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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

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
Salmonella bareilly 2010

Farrington algorithm:

no overall exceedance for Salmonella

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)

HPA

structures

Nature of pathogens/hazards

Microbiology, transmission, pathology

Toxicology, haematology, environmental sciences

surveillance

Surveillance:foundational
objectives of surveillance

Objectives of Surveillance

“If you can’t explain it simply, you don’t understand it well enough.”

Albert Einstein (Physicist, 1879–1955)

objectives of surveillance1
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

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
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

principles of surveillance
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
sources

Sources

“You won’t be surprised that diseases are innumerable — count the cooks.”

Seneca (Philosopher, 4 BC – 65 AD)

communicable disease surveilance
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
slide11
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/

sources of data
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

enhanced surveillance
“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

Collection

“Not everything that counts can be counted, and not everything that can be counted counts.”

Albert Einstein (Physicist, 1879–1955)

slide15

Laboratory/

clinic

Supplementary data

Specialist

Laboratory

Data Analysis

Generic surveillance system

Wide dissemination

Policy makers

PCTs/SHA

Health practitioners

Database

types of surveillance
Types of Surveillance
  • Active (outbreak, lab)
  • Passive (normal)
  • Sentinel (flu)
  • Based on secondary data analysis (HES)
collection ensure quality uniformity reliability
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)
problems

Problems

Advantages and disadvantages

josiah charles stamp economist 1880 1941
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.’
data collection problems
Data collection problems
  • MORTALITY
  • legally required
  • accuracy / limited outcome
  • not reflect incidence & prevalence
  • multiple causes
  • delays in data
data collection problems1
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 problems2
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

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
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 what s going on is change true
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
routine surveillance the reporting pyramid wheeler jg et al bmj 1999 318 1046 50

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?

slide29

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.

actions

Actions

“The man who insists on seeing with perfect clearness before he decides, never decides.”

Henri-Frederic Amiel(Philosopher, 1821–1881)

actions with intelligence
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

Evaluation of systems

“Life can only be understood backwards, but it must be lived forwards.”

SorenKierkegaard (Philosopher, 1813–1855)

evaluation of epidemiological surveillance systems
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

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
slide36

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)