Epidemiologic Surveillance

• Surveillance - the entire process of collecting, analyzing, interpreting, and reporting data on the incidence of death, diseases, and injuries and the prevalence of certain conditions.
• Surveillance is generally considered the foundation of disease control efforts.
• Centers for Disease Control and Prevention (CDC) - the federal agency responsible for the surveillance of most types of acute diseases and the investigation of outbreaks.
• World Health Organization (WHO) - a specialized agency of the United Nations concerned with international public health.
• Since its creation in 1948, the WHO has played a leading role in the eradication of smallpox.
• Creating a Surveillance System

  • The development of a surveillance system requires clear objectives regarding the diseases or conditions to be covered
• Information needed for creating a surveillance system:

  • Intensity of the planned surveillance and duration of the surveillance needed
  • Types of analysis needed
  • Pilot needed
• Methods of surveillance

  • Passive Surveillance
  • Active Surveillance
• Passive surveillance - physicians, clinics, laboratories, and hospitals required to report disease are given the appropriate forms and instructions, with the expectation that they will record all cases of reportable disease that come to their attention.
• Active surveillance - requires periodic (usually weekly) telephone calls, electronic contact, or personal visits to the reporting individuals and institutions to obtain the required data.
• Active surveillance is more labor intensive and costly, so it is seldom done routinely.
• Epidemic or disease outbreak - the occurrence of disease at an unusual (or unexpected) frequency.
• Syndromic surveillance - characterizes "syndromes" that would be consistent with agents of particular concern and to prime the system to report any such syndromes quickly,
• Procedures for investigating an epidemic:

  • Establish the Diagnosis
  • Establish Epidemiologic Case Definition
  • "Is an Epidemic Occurring?"
  • Characterize Epidemic by Time, Place, and Person
  • Develop Hypotheses Regarding Source, Patterns of Spread, and Mode of Transmission
  • Test Hypotheses
  • Initiate Control Measures
  • Initiate Specific Follow-up Surveillance to Evaluate Control Measures
• Pattern of Spread - the pattern by which infection can be carried from the source to the individuals infected.
• Common-source outbreaks - may have only one brief point-source exposure
• Mode of transmission:

  • Respiratory
  • Fecal-Oral
  • Vectorborne
  • Skin to skin
  • Through exchange of serum or other body fluids
• Laboratories studies are important in testing epidemiologic hypotheses and may include one or more of the following:

  • Cultures from patients and, if appropriate, from possible vehicles, such as food or water
  • Stool examinations for ova and parasites
  • Serum tests for antibodies
  • Tests for nonmicrobiologic agents, such as toxins or drugs
• Examples of control measures:

  • Sanitation
  • Prophylaxis
  • Diagnosis and treatment
  • Control of disease vectors
• Sanitation - often involves modification of the environment to reduce the spread of disease.
• Prophylaxis - implies putting a barrier to the infection, such as a vaccine, within the susceptible hosts.
• Diagnosis and treatment - are performed for the person who are infected so that they do not spread the disease to others.
• Control of disease vectors - includes mosquitoes (involved in malaria, dengue, and yellow fever) and Ixodes ticks (involved in Lyme disease).
• The goal of surveillance is to detect outbreaks early enough to prevent further transmission of an infectious agent.
• Interstate implications - outbreaks that originated in one state and have spread to other states.
• Intrastate implications - outbreaks confined within one state's borders.
• • Interstate outbreaks - CDC
  • Intrastate outbreaks - the state government
• Case definition is usually based on:

  • Clinical findings
  • Laboratory results
  • Epidemiologic data
• Epidemiologic year - is used by the CDC to illustrate the incidence of diseases which runs from the month of lowest incidence in one year to the same month in the next year.
• Seasonal variation - refers to the occurrence of disease during certain months or seasons, such as influenza occurring more frequently during winter months.
• Secular trends - are long-term changes in disease patterns that may be influenced by factors like improved sanitation, vaccination programs, or lifestyle changes.
• Epidemic threshold - is used to compare the expected percentage of deaths from a certain disease to the reported percentage
• Bioterrorism - the deliberate release of a pathogenic agent by a person or group.
• Examples of diseases considered major threats for bioterrorism:

  • Anthrax
  • Botulism
  • Brucellosis
  • Plague
  • Smallpox
  • Tularemia
  • Viral hemorrhagic fevers
• The failure of a vaccine to produce satisfactory immunity or the failure of people to use the vaccine can be detected by one of the following:

  • lack of change in disease rates
  • increase in disease rates after an initial decrease
  • increase in disease rates in a recently vaccinated group
• When a disease in a population occurs regularly and at a relatively constant level, it is said to be endemic.
• Zootic - a disease outbreak in an animal population
• Enzootic - a disease deeply entrenched in an animal population but not changing much
• Attack rate - the number of new cases of a disease in a population per 1000 people
• Attack rate - the proportion of exposed persons that becomes ill.