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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