OUTBREAK SURVEILLANCE

Timeliness
Representation
Sensitivity
Specificity

Objective of Surveillance(CDC)

Timeliness,

to implement effective control measures;

Representation,

to provide an accurate picture of the temporal trend
of the disease;

Sensitivity,

to allow identification of individual persons with disease
to facilitate treatment, quarantine, or other appropriate control measures;
and

Specificity,

to exclude persons not having the disease.

CDC

-is the main federal agency for disease surveillance and
outbreak investigation.
-acts whem
Requested by a state, or an outbreak may affect multiple states.

Federal government

Handles interstate outbreaks.

State governments

Handle intrastate outbreaks.

HOW TO CREATE A SURVEILLANCE SYSTEM?

1. Objectives of a Surveillance System

2. Case Definition and Standardizations

3. Surveillance Design

4. Data Dissemination

5. Testing and Evaluation

ACTIVE SURVEILLANCE, PASSIVE SURVEILLANCE

Methods of Disease Surveillance

PASSIVE SURVEILLANCE

Routine reporting by doctors, hospitals, labs
Health professionals report notifiable diseases
Involves less effort and cost
May miss unreported or undiagnosed cases

ACTIVE SURVEILLANCE

Health authorities actively seek information
Regular contact (calls, visits, emails) to clinics/labs
More accurate but costly and time-consuming
Used during outbreaks or special programs

1. ESTABLISHMENT OF BASELINE DATA

BASELINE = USUAL DISEASE LEVELS IN A POPULATION
*ESTABLISHED THROUGH CONTINUOUS DATA
COLLECTION OVER TIME
*HELPS IDENTIFY TRENDS AND ABNORMAL
CHANGES
*KEY TO DETECTING POTENTIAL OUTBREAKS

2. EVALUATION OF TIME TRENDS

SECULAR( LONG TERM) TRENDS
*TrENDS OBSERVED OVER YEARS OR DECADES
*SHOW REAL CHANGES IN DISEASE PATTERNS AND
BEHAVIOR
*MORE SIGNIFICANT THAN SHORT-TERM
OUTBREAKS
*HELP IN POLICY-MAKING AND PUBLIC HEALTH
PLANNING
SEASONAL VARIATION
*Time of year
*How disease spreads
Calendar Year: January to December
Epidemiologic Year: Starts at the lowest point of disease
incidence and ends the next year at the same month

3. IDENTIFICATION AND
   DOCUMENTATION OF OUTBREAKS

Epidemic
Pandemic
Endemic

EPIDEMIC THRESHOLD
-A CALCULATED NUMBER SHOWING THE
EXPECTED MAXIMUM OF DISEASE CASES
OR DEATHS
-IF CURRENT DATA IS HIGHER THAN THIS
THRESHOLD, IT SIGNALS A POSSIBLE
OUTBREAK
VARIES BY DISEASE, SEASON, AND
LOCATION

WHAT IS BIOTERRORISM?
BIOTERRORISM IS THE INTENTIONAL USE OF HARMFUL GERMS (LIKE VIRUSES OR BACTERIA)
TO MAKE PEOPLE, ANIMALS, OR PLANTS SICK OR DIE.
WHY IT’S A CONCERN:
CAN SPREAD QUICKLY AND SILENTLY
HARD TO DETECT AT FIRST
MAY AFFECT LARGE AREAS AND MANY PEOPLE
HOW WE DETECT IT:
WE USE DISEASE SURVEILLANCE TO CATCH UNUSUAL ILLNESS PATTERNS EARLY.
SYNDROMIC SURVEILLANCE:
TRACKS GROUPS OF SYMPTOMS (LIKE FEVER, COUGH) BEFORE DIAGNOSIS. IT GIVES EARLY
WARNING SIGNS OF POSSIBLE ATTACKS.

4. Evaluation of Public Health and Disease Interventions

After vaccines or treatments are introduced,
surveillance must continue
Purpose:
To check if the intervention works
Detect:
Failures in vaccines
Low public uptake
Unexpected side effects

5. Setting of Disease Control
   Priorities

How fast it’s spreading?
How severe or deadly it is?
Its potential to become an epidemic?

BASELINE

USUAL DISEASE LEVELS IN A POPULATION
*ESTABLISHED THROUGH CONTINUOUS DATA
COLLECTION OVER TIME
*HELPS IDENTIFY TRENDS AND ABNORMAL
CHANGES
*KEY TO DETECTING POTENTIAL OUTBREAKS

SECULAR( LONG TERM) TRENDS

*TrENDS OBSERVED OVER YEARS OR DECADES
*SHOW REAL CHANGES IN DISEASE PATTERNS AND
BEHAVIOR
*MORE SIGNIFICANT THAN SHORT-TERM
OUTBREAKS
*HELP IN POLICY-MAKING AND PUBLIC HEALTH
PLANNING

SEASONAL VARIATION

*Time of year
*How disease spreads

Calendar Year

January to December

Epidemiologic Year

Starts at the lowest point of disease
incidence and ends the next year at the same month

Epidemic

-Spreads rapidly within a finite geographical area

Pandemic

-Spreads rapidly across several countries, continents, or the world

Endemic

-Consistently present in the population, with relatively low spread

EPIDEMIC THRESHOLD

-A CALCULATED NUMBER SHOWING THE
EXPECTED MAXIMUM OF DISEASE CASES
OR DEATHS
-IF CURRENT DATA IS HIGHER THAN THIS
THRESHOLD, IT SIGNALS A POSSIBLE
OUTBREAK
VARIES BY DISEASE, SEASON, AND
LOCATION

BIOTERRORISM

IS THE INTENTIONAL USE OF HARMFUL GERMS (LIKE VIRUSES OR BACTERIA)
TO MAKE PEOPLE, ANIMALS, OR PLANTS SICK OR DIE.

WHY BIOTERRORISM IS A CONCERN:

CAN SPREAD QUICKLY AND SILENTLY
HARD TO DETECT AT FIRST
MAY AFFECT LARGE AREAS AND MANY PEOPLE

HOW WE DETECT BIOTERRORISM:

WE USE DISEASE SURVEILLANCE TO CATCH UNUSUAL ILLNESS PATTERNS EARLY.

SYNDROMIC SURVEILLANCE:

TRACKS GROUPS OF SYMPTOMS (LIKE FEVER, COUGH) BEFORE DIAGNOSIS. IT GIVES EARLY WARNING SIGNS OF POSSIBLE ATTACKS.

Epidemic

-Origin: Greek — epi (upon) + demos (people) = "upon the people"
-The unexpected or unusual occurrence of a disease in a population over a specific time.

Endemic

-Origin: Greek — en (within) + demos (people) = "within the people"
-A disease that is consistently present in a particular region or population.

Epizootic

-(epi = upon, zoon = animal)
-Disease outbreak in animals
-E.g., Avian flu outbreak in poultry farms

Enzootic

-(en = within, zoon = animal)
-Constant presence of a disease in animal populations
-E.g., Rabies in wild bats or raccoons

Attack Rate

A measure of risk used during short-term disease outbreaks
to show how many exposed people become ill.

1. Establish the Diagnosis
2. Establish Epidemiologic Case Definition
3. Determine if an Epidemic Is Occurring
4. Characterize Epidemic by Time, Place, and Person
5. Develop Hypotheses Regarding Source, Patterns of Spread, and
   Mode of Transmission
   6.Test Hypothesis
6. Initiate Control measures
7. Initiate Specific Follow-up Surveillance to
   Evaluate Control Measures

B. PROCEDURE FOR INVESTIGATING EPIDEMICS

A. Source of Infection

Identify who or what introduced the disease into the population.
Examples:
Fort Bliss, 1976: An infected food handler contaminated spaghetti, leading to a sudden outbreak.

Milwaukee, 1993: A Cryptosporidium outbreak was caused by contaminated public water over several days.Fort Bliss, 1976

An infected food handler contaminated spaghetti, leading to a sudden outbreak.

Milwaukee, 1993

A Cryptosporidium outbreak was caused by contaminated public water over several days.

B. Pattern of Spread

1. Common Source

2. Propagated Spread

3. Mixed Pattern

1. Common Source

All affected individuals were exposed to the same source.
Point-source: A single exposure event (e.g., one contaminated meal at Fort Bliss).
Continuous-source: Ongoing exposure over time (e.g., Milwaukee water system).

2. Propagated Spread

Person-to-person transmission over time (e.g., influenza, HIV, COVID-19).

3. Mixed Pattern

Begins with a common source, followed by person-to-person spread.
Example: Campers infected by contaminated water later spread the disease to household
members

Point-source:

A single exposure event (e.g., one contaminated meal at Fort Bliss).

Continuous-source:

Ongoing exposure over time (e.g., Milwaukee water system).

C. Mode of Transmission

-Respiratory
-Fecal-Oral
-Bloodborne/Body Fluids
-Vector-Borne
-Fomite Contact

Respiratory

Spread through droplets or aerosols (e.g., measles,
COVID-19)

Fecal-Oral

Ingesting pathogens from contaminated food or water (e.g., cholera, Shigella)

Bloodborne/Body Fluids

Transmission through shared needles or sexual contact (e.g., HIV, hepatitis B)

Vector-Borne

Spread by insects like mosquitoes (e.g., malaria, dengue)

Fomite Contact

Transmission via contaminated surfaces or objects (e.g., bed linens, door handles)