Communicable Disease Control: Surveillance - National and International - its evaluation and use

This section covers:

• Surveillance - national and international - its evaluation and use

• Definitions
• Purpose of Surveillance
• Principles of surveillance
• Categories of surveillance
• Sources of surveillance data
• Sources of specific surveillance data
• Other types of data used for surveillance
• Evaluation of a Surveillance System

Definitions

Surveillance is 'the continued watchfulness over the distribution and trends in the incidence of disease through the systematic collection, consolidation and evaluation of morbidity and mortality reports and other relevant data'

(Alexander Langmur, founder of Centers for Disease Control and Prevention, Atlanta, USA 1960)

Many authorities also include data interpretation, information dissemination, and investigation and control measures in their definition of surveillance.

Surveillance is the 'on-going scrutiny, continuous analysis, interpretation and feedback of systematically collected data, generally using methods distinguished by their practicability, uniformity and frequently, their rapidity, rather than complete accuracy'.

(Last JM. A Dictionary of Epidemiology. New York: Oxford University Press, 1998.)

• predominantly descriptive statistics but also includes analytic epidemiology in outbreak investigations
• plot data from one or more sources over time to show trends
• correlation or inverse correlation suggest direct or inverse association
• main building blocks - counts, proportions, rates (and appropriate confidence intervals)

Purpose of Surveillance

• Allows individual cases of infection to be identified
• Measures incidence of infectious disease, with changes potentially indicating an outbreak
• Tracks changes in occurrence and risk factors of an infectious disease allowing targeted interventions
• Evaluation of existing control measures
• Detect emergence of new infections of public health importance

Principles of surveillance

• A good surveillance system requires a case definition which includes clinical and / or microbiological criteria
• Systematic collection of data: systematic, regular and uniform
• Analysis of data to produce statistics: by time, place and person
• Interpretation of statistics to provide information: but care needed with timeliness, completeness, representation
• Distribution of this information to those who require it for action. Feedback is via Health Protection Report http://www.hpa.org.uk/hpr/ information services, internet information sites e.g. Health Protection Agency (HPA), Department of Health publications, the Epinet System (Epinet uses a dedicated telephone link via computer modem. It uses message alerting and teletext to relay communicable disease alerts to primary care trusts to cascade outbreak alerts and transfer files)
• Continuing surveillance to evaluate action

Categories of surveillance

Active surveillance

• special effort to collect data and confirm diagnoses to ensure more complete reports, such as surveys and outbreak investigations
• encompasses formal and informal communications (such as phone calls to seek information)

Passive surveillance

• use of routine sources of information such as notifications, laboratory reports, Health Episode Statistics (HES)

Sentinel surveillance

• sample surveillance (HCAI Surveillance such as MRSA bacteraemias)
• 2 types:
  • geographic: reporting sources shown at specific sites
  • high risk groups: drug users etc

Sources of surveillance data

• Statutory notifications
• Laboratory reports
• Royal College of General Practitioners sentinel reporting system (Network of general practices that collect data on consultations / episodes of illness, especially useful for surveillance of conditions like influenza)
• Hospital Episode Statistics (HES) data
• Death certificates (limited use because few infectious diseases lead to death in 21st century Britain)
• Enhanced Surveillance for infections of public health importance to combine epidemiological and microbiological data e.g. meningococcal disease, TB
• Vaccine use (COVER statistics)
• Sickness absence
• Special systems: KC60 returns (for Sexually Transmitted Diseases (STD's), clinical HIV reporting which is voluntary to CDSC, British Paediatrics Surveillance Unit, Creutzfeldt-Jakob Disease (CJD) Surveillance unit

Sources of specific surveillance data

Influenza ('flu')

• HPA Colindale Surveillance of Influenza Group.
• Royal College of General Practitioners (RCGP) weekly returns service (principle measure of flu activity)
• Medical Officers of Schools Association (MOSA) scheme
• NHS Direct
• mortality data
• laboratory reports
   
  For more information see
  http://www.hpa.org.uk/infections/topics_az/influenza/seasonal/uk_data_sources.htm

Tuberculosis (TB)

• statutory notifications
• Enhanced Tuberculosis Surveillance - ETS (since 1999)
• Treatment Outcome surveillance - part of ETS
• Mycobnet - microbiological network for TB surveillance to monitor drug resistance
• Laboratory reports
• Death certificates
• TB incident and outbreak surveillance (TBIOS)

Nosocomial Infection

• Health Episode Statistics (HES) / Patient Administration Systems (PAS)
• nursing, doctor, Intensive Therapy Unit (ITU) notes
• procedures register
• laboratory reports
• Enhanced surveillance - MRSA bacteraemia, Clostridium difficile, Surgical site infections

HIV

• Voluntary reporting from PCT commissioners & hospital trusts
• Unlinked Anonymous Prevalence Monitoring Programme (UAPMP) - this programme aims to estimate the prevalence of HIV by making use of residual sera from routine samples taken for other tests and irreversibly unlinked from patient identifiers before testing e.g. samples taken in: Genito-Urinary Medicine (GUM) and IV drug user clinics, antenatal specimens.
• Laboratory reports
• Annual SOPHID survey (Survey of known HIV positive patients who attend for HIV related case in a year
• HIV sera-surveys done on blood donors in general hospitals
• Behaviour surveys
   
  For more information see
  http://www.hpa.org.uk/infections/topics_az

STIs

• KC60 returns data
• Laboratory reports
• Hepatitis B
• Antenatal screening data
• Blood donors
• Voluntary surveillance of people at IV drug users and Genito-Urinary Medicine (GUM) clinics
• Zero prevalence surveys

Other types of data used for surveillance

• census data
• health service utilisation reports
• epidemic reports
• animal reservoir and vector studies
• disease registers

Evaluation of a Surveillance System

- similar considerations are also used when establishing a surveillance system

Steps to be taken when evaluating a surveillance system:

1. Describe the public health importance of the health event under surveillance; consider:
   • total number of cases, incidence and prevalence
   • indices of severity (death rate, case fatality ratio)
   • Can it be prevented?
2. Describe the surveillance system to be evaluated
   • List its objectives, for example:
   • detecting and monitoring outbreaks
   • detecting and monitoring trends
   • setting priorities and allocating resources
   • describe the health event under surveillance
   • state the case definition
   • state the population
   • draw a flow chart of the system
   • describe the components and operation of the system
   • what information is collected
   • who collects the data
   • time to collect data
   • mode of data transfer and storage
   • who analyses data
   • how is the data disseminated
   • who is it disseminated to
3. Discuss validity and repeatability of case definitions in various types of surveillance data
4. Indicate the level of usefulness by describing the actions taken as a result of data collected by the surveillance system. (e.g. useful in prevention and control of adverse event).
   • what actions are taken because of the data
   • who uses data to initiate action
   • list anticipated uses of data
5. Describe cost / resources needed to run surveillance
   • indirect
   • direct: data collection/analysis/interpretation and dissemination
6. Evaluate the quality of the surveillance system by assessing its attributes
   

   	Key attributes of a surveillance system:
   	simplicity flexibility acceptability: to public/data collectors sensitivity: ability to detect health events timeliness representativeness: does it accurately describe incidence of health events in population by time/place/person.
   	Other attributes of a surveillance system:
   	completeness consistency importance

7. List conclusions and recommendations
   • Is the system meeting its objectives?
   • address the need to continue/modify surveillance
   • NB: no system perfect; trade-offs must always be made

Ways to improve the system:

• improve awareness of disease by increasing education
• simplify reporting
• frequent feedback
• use multiple sources and methods
• active surveillance
• sentinel surveillance
• computerisation

© Sarah Anderson, Gayatri Manikkavasagan 2008