of disease, usually localized.

  • Epidemic Disease: Sudden increase in frequency above expected levels.

  • Pandemic Disease: Worldwide epidemic (e.g., Influenza, HIV/AIDS).

Epidemiologists Determine

  • Etiological Agent: What causes the disease.

  • Source (Reservoir): Where the disease originates.

  • Transmission Modes: How the disease spreads.

  • Social/Environmental Conditions: Factors contributing to disease spread.

  • Control Measures: Identifying and employing effective preventative strategies.

Disease Specific Characteristics

  • Source: Location from which a pathogen is transmitted.

  • Reservoir: The natural environment where a pathogen is commonly found.

    • Examples: contaminated water, soil, or animal hosts.

  • Carrier: A human source of a pathogen.

  • Period of Infectivity: Time during which a source is infectious.

  • Incubation Period: Time between exposure to infection and symptom onset.

Types of Reservoirs of Infection

  • Living Reservoirs: Humans, pets, animals, insects.

  • Human Carriers: Individuals carrying diseases without symptoms (e.g., AIDS).

    • Types of carriers include:

    • Passive (asymptomatic)

    • Incubatory (exposed but not sick)

    • Convalescent (recovering)

    • Active (symptomatic)

  • Nonliving Reservoirs: Contaminated soil, water, air.

Types of Sources

  • Point Source: Short-term sources of disease (e.g., contaminated food).

  • Continual Common Source: Extended period of disease spread (e.g., contaminated well).

  • Intermittent Common Source: Causes occasional outbreaks due to environmental factors.

Modes of Transmission Terminology

  • Fomite: Object contaminated with pathogens.

  • Vehicle: Contaminated food or water.

  • Vector: Insects or arachnids that transmit infections.

  • Nosocomial Infection: Healthcare-associated infections.

Modes of Transmission

Types of Transmission

  • Contact Transmission: Involves some form of contact (direct or indirect).

  • Droplet Spread: Spread through the air at close quarters.

  • Vehicle Transmission: Contaminated food, water, or air.

  • Vector Transmission: Transmitted by insects or arachnids.

Mechanisms of Transmission

Direct Contact

  • Skin to skin, sexually transmitted, droplet spread, vertical transmission (mother to child).

Indirect Contact

  • Fomites and various vehicles (contaminated food, water, air).

Indirect Contact (Fomites)

  • Inanimate objects that can transmit pathogens (e.g., doorknobs, towels, hospital equipment).

Vehicles: Contaminated Food or Water

Water Pollution

  • Critical for survival; types of pollution include chemical and biological.

  • An example of a waterborne epidemic includes the 1993 cryptosporidiosis outbreak in Milwaukee.

  • Fecal-oral route transmission highlights issues arising from improper sanitation.

Airborne Transmission

  • Droplets spread through the air over distances greater than 1 meter.

  • Certain pathogens are highly contagious and can survive longer in aerosols than others (e.g., Tuberculosis).

Vector Transmission

  • Insects and arachnids serve as vectors for disease (e.g., Lyme disease).

  • Mechanical Transmission: Pathogen carried by vector on feet.

  • Biological Transmission: Pathogen reproduces in the vector.

Chain of Infection

  • Infectious Agent: Must enter a host.

  • Reservoir: Where the pathogen comes from.

  • Mode of Transmission: How the pathogen spreads to a new host.

  • Portal of Entry: How the pathogen enters a susceptible host.

Breaking the Chain of Infection

Strategies

  • Treating infections: Use of antimicrobial agents.

  • Controlling reservoirs: Disinfecting surfaces and equipment.

  • Preventing portals of exit: Implementing hand hygiene and proper disposal methods.

Transmission Control Strategies

  • Based on mode of transmission:

    • Contact Precautions: Use of gowns, gloves, and disinfection.

    • Vehicle Precautions: Ensure safe food and water practices.

    • Airborne Precautions: Isolation and HEPA filters.

    • Vector Control: Reducing populations of disease-carrying vectors.

Standard Precautions

  • Essential measures in healthcare settings (e.g., hand hygiene, use of PPE).

  • Proper placement of patients and equipment disinfection is paramount to reduce disease spread.

Additional Breaking the Chain of Transmission

  • Contact Precautions: Extra measures to prevent the spread of touch-transmitted pathogens.

  • Droplet Precautions: Enhancements for respiratory droplet transmission (e.g., masks).

  • Airborne Precautions: Strict measures for airborne diseases, including N-95 masks and negative pressure rooms.

Strategies to Control Epidemics

  • Employ interventions that break the chain of infection effectively.

  • Vaccinations: Critical in establishing herd immunity and reducing disease incidence.

  • Vector Control: Using insecticides to control populations of disease vectors.

  • Clean Water Access: Ensuring chlorinated water supply to prevent waterborne illnesses.

  • Quarantine: Isolating infected individuals to minimize public spread.

Quarantine as a Control Method

  • Quarantine effectively separates infected individuals from susceptible populations.

  • Social Distancing: Helpful in controlling droplet transmission through physical separation.