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INTRODUCTION TO SURVEILLANCE

Questions

• What do you think of when you hear the word “surveillance”?

• What do you suppose is the definition of surveillance when applied to infection prevention and control?

Learning Objectives

• Define surveillance and its role in an infection prevention and control program

• Describe types of surveillance and advantages and disadvantages of various surveillance strategies

• Give examples of basic measures of disease frequency and describe applications

Public Health Surveillance Definition

The ongoing, systematic collection, analysis, and interpretation of health-related data essential to the planning, implementation, and evaluation of public health practice, closely integrated with the timely dissemination of these data to those responsible for prevention and control

Surveillance in the Healthcare Setting

Surveillance of healthcare—acquired infections (HAI) is the foundation for organizing, implementing, and maintaining an effective infection prevention and control (IPC) program in the health care facility

“If you don’t measure it, you cannot improve it”

~ Lord Kelvin

Considerations for Surveillance

Frequency Severity Cost Preventability Communicability

Methodologic Issues

GoalsCausal pathwayInformation needs Data sources, methodsCase definitionEvaluation: Balance of attributesInterpretation of data

Interpretation of DataIssues to Consider

Source of dataReliability of diagnosisPotential biases in

detection/diagnosisDefinition of a caseCompleteness of dataReporting biasConsistency in data collectionCompleteness Context

Surveillance in the Healthcare Setting:Objectives

Establish endemic or baseline rate of infections

Compare HAI rates within/between health care facilities

Engage clinical team to adopt best practices Introduce evidence-based and cost-effective

interventions to reduce HAIIdentify and control outbreaksEvaluate success of the ICP interventionsIdentify priority areas to allocate resources

Ultimate aim is to reduce HAI

Components of a Strong Surveillance Program

SystematicOngoingData CollectionAnalysisInterpretationDisseminationAction

Surveillance in the Healthcare Setting

Data must be Collected Validated Analyzed Interpreted Disseminated in a timely manner

Collecting and recording data is useless if no further action is taken Surveillance is synonymous with the premise of

“information for action”

Surveillance in the Healthcare Setting:Methods

When applicable, data set should include:Information on the infected patient or

residentInformation on medical treatment or

procedures at the time of infectionAny underlying medical risk factors of the

patient

Information on both numerator and denominator data should be collected for the calculation of rates of infection

Surveillance in the Healthcare Setting:Methods

Flexible to address challenges Technological changes within the health care facility Short lengths of stay Healthcare worker shortage and turnover Increased frequency of invasive procedures or devices Post-discharge surveillance, as appropriate

Characteristics of a Strong Surveillance Program

Targets Infection prevention Performance improvement Patient safety Public health activities

Engages in mandatory and public reporting

Characteristics of a Strong Surveillance Program

Able to identify risk factors for infection Adverse events Outbreaks Emerging infectious diseases Antibiotic-resistant organisms Bioterrorist events

Implements control or risk-reduction measures

Monitors the effectiveness of intervention

Various Methods of Surveillance Used in Infection Control

Methods Source of Data Comments

Continuing surveillance of all patients (Prospective, active surveillance)

Medical, nursing, laboratory records

Time-consuming and not cost-effective. Infection rates are low in some specialties.

Ward liaison Twice-weekly visits to wards

Discuss all patients with staff and review records

Less comprehensive than continuing surveillance, with similar disadvantages.

Laboratory-based Laboratory records only Depends on samples taken and information on request form.

Laboratory-based ward surveillance/selected continuing surveillance

Reporting of laboratory records and outbreaks by ward staff and continuing surveillance in special units or infections

Early detection of outbreaks and incidence in studies in selected areas of infection.

Adapted from: Glenister HM, Taylor LJ, Bartlett CLR, et al. An evaluation of surveillance methods for detecting infections in hospital inpatients. Journal of Hospital Infection 1993; 23:229-42.

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Various Methods of Surveillance Used in Infection Control

Strategy Pros Cons

Incidence Provides data on infections due to all organisms, on all infection sites, and on all unitsIdentifies clusters

Establishes baseline infection rates

Allows outbreaks to be recognized early

Identifies risk factors

Expensive and labor intensive

Large amounts of data collected with little time for a analysis

No defined prevention objectives

Difficult to develop interventionsNot all infections are preventable

Prevalence Inexpensive

Efficient use of time; can be done periodically

Over-/underestimates infection rates; does not capture data on relevant differences

Limited value in small facilities

Various Methods of Surveillance Used in Infection Control

Strategy Pros Cons

Site-specific Flexible and can be combined with other strategies

Identifies risk factors

No defined prevention strategies or objectives

Denominator may be inadequate

Unit specific Focuses on patients at greater risk

Simplified and reduces personnel

May miss clusters

Denominator may be inadequate

Objective or priority-based

Can be adaptable to facilities with special populations or resources

Focuses on specific issues at the facility

Identifies risk factors

Baseline infection rates are not available

May miss clusters or outbreaks

Adapted from: Perl TM, Chaiwarith R. Surveillance: An overview. Practical Healthcare Epidemiology, 3rd Ed., pp. 111-142, Chicago, IL: University of Chicago Press, 2010.

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Types of Surveillance: Outcome Surveillance

Objective: COUNT number of HAI Informs the magnitude of the problem

Disadvantages: No information on what factors contribute

to the problem No internationally agreed definitions on

surveillance Most commonly used: CDC/NHSN (USA) and ECDC

(Europe) Assumes availability of good diagnostic laboratory

support

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Types of Surveillance: Process Surveillance

Objective: MONITOR adherence to evidence-based or best practices

Essential to prioritize which processes/steps to monitor

Disadvantages: Reliability of data Good compliance does not equate with

effectiveness

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Example of Outcome vs. Process Surveillance

Hand Hygiene

Daily Review

Skin Disinfection

Maximum Barrier

Precautions

Optimal catheter

site selection

OUTCOME SURVEILLANCE

Counting number of CR-

BSIs

PROCESS SURVEILLANCE

Monitoring compliance with CVC care bundle elements

Adapted from Damani, N. Manual of Infection Prevention and Control, Third Edition. New York: Oxford University Press, 2012.

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Recommended Minimum Elements in a Data Set for Surveillance

Patient /resident information– Name or unique identifier, DOB, sex, MRN, ward or unit

in facility, name of consultant, date of admission, onset date, date of discharge or death, site of infection/colonization, organism isolated with antibiotic sensitivities

Medical treatment/procedures– At time of infection– Underlying medical risk factors, clinical outcome,

assessment of whether the incident was preventable

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Linelist: Example

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Considerations

All types of surveillance are expensive and time-consuming

Essential that definitions and objectives of surveillance must be agreed with the clinical team

Identify resources

Personnel involved in surveillance must be trained

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Summary

Assess population and identify those at greatest risk for outcome or process of interest

Select outcome or process for surveillance– Examples of outcomes: HIA, infection or colonization

with a specific organism, sharps injuries– Examples of processes: Central line insertion practices,

influenza vaccination rates, personnel compliance with protocols

Determine observation period

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Summary (continued)

Choose surveillance methodology

Monitor for outcome or process using standardized definitions for all data collected

Collect appropriate denominator data, if rates are to be calculated

Analyze data

Report in a timely manner

ReferencesDamani, N. Manual of Infection Prevention and Control, Third Edition. New York: Oxford University Press, 2012.

DHHS/CDC . Outline for Healthcare-Associated Infections Surveillance, 2006.

Tokars JI, Richards C, Andrus M, et al. The Changing Face of Surveillance for Health Care—Associated Infections. Clinical Infectious Diseases 2004; 39: 1347-52.

Horan TC, Andrus M, Dudeck MA. CDC/NHSN surveillance definition of health care—associated infection and criteria for specific types of infection in the acute care setting. American Journal of Infection Control 2008; 36:309-32.

Haley RW, Culver DH, White JW, et al. The efficacy of infection surveillance and control programs in preventing nosocomial infection in US hospitals. (SENIC study). American Journal of Epidemiology 1985; 121(2):182-205.

Lee TB, Montgomery OG, Marx J, et al. Recommended practices for surveillance: Association for Professionals in Infection Control and Epidemiology (APIC), Inc. American Journal of Infection Control 2007; 35(7):427-40.

HICPAC guidance on public reporting of healthcare-associated infections: Recommendations of the Health care Infection Control Practices Advisory Committee. Infection Control Hospital Epidemiology 2005; 26(6):580-7.

“Good surveillance does not necessarilyensure the making of right decisions,but it reduces the chances of wrong ones.”

-Alex Langmuir, NEJM 1963: 268:182-191

MEASURES OF DISEASE FREQUENCY

“One’s knowledge of science begins when he can measure what he is speaking about and express it in numbers”

Lord Kelvin 1824-1907

Measures in General

Count Ratio Proportions Rate

EPIDEMIOLOGIC MEASURES

Measures of frequency Incidence Prevalence Interrelationship between incidence and

prevalence

COUNT

Simple measure of quantity

Example: The number of catheter-related bloodstream infections (CR-BSIs) in Facility X in 2012.

RATIO

An expression of the relationship between a numerator and a denominator where the two are separate and distinct quantities.

Example: Injurious falls occur in twice as many women aged 65-69 years as in men of the same age group.

Ratio of women to men is 2/1 or 2:1

PROPORTION

A type of ratio in which the numerator is

included in the denominator.

EXAMPLE OF PROPORTION

650 HIV+ patients were seen at Facility X.

130 of these patients had Pneumocystis carinii pneumonia (PCP).

Proportion of HIV+ patients seen at Facility X with PCP is 130/650.

130/650 *100 = 20%

RATE

An expression of the frequency with which an event occurs in a defined population.

A measure of time is an intrinsic part of

the denominator.

EXAMPLE OF RATE

435/1,000 elderly individuals residing in assisted living facilities had colds in January.

(The 435 elderly residents with colds are part of the 1,000 residents in assisted living facilities.)

TYPES OF RATES

Morbidity rates measure the frequency of

illness within a specific population. Incidence Prevalence Attack rate

Mortality rates measure the frequency of

death within a specific population. Crude death rate Cause-specific death rate Case-fatality rate

MEASURES OF DISEASE FREQUENCY

Measures that characterize the occurrence of disease, disability or death in populations.

Incidence Prevalence

MEASURES OF DISEASE FREQUENCY

Incidence (I): Measures new cases of a disease or health event that develop over a period of time.

Prevalence (P): Measures existing cases of a disease at a particular point in time or over a period of time.

INCIDENCE

The number of new cases of disease

that occur in a specified period of time.

There are two kinds of incidence measures:· Cumulative incidence (CI)· Incidence density (ID) or incidence rate (IR)

CUMULATIVE INCIDENCE

The proportion of unaffected individuals who contract disease during a specified time.

CI = # of new cases in a given time Total population at risk

(Estimate of individual risk)

PROBLEMS WITH USING CI

To accurately calculate CI we need to follow the entire population for the specified time interval.

This is rarely possible for two main reasons People move in and out People may die from diseases other than disease

of interest

INCIDENCE RATE

The instantaneous potential for change in disease status per unit of time.

IR = # new case in a given timeTotal person-time of observation

Ranges from 0 to

WHAT DENOMINATOR DATA TO COLLECT?

For device-associated HAI incidence rates: Daily total number of patients AND Total number of ventilator-days, central

line-days, and urinary catheter-days in patient care area(s) under surveillance

Sum daily counts at the end of the surveillance period for use as denominators

Denominator data may be collected by someone other than the ICP as long as that person is trained

INCIDENCE RATE EXAMPLE

Three people out of ten persons observed develop disease during a 30-day period of follow-up.

The cumulative rate = 3 cases in 30 days 10 people

or 1 per 100 per day

(3/10 = 0.3 * 100 = 30/30 days = 1 = incidence for one day per 100 people)

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ATTACK RATE

Another type of incidence rate Expressed as cases per 100 population (or

a percentage) Used to describe the new and recurrent

cases of disease that have been observed in a particular group during a limited time period in special circumstances, such as during an outbreak

Attack rate:Number of new and recurrent cases in a specified time period Population at risk for same time period

X 100

PREVALENCE

Measures existing cases of a health condition

Two types of Prevalence Point prevalence Period prevalence

POINT PREVALENCE

Point Prevalence = C / N

Where C = Number of observed cases at time tAnd N = Population size at time t

Point prevalence measures the frequency of disease at a given point in time.

POINT PREVALENCEEXAMPLE

Suppose there are 150 individuals in a population and, on a certain day, 15 are ill with the flu. What is the estimated prevalence for this population?

P = 15/150 = 10%

PERIOD PREVALENCE

Period Prevalence = [C + I] / N

C = the number of prevalent cases at the beginning of the time period.

I = the number of incident cases that develop during the period.

N = size of the population for this same time period.

EXAMPLE

What is the prevalence of disease X on January 1, 1992?Point Prevalence = C/N = 0/10 = 0%

EXAMPLE

What is the period prevalence of disease X between 1990 and 1995?Period Prevalence = [0 + 5] / 12 = 42%

PREVALENCE

Useful for: Assessing the health status of a population. Planning health services.

Not Useful for: Identifying risk factors

ANOTHER EXAMPLE

Suppose we followed a population of 150 persons for one year, and 25 had a disease of interest at the start of follow-up and another 15 new cases developed during the year.

What is the point prevalence at the start of the period?

What is the period prevalence for the year?

What is the point prevalence at the end of period?

What is the cumulative incidence for the one year period?

ANOTHER EXAMPLE

Suppose we followed a population of 150 persons for one year, and 25 had a disease of interest at the start of follow-up and another 15 new cases developed during the year.

What is the point prevalence at the start of the period?25/150 = 0.17 = 17%

What is the period prevalence for the year?(25 + 15) / 150 = 0.27 or 27%

What is the point prevalence at the end of period?Not known

What is the cumulative incidence for the one year period?15/125 = 0.12 = 12%

FACTORS THAT INCREASE PREVALENCE

Cases move into population Healthy people leave population Longer living with disease Longer duration of disease Increased number of susceptible/at-risk individuals

FACTORS THAT DECREASE PREVALENCE

Cases move out of population Healthy people move into population People being cured Shorter duration of disease Decreased number of susceptible/at-risk

individuals

INTERRELATIONSHIP BETWEEN INCIDENCE AND PREVALENCE

Prevalence depends on both incidence and disease duration.

If the incidence is low but the disease duration is

long, the proportion of the population with

the disease at a particular time is high

compared to the incidence.

EXAMPLE OF INTERRELATIONSHIP

In the beginning of the AIDS epidemic, the incidence rate of AIDS increased quickly. However, the disease duration was short because everyone died in a few years. Therefore, the prevalence was low.

Incidence and duration = prevalence

EXAMPLE OF INTERRELATIONSHIP

Today, the incidence rate is not increasing as quickly but the duration of survival is considerably longer. Therefore, the prevalence is now much higher.

Incidence and duration = prevalence

PREVALENCE AND INCIDENCE

When the disease is stable:

Prevalence = Incidence * Disease Duration

Incidence vs. Prevalence

Incidence (I): Measures new cases of a disease that develop over a period of time.

Prevalence (P): Measures existing cases of a disease at a particular point in time or over a period of time.

Prevalence vs. Incidence

Prevalence can be viewed as describing a pool of disease in a population.

Incidence describes the input flow of new cases into the pool.

Fatality and recovery reflects the output flow from the pool.

SUMMARY

Risk (cumulative incidence) is the probability that an event will occur within a given time-interval

Rate (incidence rate) is a measure of how rapidly the events occur in a population

In contrast to measures of incidence (risk and rate), prevalence deals with existing (as opposed to newly occurring) health-related states

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Linelist: Example