Establish a Surveillance System

Detect emerging pathogen, reappearance of an old one, or outbreaks. • Monitor behavior of existing pathogens • Monitor trends in epidemiology: risk factors, age groups, seasonality, etc. • Measure disease burden: absolute (incidence) or relative to other diseases • Evaluate impact of an intervention

Establish

a Surveillance System

Hien Do Epidemiologist, WHO Viet Nam

First question: Why do you want to

conduct surveillance?

• Detect emerging pathogen, reappearance of an old one, or outbreaks

• Monitor behavior of existing pathogens

• Monitor trends in epidemiology: risk factors, age groups, seasonality, etc

• Measure disease burden: absolute (incidence) or relative to other

diseases

• Evaluate impact of an intervention

• It’s helpful to actually write down the objectives

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The answers will determine:

• Will the system be active or passive?

• Will it be a sentinel indicator-based system or an event

detection system

• What diseases will you measure?

 Will it be more than one? based on syndromic

 Surveillance and/or laboratory testing?

• Will this be a new system or will you add on to existing system?

• What population will you monitor?

Decisions to Make

• What data will you collect?

 Decide first, what the major public health questions are

 With a limited sentinel system, can also get risk factor data

such as age, medical conditions, vaccination status, etc

• Who will collect, analyze and report data?

• Who will interpret data and take action?

• How will report be shared and to whom?

• How will system be monitored?

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SETTING UP THE SYSTEM

What are the necessary bits?

Steps to establishing a new system

Data sources

• Identify what data to collect

 Decide how it will be used, what decisions will be based on

the data

 Limit the amount of data to what is actually going to be useful

• Collect data systematically

 Data collection forms

 Case definitions

• Train reporters

Case definition

• Standardization helps compare apples to apples

• Can have different levels of certainty:

 Confirmed, probable, suspect

 Surveillance case definition may differ from clinical diagnostic definitions:

e.g ILI

• Components: diagnostic criteria (lab and clinical); who, where, when

 Is laboratory confirmation required?

 Who: is there an age group of interest? E.g the pediatric influenza mortality

surveillance system If all age groups, how do you aggregate?

 Where: may be especially important for disease burden estimates when a

specific catchment area is under surveillance

 When: some systems may run seasonally, e.g influenza

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Case definition example

• Influenza-like Illness:

An acute respiratory infection with:

 measured fever of ≥ 38 C °;

 and cough;

 with onset within the last 10 days

• Severe acute respiratory infections (SARI)

An acute respiratory infection with:

 history of fever or measured fever of ≥ 38 C °;

 and cough;

 with onset within the last 10 days;

 and requires hospitalization

Case reporting form

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Site Selection Criteria

• Representativeness: what population needs monitoring?

(consider HIV vs Influenza)

 General hospitals may be better than referral centers for some diseases but not others

 Consider variations in climate, ethnicity, risk factors

• Logistics:

 Need to be able to transmit data and clinical specimens

• Patient volume:

 Site should get sufficient number of cases to be meaningful

• Ability to determine denominator:

 Can you estimate the proportion of total cases that are actually reported/tested?

 Can you estimate the size of the catchment population?

How many sites, how many

specimens?

• Number of sites depends somewhat on variety of disease ecology

 Are there differences in climate?

 Is there much diversity in the population?

 Is there a region or population of special interest?

• How many can you afford?

• What portion of total numbers reported are likely to be truly the

disease of interest?

• Number of specimens/cases is not related to population size but

rather prevalence of the disease

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Influenza surveillance

Italy

Rwanda

Albania

Reporting

• Lab based or clinic/hospital

• Mechanism to report: electronic, web, telephone, mail

 Technology is not the answer Get the system working first!

• Immediate reporting of priority diseases:

• Lowest level that reports

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• Laboratory reports and data summaries back to reporting facility

• IHR secure channels

• Meetings and conferences

Monitoring and Evaluation

• Basic indicators should monitor timeliness,

completeness, and validity of data

 However indicators don’t tell the whole story

• Watch for aberrations in the data

 Don’t assume you know the reason

• Keep system small enough that monitoring can assure

the quality of the data

• Periodic audits important to really dig deep

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• Consistency in reporting is critical since the goal is to observe trends

 All must report the same thing

 All must report regularly

• Don’t get ambitious – a little data goes a long way towards

understanding a problem

 Aim for representativeness rather than volume

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