Presentation on theme: "Surveillance of human disease: potentials and pitfalls NWZG July 2012 Dr Alex G Stewart (with help from Dr Sam Ghebrehewet and Dr Evdokia Dardamissis)"— Presentation transcript:
Surveillance of human disease: potentials and pitfalls NWZG July 2012 Dr Alex G Stewart (with help from Dr Sam Ghebrehewet and Dr Evdokia Dardamissis) Cheshire and Merseyside Health Protection Unit
Salmonella bareilly 2010 Farrington algorithm: no overall exceedance for Salmonella
Population health protection Communicable diseases, Environment, Emergency Planning Nature of pathogens/hazards Microbiology, transmission, pathology Toxicology, haematology, environmental sciences HPA structures surveillance Public health response to cases of specific diseases Disease prevention (through immunisation) Public Health Function Wider workforce, healthy settings, policy development Surveillance: foundational
Objectives of Surveillance If you cant explain it simply, you dont understand it well enough. Albert Einstein (Physicist, 1879–1955)
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)
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)
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) Langmuir, A The surveillance of communicable disease of national importance. New England Journal of Medicine 268: 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)
Principlesof 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
Sources You wont be surprised that diseases are innumerable count the cooks. Seneca (Philosopher, 4 BC – 65 AD)
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
Sources of data: Clinicians Laboratories Sentinel General Practices Child health Departments in PCTs Schools, Nursing / residential homes Maternity units Local Health Protection Units Regional Units Special surveys National Centre for Infections
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
Collection Not everything that counts can be counted, and not everything that can be counted counts. Albert Einstein (Physicist, 1879–1955)
Generic surveillance system Database Laboratory/clinic Data Analysis PCTs/SHA Health practitioners Policy makers SpecialistLaboratory Wide dissemination Supplementary data
Types of Surveillance Active (outbreak, lab) Passive (normal) Sentinel (flu) Based on secondary data analysis (HES)
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 statisticsthey 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.
Data collection problems MORTALITY legally required accuracy / limited outcome not reflect incidence & prevalence multiple causes delays in data
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
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
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)
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
Interpretation of data Whats 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
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 Routine surveillance: the reporting pyramid (Wheeler JG et al, BMJ 1999; 318: ) Acute, self-limiting, no mortality, common TB? Meningococcal disease? Ebola?
Why is surveillance important?
Data for 2002 is preliminary - as the number of reports rise, estimates of infants becoming HIV-infected will fall. Surveillance: Effectiveness of Interventions Introduction of universal antenatal HIV testing in 1999
Actions The man who insists on seeing with perfect clearness before he decides, never decides. Henri-Frederic Amiel (Philosopher, 1821–1881)
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
Evaluation of systems Life can only be understood backwards, but it must be lived forwards. Soren Kierkegaard (Philosopher, 1813–1855)
Evaluation of Epidemiological Surveillance systems Is it simple flexible acceptable sensitive representative timely DID IT RESULT IN ACTION? WHAT WAS DONE? WHO DID IT? ?
Potentials Develop analyses Olympics Improved links between systems animal surveillance Improved surveillance of chemical exposure non infectious incidents
There are three kinds of epidemiologist: those who can count and those who cant. Anonymous ( adapted by John M. Cowden, Emerg Infect Dis