Uploaded by Akash Samuel

5 Epi Surveillance

Surveillance &
Prince Naeem
BSN-RN, M. Phil (EPI-PH)
Control of Communicable Diseases: Tools
• Isolation
• Treatment
• Disinfection & Barriers
• Quarantine & Surveillance
• Vaccination
• Prophylaxis
Could you drive without looking at the traffic?
Can you make public health decisions in the absence of data?
• French word means watch over.
• Close observation of a person or group, especially one under suspicion.
“The continued watchfulness over the distribution & trends of incidence through
the systematic collection, consolidation, & evaluation of morbidity/mortality
reports & other relevant data, together with dissemination to those who need
to know.” (LANGMUIR, 1963)
”A systematic ongoing collection, collation, analysis of data for public health
purposes & timely dissemination of public health information for assessment
& public health response as necessary.” (World Health Assembly 2005)
Definitions of Surveillance
“Surveillance serves as the brain & nervous system for programs to prevent &
control disease.” (D.A. HENDERSON, 1976)
“Ongoing systematic collection analysis, interpretation of health data, essential to
planning, implementation, & evaluation of public health practice, closely
integrated with timely dissemination of these data to those who need to know. ”
“Continuous analysis, interpretation & feedback of systematically collected data,
generally using methods distinguished by their practicality, uniformity & rapidity,
rather than by accuracy & completeness”. (WJ Eylenbosch & ND Noah: Surveillance
in Health & Disease. Oxford University Press 1988)
Definitions of Surveillance
Key Elements
1. Collection of health data expressly for use in health planning, disease control/
prevention, &/or health promotion
2. Ongoing collection of data
3. Timely analysis
4. Easily understood
5. Dissemination of results
6. Action based on results
7. Periodic evaluation of the system
Historical Perspective
First use for Public Health Action
William Farr (1807 – 1883)
• Superintendent, statistical department, General Register Office, UK
• Collected, analyzed, interpreted vital statistics
• Plotted rise & fall of epidemics of infectious diseases, identifying associations
• Disseminated information weekly/quarterly/annually/medical journals public press
Recognition by World Health Organization
21st World Health Assembly (1968) "Information for action"
• Systematic collection of pertinent data
• Orderly consolidation & evaluation of these data
• Prompt dissemination of the results to those who need to know
Surveillance System/ Loop
Health care system
Surveillance centre
Planning, Evaluation,
Policy formulation
Feedback, recommendations
Event & Population Under Surveillance
– Acute flaccid paralysis
– Influenza-like illness
– Diarrhoea
•Public health issue
– Antimicrobial resistance
– Vector population
– Water quality
•Population & Time
• Everyone in the country or region
• Patients in hospitals
• Employees in a factory
• All children in the winter months
Aims of Surveillance
Process of doing something: examples
• Manage contacts of a case
• Detect outbreaks
• Early warning
• Design/change vaccination policy
• Design policy re antimicrobial resistance
• Evaluate interventions to improve them
• Certify elimination / eradication
Aims of Surveillance
Public Health Aims
 Assess Public Health Status (Monitor Trends, Detect Outbreaks)
- Prevent And Control Disease
 Define Public Health Priorities
- Plan Considering Impact Of Hazard, Exposure, Disease
 Evaluate Public Health Programmes
- Make Decisions Regarding Interventions
 Stimulate Or Inform Research
- Generate Hypotheses, Inform Methodologie
Principles of Surveillance
• A key principle is to include only conditions for which surveillance can
effectively lead to prevention. Another important principle is that
surveillance systems should reflect the overall disease burden of the
community. Other criteria for selecting diseases include:
• The surveillance plan should include a detailed M & E plan
• Incidence & Prevalence
• Indices Of Severity (Case-fatality Ratio)
• Mortality Rate & Premature Mortality
• An Index Of Lost Productivity (Bed-disability Days)
• Medical Costs
• Preventability
• Epidemic Potential
• Information Gaps On New Diseases
• Public Concern & News-worthiness
Requirements for Surveillance
 Diagnostic Algorithm
 Costs
 Availability Of Data
 Staff Members
 Sampling Frame
 Access/Network
 Competent Laboratory
Surveillance Vs. Screening & Research
 Data collection to measure magnitude, changes, & trends in populations
 The objective is intervention in defined populations
 Testing to identify individuals with infection or disease
 Measurement of prevalence in screened populations
 Pursues new knowledge from which better control measures will result
Systematic investigation, testing & evaluation, designed to develop or
contribute to knowledge.
Steps in Setting Up Surveillance System
1. Understand the problem
2. Identify opportunities for prevention & control
- Interventions/Selection of Population
3. Set objectives
4. Specify requirements to meet objectives
5. Design
- Case definitions & indicators/Data needed/Data sources/Data transfer
6. Translate information into action
- Analyse/Interpret/Disseminate
7. Evaluate surveillance system
Understand The Problem
Source Of
Identify Opportunities For Prevention & Control
6. Prevent transmission e.g.
universal precautions
1. Vaccination
4. Isolation/Treatment
Source Of
2. Prophylaxis
5. Ecological Management
3. Treatment
Surveillance Systems
Selecting the Population
Defining the selection criteria
Human populations
Zoonotic populations
Gaining access to target populations
NGOs/support groups
Obtaining & maintaining compliance
Set Objectives
Objectives should be SMART:
• Specific
• Measurable
• Acceptable and Action oriented
• Realistic
• Time related
• To estimate the prevalence of hepatitis C
Specific, Measurable, Action-oriented & Timed
• To assess the prevalence of hepatitis C in Lahore in order to allow planning of
specific health care needs for the coming 20 years
Surveillance Systems
Selecting The Appropriate Strategy & The Reservoir
 Need for cultural sensitivity
 Understanding the implications & limitations of different strategies
 Selecting the appropriate surveillance strategy
 For surveillance, want a representative sample
 For finding the reservoir, or finding infected individuals
Defining A Case (Case Definition)
 Establishing a functional case criteria
 Quickly & easily defined
 Selecting the right test or definition
 Easy, specific
 Clinical versus epidemiological diagnostic criteria
 Function over precision
 Disease versus infection
 AIDS & HIV infection
Case Definition
 NO
A case is an event
A case is not a person
An event is something that happens
Events do not exist if you lack info:
A person,
In a given place,
At a given time
A case definition is a set of criteria
that triggers reporting
On the person
On the place
On the onset date
A case definition is not a diagnosis
made to decide treatment
Surveillance Methods
Key Data Items Collected
– Numerators
– Number of cases of disease
– Antibody positive samples
– Number of resistant strains
– Descriptors
– Characteristics of patients, strains etc
– Denominators
– Total population at risk (or sub-sample) in a given time frame
– Total number of strains examined
Surveillance Data Sources
Common sources
– Notifications of infectious Dx. & biological changes in agent/vectors/reservoirs
– Microbiology laboratory reports & vaccine utilization
– Hospital episode statistics and records
– Primary care spotter practices
– Blood banks & screening programmes (antenatal, blood donors)
– Prescriptions/over the counter drug sales
– Mortality and morbidity reports
– Outbreak reports
– Sickness absence records
For example,
Surveillance Systems
Other Considerations
 Timely data processing
 Results and action
 Interpretation
 Facilitating appropriate action based on surveillance results
Evaluation & Revisions
 Importance of ongoing evaluation
 Revising the surveillance program
 When & Why
Surveillance Systems
Surveillance Study Designs
 Cohort studies
 Cross-sectional studies/surveys
 Serial cross-sectional studies
 Mortality surveillance
 Sentinel surveillance
 Syndromic (early outbreak detection)
Passive Surveillance
• This form of data collection, in which health-care providers send reports to a
health department on the basis of a known set of rules & regulations, is called
Passive surveillance (provider-initiated).
• Passive surveillance often gathers disease data from all potential reporting
health care workers. Health authorities do not stimulate reporting by reminding
health care workers to report disease nor providing feedback to individual health
• Most common type of surveillance in humanitarian emergencies. Most
surveillance for communicable diseases is passive.
 Passive = reporting
 Hospitals, Laboratories, Clinics, Physicians
Active Surveillance
• Active surveillance (health department- initiated) is usually limited to
specific diseases over a limited period of time, such as after a community
exposure or during an outbreak.
• Active surveillance requires significantly more time & resources & is therefore
less commonly used in emergencies.
• Community health workers may be asked to do active case finding in the
community in order to detect those patients who may not come to health
facilities for treatment.
 Active = searching
Sentinel Surveillance
Monitoring of rate of occurrence of specific conditions to assess the stability or
change in health levels of a population. It is the study of disease rates in a
specific cohort such as in a geographic area/population subgroup to estimate
trends in larger population. (CDC)
A sentinel surveillance system is used when high-quality data are needed about a
particular disease that cannot be obtained through a passive system. Selected
reporting units, with a high probability of seeing cases of disease in question,
good lab facilities & experienced well-qualified staff, identify & notify on certain
diseases. A sentinel system deliberately involves only a limited network of
carefully selected reporting sites. (WHO)
Sentinel Groups
Commercial sex workers
Returning overseas workers
Intravenous drug users
Males at STD clinics
Other groups
Analysis Of Surveillance Data
Descriptive use
–Measure of disease frequency
–Incidence (no. Cases/population at risk over given time period)
e.g. 5 cases per 1000 person years; 0.3 cases per 1000 persons
–Prevalence (no. Cases/population at risk at a set time)
e.g. 15% patients sampled antibody +ve; 3% strains erythromycin resistant
–Data described according to time-person-place
Analytical use
–Comparison between groups to gain a measure of increased risk
e.g. Case fatality in males vs females
e.g. Change in rate of infection over time
Characteristics/Requirements & Evaluation of A Surveillance System
 Sensitivity
 Timeliness
 Representativeness
 Predictive value positive
 Acceptability
 Flexibility
 Simplicity
 Cost/benefit
 Dissemination of results
 Appropriate action taken
 Do reported cases differ from unreported cases?
 Is information disseminated rapidly enough to permit timely action
based on the surveillance system?
Predictive Value Positive
 What proportion of those identified actually have the disease or
 What proportion of “cases” are identified?
 Does the system give an accurate picture of trends and magnitudes?
 Does the system stimulate the cooperation of respondents?
 Does the process discourage participation?
 Can changes be easily made in the system to reflect changes in trends,
magnitude, and other relevant factors?
 Can the system be simplified & still obtain the necessary information?
 Is the system worth the cost?
 Can costs be reduced without sacrificing the essential quality of the
system (e.g., each 12 vs each 6 months)?
Dissemination Of Results
 To decision-makers
 To data collectors
 To the general public
Appropriate Action Taken
 Are appropriate actions taken in response to the surveillance data?
 Does surveillance lead to effective intervention?
Uses of Surveillance
• Recognize isolated or clustered cases/early epidemic detection & assess how big
a problem is. i.e.
 Human disease
 Zoonotic diseases
 Food safety
 Drug-resistant organisms (e.g., MDR-TB)
• Assess the Community health impact of events & assess trends/pattern of
disease/health problems.
 Prevalence/incidence of disease and/or risk factors
 Emerging diseases
 Geographic distribution
 Risk group distribution
• Good surveillance is vital for successful control of communicable diseases.
• Measure the causal factors of disease & identify high risk groups.
• Monitor effectiveness, evaluate the impact of prevention & control
measures, intervention strategies & health policy changes
• Plan, provide care & various interventions
• Evaluate various hypotheses about disease occurrence
• Help to identify epidemic outbreaks in order to investigate & control them
• The facility-based health information system should be augmented with a
community based surveillance that uses volunteers & Community health
workers/health information teams to gather essential data through home
visits & other means.
In addition to estimating the magnitude of an epidemic & monitoring its
trends, data can also be used to:
• Strengthen commitment,
• Mobilize communities,
• Advocate for sufficient resources.
Health Indicators
• These are quantifiable characteristics of a population used by researchers
as supporting evidence for describing the health of a population. Typically,
researchers will use a survey methodology to gather information about
certain people, use statistics in an attempt to generalize the information
collected to the entire population, then use the statistical analysis to make
a statement about the health of the population.
• Health indicators are often used by governments to guide health care
Some of the basic health indicators are:
– Crude Birth Rate,
– Crude Death Rate,
– Infant Mortality Rate,
– Morbidity Rate,
– Perinatal Mortality Rate,
– Neonatal Mortality Rate,
– Maternal Mortality Rate,
– Incidence Rate,
– Prevalence Rate,
– Life Expectancy,
– General Fertility Rate.