1. Surveillance of human disease: potentials and pitfalls
Dr Alex G Stewart
(with help from Dr Sam Ghebrehewet and Dr Evdokia Dardamissis)
Cheshire and Merseyside Health Protection Unit
NWZG
July 2012

2. Salmonella bareilly 2010 Farrington algorithm:
no overall exceedance for Salmonella

3. Surveillance: foundational
Public Health Function
Wider workforce, healthy settings, policy development
Population health protection
Communicable diseases, Environment, Emergency Planning
Public health response to cases of specific diseases
Disease prevention
(through immunisation)
Building blocks of the module
Nature of pathogens/hazards
Microbiology, transmission, pathology
Toxicology, haematology, environmental sciences
surveillance
HPA
structures

4. Objectives of Surveillance
“If you can’t explain it simply, you don’t understand it well enough.”
Albert Einstein (Physicist, 1879–1955)

5. Objectives of surveillance
detecting acute changes (outbreaks / epidemics)
identifying & quantifying patterns (increased STIs)
observing changes in agents and hosts (‘Flu)
detecting changes in health practice (C Section)
disease investigation & control (meningitis)
health service planning (births, TB)
evaluation of prevention / controls (HIV in pregnancy)
study natural history / epi of disease (Cx cancer)
provide info & baseline data (eradication of measles)

6. Principles & Practice
“It is the mark of an educated mind to rest satisfied with the degree of precision which the nature of the subject admits and not to seek exactness where only an approximation is possible.”
Aristotle (Philosopher, 384–322 BC)

7. Epidemiological Surveillance
Definition:
‘Collection, collation & analysis of data & prompt dissemination of information to those who need to know so that action can result’ (Langmuir, 1963)
Action further specified by CDC, Atlanta as ‘planning, implementation, and evaluation of public health practice’
To enable action, surveillance should be ‘ongoing, practicable, consistent, timely and have sufficient accuracy and completeness’ (Comm Dis Ctrl Handbook, p246)
Langmuir, A The surveillance of communicable disease of national importance. New England Journal of Medicine 268:

8. Principles of surveillance
systematic collection of data
analysis of data to produce statistics
interpretation of statistics to provide intelligence
distribution of intelligence to those who will act
continuing surveillance to evaluate action

9. Sources
“You won’t be surprised that diseases are innumerable — count the cooks.”
Seneca (Philosopher, 4 BC – 65 AD)

10. Communicable disease surveilance
1801 Census
1891 London
(cholera diphtheria smallpox typhoid)
1899 E&W
1984 Public Health [Control of Disease] Act & associated regulations (Drs)
2008 Health and Social Care Act & associated regulations (HCW)
2012 Verbal reports accepted

11. Acute infectious hepatitis Anthrax Botulism Brucellosis Cholera
Diseases notifiable (to Local Authority Proper Officers) under the Health Protection (Notification) Regulations 2010
Acute encephalitis
Acute meningitis
Acute poliomyelitis
Acute infectious hepatitis
Anthrax
Botulism
Brucellosis
Cholera
Diphtheria
Enteric fever (typhoid or paratyphoid)
Food poisoning
Haemolytic uraemic syndrome (HUS)
Infectious bloody diarrhoea
Invasive group A streptococcal disease & scarlet fever
Legionnaires’ Disease
Leprosy
Malaria
Measles
Meningococcal septicaemia
Mumps
Plague
Rabies
Rubella
SARS
Smallpox
Tetanus
Tuberculosis
Typhus
Viral haemorrhagic fever (VHF)
Whooping cough
Yellow fever

12. Sources of data: Schools, Nursing / residential homes Clinicians
“Sentinel” General
Practices
National Centre
for Infections
Local Health
Protection Units
Regional
Units
Maternity units
Laboratories
Child health
Departments in PCTs
Special surveys

13. “Enhanced” surveillance
Information from notifications & lab reports minimal:
name
address
disease/organism
onset (notification)
More information collected on certain diseases
Tuberculosis
Meningococcal disease
Hepatitis B

14. Collection
“Not everything that counts can be counted, and not everything that can be counted counts.”
Albert Einstein (Physicist, 1879–1955)

15. Generic surveillance system
Wide dissemination
Laboratory/
clinic
Policy makers
PCTs/SHA
Health practitioners
Database
Supplementary data
Data Analysis
Specialist
Laboratory

16. Based on secondary data analysis (HES)
Types of Surveillance
Active (outbreak, lab)
Passive (normal)
Sentinel (flu)
Based on secondary data analysis (HES)

17. Collection – ensure: quality, uniformity & reliability
Definitions (standard, specific, simple, acceptable, understandable)
Ease of collection (simple, clear, unambiguous, imp only)
Timeliness (pre-specified: daily, weekly…)
Completeness (missing data)
Motivation (legal requirements / education incentives)

18. Advantages and disadvantages
Problems
Advantages and disadvantages

19. Josiah Charles Stamp Economist, 1880–1941
‘When you are a bit older’ a judge in India once told an eager young British civil servant, ‘you will not quote Indian statistics with that assurance. ‘The government is very keen on statistics—they collect them, add them, raise them to the nth power, take the cube root and prepare wonderful diagrams. ‘But what you must never forget is that every one of those figures comes from the chowkidar, or village watchman, who just puts down what he damn pleases.’

20. Data collection problems
MORTALITY
legally required
accuracy / limited outcome
not reflect incidence & prevalence
multiple causes
delays in data

21. Data collection problems
MORBIDITY
legally required (<1984 fee ?prosecution)
professional duty (>2008)
good for severe & rare diseases
biased to acute infections
timeliness
under-notification of common diseases
over-notification due to inaccurate diagnosis
definitions

22. Data collection problems
LAB REPORTS
accurate diagnosis
info on organisms & toxins easy but disease?
not reflect incidence and prevalence
accuracy of test
limited epi info

23. Analysis & Interpretation
“If it looks like a duck, and quacks like a duck, we have at least to consider the possibility that we have a small aquatic bird of the family Anatidae on our hands.”
Douglas Adams (Science fiction writer, 1952–2001)

24. Analysis of data
Person – age, sex, level of immunity, nutrition, lifestyle, occupation / school, hospitalisation, SES, risk factors, smoking alcohol…
Place - localised outbreaks, location or source of disease or person at time of infection, helps define risk groups (denominator)
Time – number reported / week; by season; long term trends

25. Interpretation of data What’s going on Is change true?
Population changes (denominator)
Improvement in diagnosis
Better awareness / reporting
Report duplication / change of system (case def.)
Context
Evaluate control measures
Identify new disease and infectious agents

26. Routine surveillance: the reporting pyramid (Wheeler JG et al, BMJ 1999; 318:1046-50)
136 cases of infectious intestinal
illness in the community
23 present to GP
6 stools submitted
to the laboratory
1.4 positive
lab result
1 reported
to surveillance
Acute, self-limiting, no mortality, common
TB? Meningococcal disease? Ebola?

27. Why is surveillance important?

29. Introduction of universal antenatal HIV testing in 1999
Surveillance: Effectiveness of Interventions
Introduction of universal antenatal HIV testing in 1999
Data for 2002 is preliminary - as the number of reports rise, estimates of infants becoming HIV-infected will fall.

31. Actions
“The man who insists on seeing with perfect clearness before he decides, never decides.”
Henri-Frederic Amiel (Philosopher, 1821–1881)

32. Actions with intelligence
Communication, communication, communication!
Good & regular feedback to data collectors
Regular reports:
With good distribution to interested & involved persons
Professionals (newsletters, reports, journals)
Public (prevention, diagnosis, treatment news)
Policy / decision makers

33. Evaluation of systems
“Life can only be understood backwards, but it must be lived forwards.”
Soren Kierkegaard (Philosopher, 1813–1855)

34. Evaluation of Epidemiological Surveillance systems?
Is it
simple
flexible
acceptable
sensitive
representative
timely
DID IT RESULT IN ACTION?
WHAT WAS DONE?
WHO DID IT?

35.
Potentials
Develop analyses Olympics Improved links between systems animal surveillance Improved surveillance of chemical exposure non infectious incidents

36. That’s it, folks! “There are three kinds of epidemiologist:
those who can count and those who can’t.”
Anonymous (adapted by John M. Cowden, Emerg Infect Dis