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Surveillance of human disease: potentials and pitfalls

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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

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