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Surveillance of human disease: potentials and pitfalls

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

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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. 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) HPA structures Nature of pathogens/hazards Microbiology, transmission, pathology Toxicology, haematology, environmental sciences surveillance Surveillance:foundational

  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. 1963. The surveillance of communicable disease of national importance. New England Journal of Medicine268:182-192

  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 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 Diseases notifiable (to Local Authority Proper Officers) under the Health Protection (Notification) Regulations 2010 Typhus Viral haemorrhagic fever (VHF) Whooping cough Yellow fever http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/NotificationsOfInfectiousDiseases/ListOfNotifiableDiseases/

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

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

  27. Why is surveillance important?

  28. 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.

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

  30. 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

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

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

  33. http://www.ics.uci.edu/~eppstein/pix/dianafall04/mitch/Holes-m.jpghttp://www.ics.uci.edu/~eppstein/pix/dianafall04/mitch/Holes-m.jpg Potentials • Develop analyses • Olympics • Improved links between systems • animal surveillance • Improved surveillance of chemical exposure • non infectious incidents

  34. 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. 2010 http://wwwnc.cdc.gov/eid/article/16/1/09-0030.htm)

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