Transcript Global Public Health

BIO4503 APPLIED EPIDEMIOLOGY
MONITORING AND
SURVEILLANCE IN
EPIDEMIOLOGY
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Dr. Carmen Aceijas, PhD
Lecture description
• PUBLIC HEALTH SURVEILLANCE. DEFINITION AND
MAIN FEATURES
• CASE DEFINITION FOR SURVEILLANCE SYSTEMS
• TYPES OF PH SURVEILLANCE
• USE OF SURVEILLANCE SYSTEMS
• DATA FOR SURVEILLANCE SYSTEMS
DEMOGRAPHIC DATA
MORTALITY DATA
MORBIDITY DATA
PUBLIC HEALTH SURVEILLANCE
• PH Surveillance: “Systematic, continuous monitoring of the
incidence and transmission of a disease”
• WHO Public health surveillance site:
http://www.who.int/topics/public_health_surveillance/en/
• Most countries have systems in place to monitor certain
diseases [e.g.: meningitis, anthrax and TB]. They operate
through mandatory reporting of cases [NOTIFIABLE
DISEASES].
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– Mandatory for all health providers involved in the detection of cases
– Reporting of cases [number]
– Reporting of risk factors also included [e.g.: smoking, alcohol
consumption]
PUBLIC HEALTH SURVEILLANCE. CASE
DEFINITION FOR SURVEILLANCE
SYSTEMS
• Surveillance systems to be efficient require
strict criteria and standard methods.
• Criteria for case definition:
– 1. clinical findings
– 2. laboratory results [to confirm/reject clinical
diagnosis]
– 3. epidemiological data describing time, place
and type of individuals affected
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PUBLIC HEALTH SURVEILLANCE.
TYPES OF PH SURVEILLANCE
• PASSIVE
- Reporting of cases in automatic and routine
• ACTIVE
- Rarely carried out routinely
- Uses periodic visits to institutions [e.g.: hospitals] to collect
required data.
- Used to monitor the spread of a new disease or outbreak
- Costly and labour intensive
Limitations of any surveillance system: sensitivity is not 100%.
Therefore, estimates are conservative.
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WHAT DOES PUBLIC HEALTH
SURVEILLANCE ALLOWS US TO MEASURE?
• BASELINE
- Routine monitoring allows the determination of what is “normal”
in a given population regarding the spread [incidence rates] of
a given disease.
- Affected by changes in case definition and/or data collection
methods
• TIME TRENDS
- Focus on variations in disease incidence.
- Useful to:
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- Identify outbreaks
- Measure variations in the disease incidence over time [time trends]
- Assess impact of PH interventions [e.g.: effect of vaccination policies]
WHAT DOES PUBLIC HEALTH
SURVEILLANCE ALLOWS US TO MEASURE?
(II)
• TIME TRENDS [cont]
Reliability of measurements affected by:
- Awareness of a condition leads to increase of reporting
- In post-outbreak times, health professionals will tend to
detect more cases [case-ascertain bias].
• PATTERNS OF DISEASE
E.g.: Seasonal variations observed in cardiac mortality
winter: higher mortality
winter + older age: higher mortality
Specific disease patterns must be incorporated in the baseline
calculations.
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DATA FOR SURVEILLANCE
SYSTEMS
• Demographic data
• Mortality data
– Completeness of mortality statistics
– Health indices derived from mortality data and
other uses
• Morbidity data
– Communicable diseases
– health centres and hospital data
– other sources of morbidity data
Demographic data
• Demographic data is routinely collected at country level in
the census [UK is every 10 years]
• Type of indicators included: sex, age, geographical
distribution, ethnicity, religion, level of education and so
on
• Annual statistical projections are also carried out [in UK by
the Office for National Statistics [ONS]]
• ONS also implements the continuous multipurpose survey
“General Household Survey” [GHS] which collects
information on a rather wide range of demographic
aspects of our society [e.g.: employment, education,
sports and leisure engagement]
Demographic data [cont.]
• Demographic data is essential to understand the real impact of
diseases and the resources available to tackle them.
– E.g.: The impact of 1,000 cases of newly diagnosed TB is
very different in a 1,000,000 population compared to
10,000,000 population. Why?
– E.g.: 1,000 new cases of TB represent a very different
challenge in a well established health service compared to a
newly established system. Why?
– E.g.: 1,000 new cases of TB in a high GDP population is
very different than in a low GDP population. Why?
Where to find population data
• Go to: http://www.who.int/countries/en/
• In pairs, chose a country and decide what
demographic indicators of those available
you would like to use for a “newly established
surveillance system” in that country for a
health disease of your choice
• ½ max hour exercise
Mortality data [I]
• Data on mortality is collected at country level
via death certification.
• Data on mortality is used for health analysis as
it is a good proxi indicator of the health of a
population and the main diseases affecting it.
• In UK, NOS is the body who provides with the
guidelines to medical doctors to fill in the
“medical certificate of cause of death” . There
are three main types of certificates: stillbirth,
neonatal and others.
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Mortality data [II]
• Routine mortality statistics require that for each death a single cause
of death is identified.
• WHO’s guidance on it is:
– The disease or injury that initiated the train of events leading to
death.
– The accident or violence that produced the fatal injury/ies
• However, other significant [to the death] health issues will be recorded
as well.
• The International classification of disease [ICD] is used to assign a
single code to each possible cause of death. ICD is a standard
diagnostic tool for epidemiology, health management and clinical
purposes.
• The
ICD
10
[current
version]
can
be
accessed
at:
http://www.who.int/classifications/icd/en/
• WHO collates country data to produce the analysis of deaths by sex,
age group and cause of death.
Completeness and accuracy of
mortality statistics
• Completeness refers to the proportion of all deaths that are registered.
Developed countries register all deaths but this not the case for many
developing countries.
• Additionally, accuracy can be compromised by things such errors in the
clinical diagnosis, errors in filling in the certificate or errors in ICD code
assignment.
• Factors affecting poor reporting:
– Infrastructure [e.g.: fewer medical doctors and hospitals in rural areas]
– Religious and cultural beliefs [e.g.: some countries refuse to
acknowledge they have HIV/AIDS within their borders]
– country specifics: some countries include deaths of nationals abroad as
their own statistics.
– A way to ascertain problems in completeness of reporting: to divide
annual deaths reported by total deaths estimated for the whole
population
Mortality data and health indices
• Mortality data is also calculated to calculate a
number of health indicators.
• E.g.: neonatal and infant mortality is used as
an index of general health and the provision
of care for a large population.
• Other routinely collected indicators fed by
mortality information are maternal health and
standardized mortality ratios.
MORBIDITY DATA
• We need to know the burden of disease
[both from communicable and NCD] to
plan services and to provide the basic
information for epidemiological and
clinical research [to formulate research
questions on the possible determinants of
diseases].
MORBIDITY DATA. COMMUNICABLE
DISEASES [I]
• Data on communicable diseases are collected and
reported by public health agencies.
• In UK the list of notifiable diseases [n=30] is published
by
PHE.
It
can
be
accessed
at:
http://www.hpa.org.uk/Topics/InfectiousDiseases/Infec
tionsAZ/NotificationsOfInfectiousDiseases/ListOfNotifi
ableDiseases/
• Doctors are required by law to notify both suspected
and confirmed cases of notifiable diseases.
MORBIDITY DATA. COMMUNICABLE
DISEASES [II]
• WHO plays a key role in monitoring outbreaks of
communicable diseases.
• The international agreement for the monitoring of
communicable diseases was achieved in 1951 under the name
of “International Sanitary Health Regulations” and was further
updated in 1969 under the name of “International Health
Regulations”
• They were originally aimed at controlling six diseases: cholera,
plague, yellow fever, smallpox, relapsing fever and typhus.
• Different factors might affect the completeness and accuracy of
records of communicable diseases. Most of them are the same
issues affecting mortality reports too. An specific factor for
incompleteness of infectious diseases: they person affected
needs to go/taken to a health facility
MORBIDITY DATA. NCDs
• Probably the best established reporting system outside
communicable diseases are the cancer registers.
• Cancer registers allow the monitoring of trends of
incidence, prevalence and survival rates of all cancers and
also collect information on exposures that serves the
basis for epidemiological research
• The UK National Cancer Intelligence Network [NCIN] part
of PHE receives regional data and produces secondary
analysis and research.
• Other NCDs with good established registers are diabetes
and heart diseases among others.
• Surveillance systems for chronic diseases are also used
to organise recall of patients for check ups and
medication review.
MORBIDITY DATA.CONGENITAL
DISEASES.
• Following the tragedy of thalodomine
[prescribed to pregnant women in the 60s to
prevent morning sickness] and found to
cause limb malformations it was clear the
need to monitor congenital diseases.
• The thalodomine tragedy triggered the
creation in UK of the National Congenital
Anomaly System [NCAS] in 1964.
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Health centres and hospital data
• Information collected by health centres and hospitals is
very wide in type and serves different purposes.
Generic data collected in health centres and hospitals…
• Patient’s contacts,
• Hospital stay [length]
• Interventions implemented [e.g.: surgical interventions]
• Patients outcome
• Patients perceptions
And so on…
Health centres and hospital data [II]
Sources of incompleteness and lack of accuracy in data
expected from health providers:
- Human error
- Private sector and especially “complementary” medicine
centres not always obliged to report
- No everybody access health care when is needed [e.g.:
gender bias]
- Access to health care depends on “severity”
RECOMMENDED READING
• WHO and CDC [2010] “Integrated disease surveillance and
response in the African region”
• Bray F et al (2014) Planning and Developing PopulationBased Cancer Registration in Low- and Middle-Income
Settings. WHO/IARC.
• WHO Immunization
surveillance,
assessment and
monitoring.
TO
LEARN
MORE…
http://www.who.int/immunization_monitoring/routine/surveilla
nce_publication/en/index.html
Data, statistics and graphics:
http://www.who.int/immunization_monitoring/data/en/