SURVEILLANCE AND EPIDEMIC OUTBREAK INVESTIGATION Flashcards
Common-vehicle exposure
From a source common to all
Single exposure
Exposed only once
Multiple exposures
Exposed several times
Periodic contamination
Intermittent contamination
Continuous contamination
Persistent contamination
Clinical disease
Characterized by signs and symptoms
Non-clinical disease:
Preclinical, Subclinical, Persistent (Chronic), Latent
Preclinical
symptoms not yet apparent but the disease is biologically present and destined to progress to clinical
Subclinical
symptoms not yet apparent but seropositive
Persistent (Chronic)
manifestation of symptoms for years
Latent
no active multiplication of the agent
Carrier
Harbors organism, can be asymptomatic and seronegative
Incubation period
Interval from receipt of infection to the time of onset of clinical illness
Factors that affect incubation period
- Time of replication
- Site of replication
- Dose of infectious agent
Quarantine (quarante giorni)
Detention period of animal or human
Critical variables in disease investigation:
- When did the exposure take place?
- When did the disease begin?
- What was the incubation period for the disease?
A person who acquires the disease from exposure e.g from contaminated food
Primary Case
Secondary case
• A person who acquires the disease through exposure to primary case
What are the questions to be asked for diseases that occur at more than an endemic level?
• WHO was attacked by the disease?
• WHEN did the disease occur?
• WHERE did the cases arise?
Factors such as sex, age, race, and other host characteristics
WHO?
question to be asked for certain diseases that occur with a certain periodicity
WHEN?
WHERE
question for diseases that are NOT randomly distributed in time or place
The occurrence of disease at an unusual or unexpected, elevated
Epidemics (disease outbreaks)
Entire process of collecting, analyzing, interpreting, and reporting data on the incidence of death, diseases, and injuries and the prevalence of certain conditions, for promoting and safeguarding public health
Surveillance
United States Federal agency responsible for surveillance
HQ: Atlanta, Georgia
Centers for Disease Control and Prevention (CDC)
Development of surveillance system requires (9):
• Clear objectives
• Standardized reporting procedures
• Case definition based on clinical findings
• Determination of intensity of surveillance (Active vs. passive)
• Determination of duration of surveillance (ongoing vs. time-limited)
• Types of analysis (e.g.incidence, prevalence, case fatality ratio, etc.)
• Plans for information dissemination (internet, publication, broadcast)
• Pilot test performed and evaluated first before full system attempt
• Continuous evaluation when full system is operational
METHODS AND FUNCTIONS OF DISEASE SURVEILLANCE
Passive: Physicians (On going)
Active: Surveillance body (As needed)
ESTABLISHMENT OF BASELINE DATA
Through regular reporting and surveillance system
Continued surveillance
Detect deviations from the usual pattern of data and prompts epidemiologists to explore
Secular (Long-term) Trends
• Change in reporting = UNDERESTIMATE incidence
• Change in surveillance = OVERESTIMATE prevalence
Seasonal Variation
• Exhibited by many infectious diseases
• Period of highest incidence depends on route of spread
• Should be incorporated into calculations by epidemiologists
Calendar year
• From Jan.01 to Dec.31
Epidemiologic year
From month of lowest incidence in 1 year to the same month in the next year
Epidemic threshold (WHO)
• Critical number or density of susceptible hosts required for an
epidemic to occur
• Used to confirm the emergence of an epidemic so as to set-up appropriate control measures
Syndromic Surveillance
• Technique to rapidly detect epidemics and possible bioterrorism
• Goal: characterize “syndromes consistent with bioterrorism agents
•To prime the system-to report any such syndromes quickly
•Provides early warning of a bioterrorism problem
Purpose of evaluation
• To track progress of major interventions
• To determine if intended changes were achieved
• To gauge the impact of new vaccines,health policies,etc.
Failure of a vaccine:
• A lack of change in disease rates
• An increase in disease rates after an initial decrease
• An increase in disease rates in a recently vaccinated group
Importance of post marketing surveillance
• Investigators are able to detect any failure in the system
• Measles immunization (2006 recommendations)
• First dose:12-15 months old
• Second dose: 4-6 years old
• Third dose: about the age of 18
Current and past data on the patterns of disease can
help governmental and voluntary agencies establish priorities for disease control efforts
Epidemics (etymology: Greek “upon the population”)
• Can sometimes refer to just one case of a disease
Endemic (etymology: Greek “within the population”)
• Disease occurs regularly at a more or less constant level
Epizootic (etymology:Greek “upon the animals”)
• A disease outbreak in animal population
Enzootic (etymology: Greek “within the animals”)
Disease deeply entrenched in an animal population but not changing much
Attack rate
Proportion of exposed persons that become ill
PROCEDURES / STEPS FOR INVESTIGATING AN EPIDEMIC
STEP 1. ESTABLISH DIAGNOSIS
STEP 2. ESTABLISH EPIDEMIOLOGIC CASE DEFINITION
STEP 3. IS AN EPIDEMIC OCCURRING?
STEP 4. CHARACTERIZE EPIDEMIC BY TIME, PLACE, AND PERSON
STEP 5. DEVELOP HYPOTHESIS REGARDING SOURCE, PATTERNS OF SPREAD, AND MODE OF TRANSMISSION
STEP 6.TEST HYPOTHESIS
STEP 7. INITIATE CONTROL MEASURES
STEP 8. INITIATE SPECIFIC FOLLOW-UP SURVEILLANCE TO EVALUATE CONTROL MEASURES
