epidemiology of inectious diseases
TRANSCRIPT
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Epidemiology of InfectiousDiseases
Dr.Narumol SawanpanyalertDept. of Medical Services
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Infectious Disease Epidemiology:
Major Differences
A case can also be an exposure
Subclinical infections influence
epidemiology
Contact patterns play major role
Immunity There is sometimes a need for urgency
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What is infectious disease epidemiology?
Epidemiology
Deals with one
population
Risk case
Identifies
causes
Infectious disease
epidemiologyTwo or more populations
A case is a risk factor
The cause often known
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Two or more populationsHumans
Infectious agents
Helminths, bacteria, fungi, protozoa, viruses, prionsVectors
Mosquito (protozoa-malaria), snails (helminths-schistosomiasis)
Blackfly (microfilaria-onchocerciasis)bacteria?
AnimalsDogs and sheep/goatsEchinococcus
Mice and ticksBorrelia
What is infectious disease
epidemiology?
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The cause often known An infectious agent is a necessary cause
What is infectious disease epidemiology then
used for? Identification of causes of new, emerging infections, e.g.
HIV, vCJD, SARS
Surveillence of infectious disease
Identification of source of outbreaks
Studies of routes of transmission and natural history of
infections
Identification of new interventions
What is infectious disease epidemiology?
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Routes of transmission
Direct
Skin-skinHerpes type 1
Mucous-mucous
STI Across placenta
toxoplasmosis
Through breast milk HIV
Sneeze-cough Influenza
Indirect Food-borne
Salmonella
Water-borne Hepatitis A
Vector-borne Malaria
Air-borne Chickenpox
Ting-borne
Scarlatina
Exposure A relevant contact depends on the agent
Skin, sexual intercourse, water contact, etc
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No infection Clinical Sub-clinical Carrier
Death Carrier Immunity No immunity
Outcome
(www)
Exposure to Infectious Agents
http://www.pubhealth.ku.dk/epi_en/Uddannelser/fsv7sem/noter/fsv7s-infdisepi-E05-UK-for_home_page.ppt/http://www.pubhealth.ku.dk/epi_en/Uddannelser/fsv7sem/noter/fsv7s-infdisepi-E05-UK-for_home_page.ppt/ -
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Disease is the result offorces within a
dynamic systemconsisting of:
agent of infection
hostenvironment
Epidemiologic Triad
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Agent
Host
Environment
Age
Sex
Genotype
Behaviour
Nutritional status
Health status
Infectivity
Pathogenicity
Virulence Immunogenicity
Antigenicstability
Survival
Weather
Housing
Geography
Occupationalsetting
Air quality
Food
(www)
Factors Influencing DiseaseTransmission
http://www.epiet.org/course/Presentations/2005/11-%20Infect_Dis_Epidemiology/11-%20Infect_Dis_Epidemiology.ppthttp://www.epiet.org/course/Presentations/2005/11-%20Infect_Dis_Epidemiology/11-%20Infect_Dis_Epidemiology.ppt -
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Infectivity (ability to infect)
(number infected / number susceptible) x 100
Pathogenicity (ability to cause disease)(number with clinical disease / number infected) x 100
Virulence (ability to cause death)
(number of deaths / number with disease) x 100
All are dependent on host factors
Epidemiologic Triad-Related Concepts
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Predisposition to Infections(Host Factors)
Gender
Genetics
Climate and Weather
Nutrition, Stress, Sleep
Smoking
Stomach Acidity
Hygiene
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Bacteria
Viruses
Fungi
Protoctists /Protozoa
Helminths
Infectious Agents
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A host that carries a pathogenwithout injury to itself and
serves as a source of infectionfor other host organisms
(asymptomatic infective carriers)
Reservoirs
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Vectors
A host that carries apathogen without injury to
itself and spreads thepathogen to susceptible
organisms
(asymptomatic carriers ofpathogens)
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Infectious Disease Process
Direct tissue invasion
Toxins
Persistent or latent infection
Altered susceptibility to drugs
Immune suppression
Immune activation (cytokine storm)
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Spreading of Infection
Reservoir of infection provides pathogenwith conditions for survival
Human carriers, asymptomatic or latent
Animal- zoonoses various routes
Nonliving Reservoirs water, fertilizer ect
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Portals of entry and Exit
Pathogens have preferred portals of entryand exit.
Most common portalsRespiratory tract
Gastrointestinal tract
Urogenital tract
Blood to blood
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Nosocomial (Hospital-acquired)
infections 5-15% get infections while in the hospital.
Microbes in hospital
Chain of transmission
Compromised host
Is a hospital the best place to be if you aresick?
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Percentage ofTotal
Infections
PercentageResistant toAntibiotics
Coagulase-
negativestaphylococci
25% 89%
S. aureus 16% 80%
Enterococcus 10% 29%Gram-negativerods
23% 5-32%
C. difficile13% None
Common Causes of NosocomialInfections
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Which Procedure Increases the
Likelihood of Infection Most?
Clinical Focus, p. 422
ANIMATION Nosocomial Infections: Prevention
http://../salaya%2023%20jun%202010/nosocomial_prevention.html -
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Control of Nosocomial
Aseptic techniques
Hand washing (40% compliance)
Infection control staff
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No infection Clinical Sub-clinical Carrier
Death Carrier Immunity No immunity
Outcome
(www)
Exposure to Infectious Agents
http://www.pubhealth.ku.dk/epi_en/Uddannelser/fsv7sem/noter/fsv7s-infdisepi-E05-UK-for_home_page.ppt/http://www.pubhealth.ku.dk/epi_en/Uddannelser/fsv7sem/noter/fsv7s-infdisepi-E05-UK-for_home_page.ppt/ -
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Disease is the result offorces within a
dynamic systemconsisting of:
agent of infection
hostenvironment
Epidemiologic Triad