1
Epidemiology
of infectious diseases
Kolářová M., EPI Autumn 2017
EPIDEMIOLOGY
is the study (scientific, systematic, data-driven)
of the distribution (frequency, pattern)
and determinants (causes, risk factors)
of health-related states or events (not just diseases)
in specified populations (patient is community,
individuals viewed collectively),
and the application (since epidemiology is a discipline
within public health)of this study to the control of health
problems.
2
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Solving
health
problem
Step 1
Date collection
Step 2
Assessment
Step 3
Hypothesis
testing
Step 4
Action
Surveillance;
determine time,
place and person
Inference
Determine how
and why
Intervention
 Sporadic Disease that occurs occasionally in a population.
 Endemic Disease constantly present in a population at
all times – malaria is present in Africa at all time because of the
presence infected mosquitos.
 Epidemic or outbreak Disease occurence among a
population that is in excess of what is expected in a given area
in a short time – the Ebola virus in parts of Africa is in excess of
what is expectes for this region.
 Pandemic Disease or condition that spread across world –
HIV/AIDS is one of the worst global diseases in history.
Occurrence of Disease
 Incidence - measures the number of new cases over time.
This number measures an individual chances of developing or
contracting the disease.
Number of new cases within a specified time period
Total number of people in the population
 Prevalence – measures the total number of cases of disease in
a population.
Total number of diseases individuals
Total number of people in the population at a given time
Disease trends
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Epidemiologic investigations are
largely mathematical
descriptions of persons in groups,
rather than individuals.
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The basic quantitative
measurement in epidemiology is
a count of the number of persons
in the group being studied who
have a particular disease.
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Epidemiologists arrange their data in various ways,
depending on what aspect of the information they want
to emphasize.
One of the most powerful tools an
epidemiologist can use is case reporting:
reporting specific diseases to
* local,
* state and
* national health authorities,
who accumulate the data
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Modern infectious disease
epidemiology
10
Slime-producing coagulase-negative staphylococci. Scanning electron micrograph of the
surface of an intravascular catheter incubated in vitro with (a) slime-producing and (b)
nonslime-producing strains of Staphylococcus epidermidis. With permission from
Christensen.9
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Staphylococcus aureus
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 b-Hemolytic streptococci group A on a blood agar plate.
Note the clear b-hemolytic zone.
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 Electron microscopy of group A streptococcus. The
fuzzy M protein layer can be seen protruding from
the cell wall..
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Mixed culture of two morphotypes of Enterobacteriaceae on
blood agar plate (Escherichia coli and Salmonella spp.).
15
Pseudomonas aeruginosa monotrichous polar flagellum seen
on electron microscopy.
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Obtained after an outbreak, this micrograph depicts Gram-positive
Clostridium difficile bacteria.
Source: CDC
17
Under a moderately-high magnification of 8000X, this colorized scanning
electron micrograph (SEM) revealed the presence of a small grouping of Gramnegative
Salmonella typhimurium bacteria that had been isolated from a pure
culture. See PHIL 10986 for a black and white version of this image.
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Cultured Helicobacter pylori in coccoid and bacilli forms, bound to
immunomagnetic beads.
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Ziehl-Neelsen stain of 'cords' of Mycobacterium tuberculosis
isolated from a broth culture. Tubercle bacilli aggregate end to
end and side to side to form serpentine cords, especially in
broth cultures.
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Helical structure of Treponema pallidum with the periplasmic
flagella.
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Rotavirus
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HEPATITIS A VIRUS
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Colonies of Nocardia asteroides showing smooth chalky-white
appearance.
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Giemsa stain of blood with Borellia burgdorferi.
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Hlístice Trichinella spiralis
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Sarcoptes scabiei
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Colonisation and contamination of humans
by micro-organisms.
Many parts of the body are colonized by normal flora, which
can be the source of endogenous infection. Large
numbers of micro-organisms are found in moist areas of
the skin (e.g. the groin, between the toes), the upper
respiratory tract, the digestive tract (e.g. the mouth, the
nasopharynx), the ileum and large intestine, the anterior
parts of the urethra and the vagina.
Other routes are interhuman transmission of infections and
exposure to exogenous contamination.
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the agent of infection (e.g., particular
bacterium or virus),
Organism characteristic:
infectivity – capacity to multiply in host
pathogenicity – capacity to cause disease in host
virulence - pathogenicity in a specific host
immunogenicity – capacity to induce specific and
lasting immunity in host
antigenic stability – can induce long-life immunity
resistance - in environment
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Organisms vary in their capacity to survive in the
free state and to withstand adverse
environmental conditions, for example:
* heat, cold, dryness.
Sporo-forming organisms, such as tetanus bacilli
which can survive for years in a dormant state,
have a major advantage over an organisms like
the gonococcus which survive for only a very
short time outside the human host.
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Morbilli (Measles). A disseminated erythematous rash can be
seen over the trunk and arms.
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 Impetigo in a child.
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Septic pulmonary emboli. Multiple nodular pulmonary infiltrates secondary to a
dialysis catheter-associated infection. The patient presented with high fevers, cough
and pleuritic chest pain. Staphylococcus aureus was isolated from multiple blood
specimens.
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Erysipelas. Note the sharp demarcation of the
affected skin.
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Scarlatina (scarlet fever)
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 Necrotizing fasciitis caused by group A strepococci.
There is only moderate erythema but at surgery there
was extensive soft tissue damage.
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Varicella (chickenpox)
40
Varicella (chickenpox). Lesions at various stages, including
vesicles, can be seen.
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Typical rash of meningococcal septicemia. Fine erythematous
macules and petechiae are present in some areas.
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Rubella
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Parotitis epidemica ( mumps)
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Scabies
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Crusted or Norwegian scabies in a patient who has AIDS.
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Primoinfection HIV
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Gonococcal urethritis.
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Secondary syphilis with typical skin rash.
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Lyme boreliosis (LB)
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LB - Typical erythema migrans rash.
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Burned leg that has been superinfected with Pseudomonas
aeruginosa.
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Primary cutaneous nocardial infection is characteristically painless, localized and
slowly progressive. (a) There is marked swelling and erythema in this child's finger.
(b) However, because the finger was painless the child was not brought to medical
attention until the infection had progressed to involve the entire finger.
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Francisella tularensis
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Tularemia
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Tularemia
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Pathogenesis of rabies.
The chain of infections (epidemic proces)
57
Infectious diseases result from the interaction of
agent, host, and environment (natural, social factors).
More specifically - spreding of infections occurs when:
the agent leaves its reservoirs or host (source) trough a portal of exit,
is conveyed by some mode of transmissin and
enters trough an appropriate portal of entry to infect a susceptible host.
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1. the presence of source of
infection
is the site or sites in which a disease agent normally lives and
reproduces.
May be classified as:
- human - at the ende incubation period,
if is ill,
reconvalescent,
carriers – healthy,
chronic diseases
- animals - at the ende incubation period,
if is ill,
carriers – healthy,
reconvalescent, chronic
The Stages of a Disease
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Staphylococcal nasal carriage. This patient had a small staphylococcal abscess beneath the
mucosa of the nose, illustrating how Staphylococcus aureus, which colonizes the nares, can
infect skin and submucosa. Intact mucosa is highly resistant to infection; such infections
usually occur as a result of defects in the mucosal membranes or via hair follicles inside the
nose.
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EPIDEMIC PROCESS IN THE HOSPITAL ENVIRONMENT
SOURCES
OF INFECTION
MODE
OF TRANSMISSION
trough
biological material
of patients
or contaminated surfaces
or equipments
SUSCEPTIBLE
HOST
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Biological materials – their infectivity
1. Causative agens in blood, derivates from blood, plasma
VHB, VHC, VHA (short in the blood), HIV, CMV, rarely EBV,
virus of morbilli (viremie), kandidy-kandidémie,
malárie - (plasmodia can survive in fresh plasma 3 – 5oC - 14 days),
Toxoplasma gondii - (can survive in blood - 56 days)
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Biological materials – their infectivity
2. Causative agens in droplets
Adenovirus, coronaviruses, enteroviruses, herpes virus,
myxovirus (influenzae), paramyxovirus, RSV, rhinovirus,
Stafylococcus, Streptococcus spp., Meningococcus spp.,
Haemophilus Influenzae, Neisseria meningitis, Bordetella
pertussis, Bordetella parapertussis, Mycoplasma pneumoniae,
Pneumocystis carinii, Kandidy….
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Biological materials – their infectivity
3. Causative agents in stool
Enteroviry (VHA, poliomyelitis), VHE, coxsackie viry,
Adenoviry,
Enterobactericeae (E.coli, Klebsiella pneumoniae,
Pseudomonas aeruginosa, Proteus spp., Citrobacter,
Enterobacter, Serratia apod)
Listeria monocytogenes, Clostridium perfringens, Clostridium
tetani, Pneumocystis carinii
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Biological materials – their infectivity
4. Causative agens in URINE :
Virus of measles, parotitis, CMV, VHB, papovavirus, Listeria
monocytogenes, Candidae
5. LIQUOR
HIV, different causative agents of meningitid
6. Salive
VHB, HIV, CMV, EBV, herpes virus hominis typ 1,2, virus
of measles, rubellla
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Biological materials – their infectivity
7. TEARS, EYE - SECRET
VHB, HIV, adenoviruses, Enterovirus typ 70, Coxsackie A 24,
Staphylococcus aureus, hemophfilus, pneumokoky, moraxely,
chlamydie
8. VAGINA AND CERVIX - SECRET
HIV, VHB, rare VHC, herpes virus hominis typ 1,2,
Streptococcus agalactiae, Neisseria gonorrhoea, Haemophilus
Ducreyi, Treponema pallidum, Trichomonas vaginalis,
Chlamydia lymfogranulomatosis, Chlamydia trachomatis
9. EJACULAT
VHB, HIV, rare VHC, CMV,
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2. the metod of transmission
A/ direct contact
touching, kissing or sexual intercourse (Staphylococcus spp.,
Gonococcus spp.,HIV …),
- vertical transmission – from mother to fetus (VHB, VHC, HIV,
listeria, rubella, cytomegalovirus…)
B/ indirect contact
- inhalation of droplets containing the infectious agents (TBC,
measles, influenza…)
- ingestion of food or water that is contaminated (salmonella,
giardia, Norwalk virus, VHA….)
- biological transmission by insects (malaria, borellia….)
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Routes of transmission
 Air
 Food, Drink or Water
 Direct or indirect contact
* Transplacental
 Insects (Artropods)
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Tick - Ixodes ricinus
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A blood-engorged female Aedes albopictus mosquito feeding on a
human host.
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Among the important environmental factors that affect
an epidemic of infectious diseases are:
poverty, overcrowding, lack of sanitation,
and such uncontrollable factors:
as the season and climate.
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3. the susceptibility of the population or its individual
member to the organism concerned, and the characteristic
of the organism itself.
Host factors :
Non specific immunity
Barrier action (natural barrier)
External barrier:
skin , mucosa
Secretion of skin and mucosa
Accessory organ
Internal barrier: placenta, blood-brain barrier
Phagocytosis
Humoral action :
Complement, Lysozyme, Fibronection, Cytokines.
Specific immunity
Humoral immunity
Immunoglobulin: IgG, IgM, IgE, IgA, IgD
Cell mediated immunity
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Main portals of entry
 Respiratory tract
 Gastro-intestinal tract
 Genito-urinary tract
 Direct break through skin
* surgical and wounds
 Direct into blood via needles/catheters
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THE CAUSATIVE AGENT OF INFECTION (bacteria, viruses, fungi, prions, protozoa)
1. the presence of rezervoir (source) of infection
man, animal at the ende of incubation period
acute stage
cariers
2. the way of transmission A/ direct contact
touching, kissing or sexual intercourse (Staphylococcus spp., Gonococcus spp.,HIV …),
- vertical transmission – from mother to fetus (VHB, VHC, HIV, listeria, rubella, cytomegalovirus…)
B/ indirect contact
- inhalation of droplets containing the infectious agents (TBC, measles, influenza…)
- ingestion of food or water that is contaminated (salmonella, giardia, Norwalk virus, VHA….)
- biological transmission by insects (malaria, borellia….)
3. the susceptibility of the population or its individual members to the organism
concerned Host factors : a g e , n u t r i t i o n, g e n e t i c s
i m m u n i t y – natural (nonspecific),
- acquired
THE INFECTION
= 1. source of infection
……….
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THE CAUSATIVE AGENT OF INFECTION (bacteria, viruses, fungi, prions, protozoa)
1. the presence of rezervoir (source) of infection
man, animal at the ende of incubation period
acute stage
cariers
2. the way of transmission A/ direct contact
touching, kissing or sexual intercourse (Staphylococcus spp., Gonococcus spp.,HIV …),
- vertical transmission – from mother to fetus (VHB, VHC, HIV, listeria, rubella, cytomegalovirus…)
B/ indirect contact
- inhalation of droplets containing the infectious agents (TBC, measles, influenza…)
- ingestion of food or water that is contaminated (salmonella, giardia, Norwalk virus, VHA….)
- biological transmission by insects (malaria, borellia….)
3. the susceptibility of the population or its individual members to the organism
concerned Host factors : a g e , n u t r i t i o n, g e n e t i c s
i m m u n i t y – natural (nonspecific),
- acquired
THE INFECTION
= 1. source of infection
……….
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Prevention of infectious diseases
Isolation of patients:
- Dpt. of infectious diseases,
- „high degree of isolation“ (ebola)
- at home,
- barriers nursing technique
SOURCE
OF INFECTION
MODE
OF TRANSMISSION
SUSCEPTIBLE
ORGANISM
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Prevention of infectious diseases
SOURCE
OF INFECTION
MODE
OF TRANSMISSION
SUSCEPTIBLE
ORGANISM
HANDWASHING, DISINFECTION OF HANDS
LINEN WASHING,
CLEANING
GOOD PREPARING OF FOOD, SAFE
WATER……..,
………
DISINFECTION
STERILIZATION
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Prevention of infectious diseases
SOURCE
OF INFECTION
MODE
OF TRANSMISSION
SUSCEPTIBLE
ORGANISM
i m m u n i t y
– natural (nonspecific),
- acquired (vaccination)
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 The distribution of the
smallpox rash is
usually similar to that
shown here. It is
most dense on the
face, arms and hands,
legs and feet. The
trunk has fewer pocks
than the extremities.
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Smallpox is a disfiguring disease. Three out of ten cases may die. It is caused by variola
virus. The disease is spread by secretions from the patient's mouth and nose, and by material
from pocks or scabs. It is transmitted directly from one person to the next. Close contact with
patients, or their clothing or bedding, is thus required for infection. A patient who has
developed the distinctive symptoms of smallpox will have been exposed to the virus about two
weeks previously.
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If the epidemiology is know, we can
interfere with transmission:
„BREAKING THE CHAIN OF
INFECTION“
Different infections have different
epidemiologies and thus require different
methods of control
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In the practical part it is preoccupied with
preventive measures
repressive measures
related to infectious diseases
Preventive anti-epidemic measures
is a set of measures to prevent the infection
of susceptible individuals:
 primary , when we prevent impact of external
risk factors , or we will increase the resistance
of the individual (epidemiology)
 Secondary prevention is early to find
(diagnosis), treatment and prevention of
further development of the disease and
complications (clinical medicine)
 Tertiary prevention monitors patients who
have overcome the disease
 Include:
Increasing hygienic standards of the population - the most
important is compliance with sanitary regulations relating to water
supply , food , manufacturing and food handling , waste water , waste ,
faeces and so forth.
Vaccination - in order to induce maximum collective immunity.
Evidence and vector control (and the people with them living in the
same household) - on the territory concerned health authorities must
register for (eg. Portability typphoid, salmonella, bacillary dysentery
and diphtheria); must be under constant medical supervision , regular
microbiologically examined or treated . Must submit certain restrictive
measures , always report a change of residence must not endanger
their actions of another person .
Measures to prevent the introduction of infection into collectives entrance
examinations (to work, camp, army, morning filters in
nurseries and kindergartens), prevent the entry into the collective
persons that could be a source of infection (important information too).
Prophylactic desinfection - aims to reduce the number of pathogens
in the external environment (public buildings, medical facilities, public
transport, drinking water, waste water from hospitals, milk
pasteurisation).
Border protection - a system of measures protecting the borders of
the introduction of diseases from foreign persons , materials , goods,
imported animals . It is, among other things. Persons who come from
countries with endemic or epidemic occurrence of serious
communicable diseases . Such passengers must show a valid
vaccination certificate, if you do not or are not vaccinated, subjected to
medical supervision, quarantine or vaccination. Quarantine diseases
as plaque, yellow fever and cholera. As for the people, not absolute
boundaries conserve data. More important is the protection of
imported commodities , which must be accompanied by a certificate
of health or veterinary authorities about their health .
Health education - raising awareness of health and culture of the
inclusion of basic hygiene and epidemiology in school and
extracurricular educational facilities.
Repressive anti-epidemic measures are carried out, if
already established infection
Early and accurate diagnosis of the disease - is a fundamental
prerequisite for initiating rapid and effective punitive measures.
This includes proper epidemiological history , clinical examination and
laboratory tests (microbiological, serological, biochemical etc.).
Reporting sick or suspected of being infected - immediately after
diagnosis or suspected infectious disease patient reports a doctor who
examined him first by sending a relevant form epidemiological department
territorially competent health institute , in the case of highly contagious
diseases or epidemic is reported by telephone directly to the ministry health.
Isolation of the sick - is any department patients and convalescent carriers
so as to prevent transmission of infection to susceptible individuals. The
method determines the physician or epidemiologist .
Epidemiological investigation of the outbreak of the disease - carried out
immediately (preferably in an interview with the patient), defines the scope of
an outbreak of place and time. It is necessary to trace the source of infection
and other potentially infected people; collect basic data about patients and
their contacts and data (age, gender, onset of disease, residence, profession
etc.) to develop epidemic curves and expressing working hypotheses about
the sources and routes of transmission.
It's a set of measures that provide the focus of infection in order to
dispose of it as soon as possible :
active search for infected and suspected infections (possible sources)
quarantine measures for suspected infection in the form of medical
supervision (regular investigation and observation after incubation periods
since the last case of the disease), increased medical supervision (except for
watching a ban on certain risky activities), Quarantine (isolation within the
meaning of the WHO, cholera, plaque, yellow fever)
focal disinfection routine around the patient for elimination EA; final after
transporting or death of the patient,
Active and passive immunization according to the circumstances,
chemoprophylaxis especially antibiotics or antimalarials,
Control of basic hygiene measures , such as drinking water , food ,
removal of garbage , sewage disposal,
health and educational work is the instruction of persons affected and
threatened by means of appropriate behavior.
Monitoring and evaluation of anti-epidemic measures - a day he
performs and evaluates epidemiologist , if necessary, amend or adapt
according to the situation. Efficiency measures are evaluated from a health
and economic perspective.
Measures must be viable , easily workable , understandable and effective
.
The 14 steps of an epidemic investigation
1. Confirm the existence of an epidemic.
2. Verify the diagnosis.
3. Develop a case definition.
4. Develop a case report form.
5. Count the cases (i.e., an approximate analysis).
6. Orient the data (i.e., time, place, and person).
7. Analyze the data (e.g., agent, transmission, and host).
8. Develop a hypothesis.
9. Test the hypothesis.
10.Plan and implement control and prevention measures.
11.Evaluate the implemented measures.
12.Establish or improve the public health surveillance.
13.Write a report.
14.Plan and conduct additional studies.
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