Transcript Steps in retrospective epidemiological analysis (REA)

Epidemiologic
method of
investigation
Purpose of epidemiology analysis
is a study of character, level and
dynamics of epidemic process,
what is going in a certain
territory (settlement, district,
region, edge, republic) in the
certain span of time (month,
quarter, half-year, year, a few
years )
Conducting an epidemiological analysis,
an epidemiologist sets before itself the
followings problems:
1) To expose conformities to the law of
epidemic process and his feature at
certain infectious diseases in concrete
terms;
2) It is correct to define these
conformities to the law, unseal their
reasons;
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3) It study efficiency conducted in the
previous year (or years) of and
prophylactic measures;
4) To work out a plan of measures,
directed on a decline or liquidation of
separate infectious diseases, taking
into account the features of epidemic
process of one or another disease in
the concrete terms of the proper area.
Materials, necessary for an epidemiology analysis. For an
epidemiology analysis the followings materials are needed:
1) description of district, cities, regions on the whole; state of dwelling
fund, sewage system and cleaning of territory; presence of different
objects, factories, factories, artels, food enterprises, markets,
stations etc
2) demographic information for a few years about number and age
composition of population, birth-rate, death rate, migration;
3) information about the social and professional structure of population;
4) Number and sanitary state of schools of nurseries, managers and
scope by them to child's population;
5) sanitary state of schools, their number and quantity of schoolboys;
6) state of medical service: and) material well-being by doctors and
middle medical personnel;
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7) information of individual registration of contagious diseases, cards
of urgent notification and epidemiology inspection (forms 58 and
171);
8) magazines of registration of infectious diseases
9) forms 85-87 and sanitary epidemiological centre and form;
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10) information about a death rate and lethality;
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11) information of laboratory researches of material from sick and
healthy persons, inspected on the testimonies of epidemiology or
according to plan;
12) at the analysis of morbidity zoonological information (quantity
and morbidity of rodents, morbidity of wild and home animals by
hydrophobia, brucellosis in the whole region , districts and on the
inhabited areas
13) at the analysis of morbidity bloody and intestinal infections there
is entomological information (quantity of mosquitoes, flies, their
infection).
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Except for the indicated materials
needed:
1) reviews of epidemiological and
statistical forms of account of
infectious morbidity for a previous
year.
2) plan of antiepidemiological work for
current period.
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An epidemiological analysis consists of
a few sections. It begins from the
detailed description of natural and
economic features of territory.
Geographical position, climatic terms,
fauna, flora, soil, reservoirs of
settlement, industrial objects, cultural
welfare and demographic data are
cited, is described in this part.
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Dynamics of morbidity on years. It is
necessary to analyse morbidity for a
few years, because here direction of
epidemic process comes to light more
exactly. For the analysis of infectious
morbidity in years it is necessary to
use intensive indexes. Studying the
level of epidemic process in a
dynamics of years, it is necessary to
make an effort to find out reasons of
its increase or decline for studied
period.
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Study of distributing of infectious
diseases on territory. To select the
most staggered areas of city,
settlements,burrows etc and to
analyse character of morbidity in
them. It is necessary to select
settlements (districts) with more high
and more low morbidity, explaining
reasons of its different level.
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Analysis of monthly morbidity. At the
analysis of morbidity a large value has
a study of reasons of advancing
morbidity in the certain months of
year (seasonality). It is known that
seasonality of infections can depend
on climatic terms (tick encephalitis,
malaria, fever of dengue when the
value of reservoir of virus and carry of
infection rises in distribution of
diseases, and from production and
economic activity of man (rabbit-fever,
brucellosis).
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The degree of contagiousity can
influence one or another infection and
change of intercourse of people
different periods of year (scarletfever,
measles and other). At the row of
communicable diseases seasonality
can change depending on the terms of
life of people and equipping with
modern amenities of the inhabited
places.
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Seasonality of infections can be
studied on the basis of absolute
numbers of morbidity on the months
of year (information of forms 85-87
and cards of epidemiology inspection
of one or another infection). Carefully
analyzing these materials, it is possible
to exclude from the seasonal spread of
diseases, related to the flashes or
infection as a result of the use of the
infected food product or water, and
also cases diseases, related to the
infection in other settlements.
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Analysis of age morbidity. Analysing
morbidity, an epidemiologist must
define how the persons of different
ages are often ill. The study of this
question allows correctly to organize a
fight on the decline of morbidity
among the separate groups of ages
from intensity of their defeat. We will
suppose, analysing morbidity
diphtheria, it is set that children are
most often ill from this infection in age
8—9 years.
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Morbidity on the groups of ages is
studied usually in indexes on 10000
(or on 1000) population of the proper
age. The absolute numbers of
morbidity are not recommended for
such analysis, similarly as extensive
indexes. The analysis of age morbidity
in extensive indexes allows to judge
only about average of separate age
group in annual morbidity on a
settlement on the whole, but he can
not show frequency of diseases on the
different groups of ages.
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Analysis of morbidity on the
professionally-domestic groups of
population. The studying of morbidity
on professionally-domestic groups
allows an epidemiologist to expose
most staggered one or another
infection of group of population and at
planning and conducting of
prophylactic and antiepidemiological
measures for the decline of morbidity
to pay the special attention to work
among the most staggered
contingents.
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At the analysis of distributing of
morbidity different infections on the
professionally-domestic groups of
epidemiologist can interest the
different groups of population. So,
analyzing morbidity brucellosis, it is
necessary to find out, what groups of
rural or urban population are most
staggered this infection (milkmaids,
persons who tends cattle, shepherds,
workers of creameries, meat-packing
plants ).
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Analysis of sources and ways of
passing to the infection. An exposure
of sources is infections which resulted
in appearance of new case of disease,
and also determination of ways of
transmission, instrumental in
distribution of the contagious
beginning, is an important section in
work of epidemiologist.
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Study of efficiency of measures in
regard to the source of infection
(exposure, timeliness of diagnostics
and quality of hospitalization). The
timely conducting of
antiepidemiological measures in an
infectious place (early exposure, timely
diagnostics and hospitalization).
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Studying of efficiency of measures in
the focus of infectious disease. After
an exposure and hospitalization of
infectious patient at the row of
diseases final disinfection is
conducted, that must result in
liquidation of possibility of distribution
of the contagious beginning through
the articles of everyday life (at
intestinal infections, infections of
outward covers, tuberculosis).
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Estimation of efficiency of bacterial
profile. At the row of infectious
diseases (diphtheria, poliomyelitis) the
most effective mean of fight is vaccine
prophylaxis. To judge about efficiency
of this morbidity among correctly
instiled, noninoculated and inoculated
wrong. For the example of such
analysis it is suggested to study
efficiency tips at diphtheria.
SCHEME OF RELATIONSHIP BETWEEN EPIDEMIOLOGY AND RELATED DISCIPLINES
Microbiology, Virology,
Parasitology, Clinic of
infectious diseases,
Epizootiology,
Noninfectious clinical
disciplines,
Occupational pathology,
Pathological anatomy
Health statistics,
Hygiene, Health
organization
EPIDEMIOLOGY
Evolutionary theory,
Ecology, General and
molecular biology,
Genetics, Medical and
Biological Chemisty,
Immunology,
Geography,
Anthropology
History,
Economics,
Social Hygiene,
Archeology
Comprehensive study of epidemiological methods
Descriptive-histological
and
comparative-histological (can reveal
patterns of evolution of disease,
predict their distribution in the
future)
Ecological
method
(reservoir
pathogen carriers and other natural
structure of cells, ranges)
The method of statistical analysis
(quantitative study level, dynamics,
focus of disease, seasonal patterns and
other diseases)
Molecular
biological
method
(mechanism and causes of variability of
influenza
virus
toxigenicity
corynebacterium, microbial resistance
to drugs etc)
Geographical and mapping method
(addiction epidemics of natural
factors: natural focus, detecting
transmission etc)
Socio-economic
and
socio-hygienic
methods (economic cost of morbidity,
cost-effectiveness
of
preventive
measures, the importance of sociohygienic conditions etc)
Epidemiological survey (clarification
in place of the casual relationships
that drive the epidemic process)
Experimental and epidemiological
method (biology blood-sucking vectors,
the efficiency of insecticide disinfection,
stoked method, etc)
Laboratory and epidemiological methods
(microbiological, serological studies to
identify carriers, patients in cell efficiency
of immunization, disinfection, detecting
contaminated food, water etc)
Sections of Epidemiology
FIELD
What
(instances)
Where (place),
With whom
(person),
When it
happened
(time)
EXPOSITORY
•Who (person)
•Where (place)
•When it
happened (time)
ENTRY
EPIDEMIO
LOGY
ANALYTICAL
How
Why,
Evidencebased
medicine
Sections of Epidemiology
Animals
Wild
Domestic
Synanthropic
Source
Man
Carriers
Acute
form
Sick
Chronic
form
MECHANISM OF
TRANSMISSION
Convalescents
Typical
form
Atypical
form
SUSCEP
TIBLE
ORGAN
ISM
Scheme of infections transmission:
I – Source of infection, II – mechanism of transmission, III
– susceptible organism; 1 – discharging of agent from the
source, 2 – staying in environment, 3 – penetration to
healthy organism.
Structure of parasitic
system in anthroponosis
Biological agents
Structure of parasitic
system in zoonosis
Structure of parasitic
system in sapronosis
Morbidity (Absolute data) ARVI
and influenza in Ternopil Region
and Ternopil city (21.108.11.09)
5000
4000
3000
2000
1000
10
/2
1/2
00
10
9
/2
3/2
00
10
9
/2
5/2
00
10
9
/2
7/2
00
10
9
/2
9/2
00
10
9
/3
1/2
11 009
/2
/20
09
11
/4
/20
09
11
/6
/20
09
11
/8
/20
09
0
Region
City
Morbidity of ARVI and influenza
In Ternopil weekly(2005-2009),
for 10000 population
400
350
300
250
200
150
100
50
2005
2006
2007
2008
2009
51
49
47
45
43
41
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
1
0
City, children
City, adults
11/9/2009
11/8/2009
11/7/2009
11/6/2009
11/5/2009
11/4/2009
11/3/2009
11/2/2009
11/1/2009
10/31/2009
10/30/2009
140
120
100
80
60
40
20
0
10/29/2009
Morbidity of ARVI and influenza among children
and adults in Ternopil region and City (29.109.11.09),
Per 10000 population
Etiological structure of ARVI and Influenza
2009 (in epidemic situation)
Influenza B
Parainfluenza
RS
Adenovirus
грип А
influenza B
Parainfluenza
RS
Adenovirus
2008
OBJECTIVE RETROSPECTIVE EPIDEMIOLOGICAL ANALYSIS
1
2
Estimated epidemical situation
based on:
Determining patterns of the
epidemic process
Studying the structure
of infectious diseases
Social
meaning
Character of
changes in time
Character of
changes in
territory
Economical
meaning
6
7
Predicting infectious morbidity
situation for the next year
Studying characteristics of the
epidemic, the most topical
infections and their causes in
specific contexts
Trends
Detection of infectious
diseases which are
most common
Epidemical
meaning
3
Developing rational and
scientifically sound approach to
planning preventive and antiepidemic measures in the
specific area
4
Identifying natural and social
conditions
and
precursors
complications of epidemical
situation in a particular area
5
Evaluating the effectiveness of
prophylactic and preventive
measures undertaken in the
previous period
Steps of retrospective epidemiological
analysis
І step
Assembly of program of
investigation
Definition of objectives
REA
Identification of major
Directions REA
ІІ Step
Collection and preprocessing informatio
Demographic data
Sanitary-hygienic characteristic of district
Natural, social and working conditions of populat
Steps in retrospective
epidemiological analysis (REA)
I step 1
Composing software survey
Визначення
завдань
Definition
of objectives
(REA)
РЕА
II step 2
Collecting and preprocessing
information about:
Infectious morbidity
step 3
Studying of information about infectious morbidity
Analysis of level and structure of infectious morbidity
Analysis of long-term dynamics of morbidity
trends
Demographic data
Identification of major areas
of REA
III
Sanitary-hygienic
characteristic of district
periodicity
Average analysis
Annual analysis
Level of annual morbidity
Natural, social and working
conditions of population
Terms of seasonal increasing
Duration of seasonal increasing
Analysis of morbidity according to risk factors
IV
Step 4
Copmosition of retrospective epidemical diagnosis
and revealing of actual problems of infectious
morbidity to certain territories
Age characteristic
Professional characteristic
Sex characteristic
Analysis of morbidity according to territory
Seasonal character of Leptospirosis in Ternopil
Region (1981-1999 )
Fecal-oral mechanism
Air-borne mechanism
Transmissive mechanism
Contact (wound) mechanism
Epidemiological methods
For achieving the above objectives various methods
are used by epidemiologists. They have evolved
from 19th century:
1. Observational
2. Experimental
 Observational – as the name implies
involves only making observations on what
has happened to persons and communities
and make inferences from these observations.
It may be further classified into descriptive
and analytical.
Descriptive studies
observe health phenomena in terms of time /
place / person.
- Cross-sectional made on populations or
communities at one point of time. They give
information on the community just as a cross
section of a specimen gives informationat that
particular level of sectioning.
- Longitudinal surveys conducted over long
periods in the same population. They give
information over different time points. Useful in
calculating incidence rates and drawing time
trends in health and disease.
Analytical designs
Based on specific hypothesis generated
from cross sectional or longitudinal
studies. Used to gather data and the
data is analysed to test the specific
hypotesis. May be called retrospective
studies when both the exposure and
outcome has occurred before the
study commences. They are
prospective when both exposure and
outcomes are yet to occur.
Experimental design
Are methods where suspected causal situation
is induced in selected and control populations
and their effects are observed to prove or
disprove a hypothesis. The major modalities
of experimental designs in vogue currently
may be classified as follows:
- Randomised controlled clinical trial;
- Field trials;
- Community trials.
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Inspection – revealing of the source
Examination – studying of morbidity
Analysis of morbidity
Experiment – microbiological and
serological examination, physical and
chemical studies, experiment on
humans and animals
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