| Surveillance: What is it and Why do we do it? |
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Module 1: VICNISS online self guided surveillance education
To download this module and/or the associated multiple choice exercises as PDF files, click on
Education Resources.)
Module Menu
Overview
This module gives an overview of surveillance and in particular, its purpose in healthcare settings.
Objectives
After you have completed this module you should be able to:
- Explain what health surveillance is and why we do it;
- Identify the basic elements of public health surveillance; and
- Identify the important factors to be considered when choosing your surveillance activities.
Defining Surveillance
In the health setting, surveillance can be defined as: the systematic collection, management, analysis, interpretation and reporting of
data for use in the planning, implementation and evaluation of health practice. Data obtained from surveillance
(for example, of infectious diseases) can help us determine many public health activities, such as prevention and control.
Surveillance of infectious diseases has been practiced in various forms for many centuries. The earliest public health actions
probably related to movement restrictions placed on persons during periods of bubonic plague. Systematic disease surveillance,
however, had to await the development of classification systems for disease and illness and organised health care infrastructure.
Most countries now have disease reporting systems including national disease-monitoring activities. The importance of ongoing
surveillance for new and emerging diseases was emphasised very recently with the outbreak
of SARS.
The concept of health surveillance has now broadened from monitoring of infectious diseases to encompass chronic diseases, adverse
events, processes and injury. Within a hospital setting, information we obtain from surveillance of infections gives
us objective data through which we can aim to improve patient outcomes.
Why do we undertake Surveillance Activities?
Surveillance of diseases, conditions or events can give us reliable data on which
to base decisions. These data allow us to assess the situation, including the size
of the problem and trends over time, and can assist us in developing and evaluating
interventions. A good surveillance program should be able to:
Use of computers has and will continue to alter the way surveillance is carried
out. Sharing and transfer of information facilitates collection of data from many
sources, making surveillance easier, but also raises legal and ethical issues. Computers
also put statistical and epidemiological analysis within easy reach of the average
person. These changes will continue to influence the way we go about surveillance
in future. The challenge is to have a good understanding of the principles of surveillance
and to ensure our surveillance is scientifically valid, useful and thoroughly evaluated.
Selecting Surveillance Targets
We can’t possibly carry out surveillance on all health issues so how do we
choose? Within the hospital setting, we must tailor our surveillance activities
to best match resources with priorities and institutional objectives. The following
elements should be considered when choosing events for surveillance:
- The specific objectives of the surveillance system, i.e. what exactly do you want to know?;
- The frequency of the event;
- The cost or impact of the event;
- The potential for surveillance data to contribute to prevention activities;
- The health needs of the client or patient population; and
- The organisation’s mission and strategic goals.
Traditionally, surveillance for nosocomial infections was often “hospital-wide”
surveillance, where data were collected on all identified infections in the facility.
This method of surveillance has now largely been overtaken by more targeted surveillance
methods, which focus on at-risk groups. The advantages and disadvantages of these
two surveillance methods for nosocomial infections are summarised in Table 1.
Table 1
Advantages and Disadvantages of Two Major Surveillance Strategies for Nosocomial
Infections
| Method |
Advantages |
Disadvantages |
| Traditional hospital wide surveillance |
Collects comprehensive data on all infections in the facility.
Establishes baseline infection rates.
Identifies patterns of infections.
Recognises outbreaks early.
Increases visibility of ICP.
Identifies the scale of the problem within the hospital
|
Expensive, labour intensive, and time-consuming.
May yield excessive data.
With limited resources, may leave insufficient time to analyse data and initiate changes.
Some infections detected cannot be prevented.
Overall infection rate not valid for inter-hospital comparison.
If high infection rates are detected, it may not be clear where the problems are occurring
|
| Priority-directed site-specific surveillance |
Resource based methodology - flexibility and adaptability for specific needs and problems.
Can focus on infections with known control measures to reduce infection risk.
Can determine valid denominators.
For some measurements, availability of appropriate risk adjustment systems and external comparative data.
|
Collects data only for targeted patients or risks - limited information about endemic rates.
May miss clusters or outbreaks in non-surveyed areas or populations
|
Think about your current surveillance activities. Why have these areas been chosen?
Are there other areas that you think you should be covering?
The Surveillance Cycle
The process of surveillance is often referred to as “the surveillance cycle”.
This emphasiaes the fact that the data collected are collated, analysed, interpreted
and importantly, communicated to those who can take action if this is necessary.
In a hospital setting, data and information may routinely be fed back to a number
of groups including infection control staff, surgeons and administrators. A good
surveillance program requires the cooperation and contribution of many individuals
and feedback is a vital part of maintaining this as well as achieving improvements
in both surveillance and outcomes.
1. Data Collection
To ensure good reliable data, the information being collected must be well defined
and understood by all those involved. In any surveillance system therefore, it is
important to clearly define both the events and the population under surveillance.
For nosocomial infection surveillance where outcomes are being measured, the
event is usually an infection. A population under surveillance may be all patients
who had a hip replacement in July and who spent 24 hours or more in hospital. Definitions
of what constitutes a nosocomial infection may vary, however the Centers for Disease
Control (CDC) National Nosocomial Infection Surveillance System (NNIS) definitions
are the most comprehensive and widely used definitions for nosocomial infections.
The use and correct application of these definitions is important if the results
of surveillance are to be compared between facilities and internationally.
Examples of types of data that are commonly collected for nosocomial infection surveillance include;
- Patient demographics;
- Clinical information about an infection;
- Laboratory data;
- Risk factors (relating to patient and procedures); and
- Interventions.
All data collected should be relevant and useful, and the surveillance kept as simple
as possible to avoid inefficient use of resources. It is often necessary to strike
a balance between collecting all the information necessary for analysis and reporting
and the amount of time and effort required to collect this information.
Case Finding
It is important to choose methods of finding infections that are able to find as
many relevant infections as possible. These are known as sensitive methods of case
finding. As an extreme example, you could examine every patient’s medical records
for any indication of an infection. Even this method may not find every case, but
equally importantly it may also result in some “false positives” i.e.
infections may be attributed to people who did not have a nosocomial infection.
Methods such as this can also mean a lot of time and effort is spent collecting
irrelevant data.
To minimise these problems, methods of case finding for infections must also be
specific, in that they find only true cases of infection and minimise false positives.
A highly sensitive method is often not highly specific and vice versa.
It can be difficult to find a method of case finding which is both sensitive and
specific, and this usually involves using more than one source of data and information.
Many different sources may provide information about nosocomial infections .
This may include patient based sources such as medical records, clinical rounds
and communication with staff; laboratory based sources such as pathology reports
and antimicrobial susceptibility patterns and other departments such as Admissions,
the Operating Suite and Outpatient clinics.
Test your Knowledge - Exercise 1
Clicking the above link will take you to the Education Resources page where you can download a PDF version of the Exercises Questions and Answers
Examples of case finding methods are given in Table 2, with an estimate of the sensitivity of each method. Sensitivity is estimated on a scale of 0 to 1, with larger numbers indicating
a more sensitive method of case finding which is likely to find most cases, but
may be time consuming and may involve reviewing significant numbers of “non” cases as well.
Post discharge surveillance is of increasing concern because of shorter lengths
of stay in the acute care inpatient setting. Although there are no standardised
methods for this kind of surveillance, development of such systems is becoming increasingly
important as without post discharge surveillance a significant percentage of infections
may be missed. Post discharge surveillance is not currently included in VICNISS.
Table 2
Case Finding Methods
| Method |
The Data Source Reviewed |
Sensitivity* |
Estimated Time
(Hours)/500 Beds** |
| Total Chart Review |
Review all patient medical records |
0.74-0.94 |
35.7-53.6 |
| Selective Medical Record Based On***: |
Only those medical records selected by screening: |
|
|
| Laboratory Reports |
Microbiology reports to identify patients with positive cultures |
0.77-0.91 |
23.2 |
| Kardex Screening |
Patient kardex to determine patients at high risk for infection |
0.75-0.94 |
14.3-22.3 |
| Fever |
Temperature record to identify patients with temperature >37.8ºC |
0.09-0.56 |
8 |
| Antibiotic Use |
Medication record to identify patients receiving antibiotics |
0.57 |
14.3 |
| Fever and Antibiotic Use |
Temperature record to identify patients with fever >37.8ºC, and medication
record to identify patients receiving antibiotics |
0.70 |
13.4 |
| Readmission |
Admission record for patients readmitted with infection |
0.08 |
Not specified |
| Autopsy Reports |
Autopsy reports to identify patients with infections |
0.08 |
0.53< |
| Ward Liaison Surveillance |
Patients reported by nursing staff to have an infection |
0.62 |
17.6 |
| Laboratory-based Ward Liaison Surveillance |
Microbiology reports to identify patients with a positive culture and patients reported
by nursing staff to have an infection |
0.76-0.89 |
31.8 |
| Risk Factor Based Surveillance |
Nursing reports and medication records to identify patients with risk factors for infection |
0.50-0.89 |
32.4 |
| Infection Control Sentinel Sheet System |
“Sentinel Sheet” to identify patients reported by nursing staff to have
symptoms of infection |
0.73 |
**** |
*Sensitivity of the case-finding method is reported for the number of nosocomial infections identified by the method but not for the
number of patients with nosocomial infections identified by the method.
**Number of hours per week required for an infection control professional to perform surveillance in a 500-bed hospital.
***If these data are in a computer database, infection control staff can review this information on the computer or can review
computer printouts.
****Case-finding method suitable for intensive care and specialty units; requires 1 minute per chart per day.
Adapted from Pottinger J.M, Herwaldt L.A and Perl T.M (1998).
2. Data Management
Data should be collected, organised and stored in systems that facilitate analysis
and reporting. Computerisation can greatly assist with this process. Efficient and
effective management of large amounts of data can require specialist skills and
computer hardware, and these are important considerations when designing surveillance
systems and collecting surveillance information.
3. Data Analysis
Surveillance systems need to incorporate appropriate analyses, usually not relying
on count data (eg. number of infections) alone, but using methods that that take
into account the size and constitution of the population, as well as the time period
of the surveillance. Within any population, individuals exhibit variation. These
differences may affect an individual’s risk of infection. For example, people
with diabetes or obesity may be at a higher risk of infection than people without
these conditions. When comparing populations, we often make attempts to adjust for
these factors to make the comparisons fairer or more valid.
Stratification is a technique to control for differences in distribution of risk
by subdividing a larger population into groups with similar attributes. For example,
surgical patients may first be grouped according to the type of surgery they have.
Following this they may be further divided into groups of patients at high, medium
and low risk of infection using a standard method. These types of stratification
allow separate infection rates to be calculated for each group and for fairer comparisons between
groups, for example between hospital or surgeon rates.
VICNISS uses the CDC NNIS basic risk index to divide groups of patients into those
with similar infection risk for most operative procedures. In this system the patient
is given one point for an ASA score of >=3, one point for a wound class that
is dirty or dirty/infected, and one point for a duration of operation that is longer
than the 75th percentile of the duration of operation for their operative procedure. The
lowest possible risk index is 0 and the highest is 3.
As an example, the NNIS 75th percentile for duration of operation for CABG surgery is 300 minutes,
which means that 75% of these operations take 300 minutes or less, and 25% of them
take longer than 300 minutes. Thus a person having a CABG procedure that takes 320
minutes is awarded one point. If that person also has an ASA >= 3 and a clean
wound their risk index would be 2.
Calculation of Infection Rates
The general formula for calculation of infection rates is:
Infection rates are often multiplied by a factor of 100 or 1000 and expressed as
the number of infections per 100 operations, for example. Device-associated infection
rates are often expressed as a rate per 1000 line days, for example 2.1 infections
per 1000 ventilator-days.
Comparison of rates for different time periods, for different hospitals, or, less
commonly between individuals, should only be attempted in the following circumstances:
- Where surveillance methods and definitions were uniform and consistently applied;
- Where rates have been calculated on groups stratified according to infection risk; and
- Where the sample size was sufficiently large to calculate a valid estimate of the infection rate (The required sample size
depends on what the rate is expected to be, and can be calculated).
Given that the 75th percentile for duration of operation for CAGS surgery is 300
minutes, calculate the basic risk index for the following CABG patients:
| Patient |
ASA score |
Wound class |
Procedure duration |
| Allan Jones |
3 |
Clean |
325 minutes |
| Ben Johnston |
2 |
Clean |
280 minutes |
| Jane Sykes |
4 |
Clean |
299 minutes |
| Alfred Einstein |
3 |
Clean |
400 minutes |
Test your Knowledge - Exercise 2
Clicking the above link will take you to the Education Resources page where you can download a PDF version of the Exercises Questions and Answers
Process Surveillance
The previous section detailed the basics of nosocomial infection surveillance where
infection rates are being directly measured. It is not always possible or desirable
to measure the number of infections, however, and an alternative method of surveillance
is to measure processes rather than outcomes. This often constitutes measuring compliance
with established practices which are known to contribute to lowering hospital acquired
infections. For example, obtaining data on the proportion of patients receiving
the recommended antibiotic prophylaxis before surgery.
Process surveillance can be useful in smaller hospitals or those which do not see
enough infections to enable rates to be calculated, or where sample sizes (usually
numbers of patients) are small.
Processes most suitable and useful for surveillance include those where good evidence
exists to demonstrate that they are closely linked to infection rates. For example,
the CDC Category 1A recommendations for the prevention of surgical site infections
that are “strongly recommended for implementation and supported by well designed
experimental, clinical or epidemiological studies.” These recommendations cover
patient preparation (treatment of pre-existing infections; hair removal), antimicrobial
prophylaxis, and aseptic technique for placement of intravascular devices.
4. Feedback and Reporting
The results of all analyses must be communicated to the persons who need the information
and have the power to authorise changes. There is little point in carrying out surveillance
if the data are not used to report on rates and to make changes where these are
necessary. It is said that surveillance without action is a waste of time. Regular
reporting and feedback is a vital component of a successful surveillance system.
Reports and feedback should also be useful to those reading them and allow them
to draw conclusions and take action.
Planning your Surveillance Activities
When carrying out surveillance, it is useful to have a long term plan to ensure
that the data collected will meet your requirements. When developing a surveillance
plan for your facility the following key questions should be addressed:
- What are the priorities for nosocomial infection surveillance?
- How will the data be used?
- What patients should be included?
- Certain high-risk patients.
- Patients undergoing certain operative procedures OR who are exposed to certain high-risk procedures.
- Patients in certain areas of the hospital.
- What kinds of data are needed?
- Data primarily on infections and their characteristics.
- Data on the populations who are at risk.
- Data that will permit the calculation of infection rates by risk index.
- Data that will permit the calculation of device-associated infection rates.
- What time period should the data cover to provide the most useful information, eg.
one month; periodic intervals during the year; quarterly, semi-annually or annually;
or continuous.
- What resources are required?
- How much and what kind of resources are needed to fulfil the requirements of the
surveillance components and to collect additional data of interest?
- Personnel (Surveillance, clerical, data processing, other department).
- Data sources, including both laboratory and patients records.
- Information technology.
Careful consideration of these issues should ensure that the data and the resulting
analyses fulfil the purpose for which they were collected.
Test your Knowledge - Exercise 3
Clicking the above link will take you to the Education Resources page where you can download a PDF version of the Exercises Questions and Answers
Further Information: