PTS-RST-PKH- 2- 2014 1

KONSEP DASAR EPIDEMIOLOGI2/2014

DISIAPKAN OLEH PROF. DR.DRH.PRATIWI, TS. MS

DRH.ROSITAWATI, I. MP

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Disease is the result of forces within a dynamic system consisting of:agent of infection

hostenvironment

Epidemiologic Triad

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Infectious disease

Terminology untuk menggambarkan penyakit infeksi berkaitan dengan keadaan dan prevalensi penyakit pada populasi meliputi◦ Infectivity◦Pathogenicity◦Virulence

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Agent

Host

Environment

• Age• Sex• Genotype• Behaviour• Nutritional status• Health status

• Infectivity• Pathogenicity• Virulence• Immunogenicity• Antigenic stability• Survival

• Weather• Housing• Geography• Occupational setting• Air quality• Food

(www)

Factors Influencing Disease Transmission

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Infectivity

the percentage (or proportion) of individuals exposed to a particular agent who become infected

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No of infected following exposure

Total of population at exposure

Infectivity =

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Pathogenicity

the percentage of infected individuals who develop clinical disease due to the particular agent

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No of clinically affected following exposure

Total of infected at exposure

Pathogenicity =

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Virulence

the percentage of individuals with clinical disease who become serious ill or die

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No of severe (fatal) cases following exposure

Total of clinically infected cases at exposure

Virulence =

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AgentsBiological

◦Viruses Bacteria Parasites or prionsChemical

◦Toxins◦Man-made (Dioxins and melamine)◦Inorganic/organic: zearalenone

Physical◦Foreign bodies◦Trauma◦Radiation

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Agent Factors Host

DoseEnvironmental

hardinessVirulence

(microbial)Infectivity

(microbial)Toxicity (poisons)

Natural host: ◦agent has adapted

itself and co-exists in balance in the host

Atypical host: ◦agent is not normally

encountered

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Host Host Demography

◦ Age, Sex, Species, Breed◦ Production type / level,

Density

Biology◦ Genetics, behavior

Management◦ Intensive (housing) /

extensive (free roaming)◦ Nutrition◦ Hygiene◦ Husbandry◦ Vaccination / medication

Herd immunity◦ Innate (genetic capability)◦Acquired through

vaccination or deliberate exposure

◦Proportion of total population that is resistant to a disease agent

Susceptibility◦Lack of resistance to the

disease agent

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Host Factors

Innate resistance (e.g. gastric barrier, mucocilliary transport mechanism)

Previous exposurePassive immune

status (neonates)Vaccination status and

responseAgeGender

Behavior (e.g. mutual grooming, dominance, pica)

Production status (e.g., lactating vs. non-lactating)

Reproductive status (e.g., pregnant vs. non-pregnant, sterile vs. intact)

Genetics

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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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Ecological Factors in Infections

Altered environment{Air conditioning}

Changes in food production & handling{intensive husbandry with antibiotic protection; deep-freeze; fast

food industry}

Climate changes{Global warming}

Deforestation

Ownership of (exotic) pets

Air travel & Exotic journeys / Global movements

Increased use of immunosuppressives/ antibiotics

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Dua (2) Jenis studi epidemiologi

Menelaah distribusi suatu penyakit pada suatu populasi & mengamati gambaran mendasar sebarannya menurut waktu – tempat – individu terserang

Desain studi:◦Sigi kesehatan ‘masyarakat’ (≈

studi cross sectional, studi deskriptif

Menguji hipotesis tentang hubungan antara kejadian penyakit dengan kemungkinan penyebabnya, melalui pelaksanaan studi epidemiologi yang menghubungkan exposure dengan penyakit yang diduga

Desain studi:◦ Cohort, case-control

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Deskriptif Analitik

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•Nutrients•Poisons•Allergens•Radiation•Physical trauma

Agen

•Kepadatan•Atmosfir•Modus komunikasi (vector, vehicle, reservoir)

Faktor Lingkungan

•Genetic endowment•Immunologic state•Age•Personal behaviour

Faktor Inang

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KONSEP EPID DALAM POPULASI

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TRIAD dasar epidemiologi deskriptif2/22/2014

Waktu

TempatIndividu

Tiga karakteristik esensial kejadian suatu penyakit yang berusaha dielusidasi dalam epidemiologi

deskriptif

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•Berubah atau stabil? topografi•Variasi musiman•Clustered (epidemic) or evenly (endemic) distributed•Point source or propagated

Waktu

•Secara geografis terbatas atau tersebar (pandemi)•Berhubungan dengan suplai air/pakan?•Multiple cluster or one?

Tempat

•Spesies•Bangsa/Ras•Umur•Kelamin

Individu

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TRIAD dasar epidemiologi analitik2/22/2014

Inang

LingkunganAgen

Tiga phenomena yang dikaji dalam epidemiologi analitik

Catatan: ingat terminologi necessary – sufficient - contributory

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•Nutrients•Poisons•Allergens•Radiation•Physical trauma

Agen

•Kepadatan•Atmosfir•Modus komunikasi (vector, vehicle, reservoir)

Faktor Lingkungan

•Genetic endowment•Immunologic state•Age•Personal behaviour

Faktor Inang

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Penularan Penyakit Vertikal horizontal langsung tidak langsung media penularan vektor

mekanik daur hidup

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Definitions Infectious diseases

Caused by an infectious agent Communicable diseases

Transmission – directly or indirectly – from an infected person Transmissible diseases

Transmission – through unnatural routes – from an infected person

Note Infections are often subclinical – infections vs infectious diseases! Antonyms not well-defined

Non-communicable diseases – virus involved in pathogenesis of diabetes?Chronic diseases – HIV?

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Tetanus Measles vCJD

(www)

Infectious Disease

Cases Index – the first case identified Primary – the case that brings the infection into a population Secondary – infected by a primary case Tertiary – infected by a secondary case

P

S

S

T

Susceptible

Immune

Sub-clinical

Clinical

ST

(www)

Transmission

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Chain of transmission

Direct

Direct contact

Secretions, Blood, Faeces/urine

Droplet spread

Indirect

Food/water

Aerosol

Animal vectors

Fomites

Medical devices and treatments

Mode of Transmission

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Chain of transmissionReservoir

Human

Person with symptomatic illness

Carriers:

Asymptomatic

Incubating

Convalescent

Chronic

Animal: zoonosis

Environmental: soil, plant, water

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Chain of transmission

Human/animal

Respiratory tract

Genito-Urinary tract

Faeces

Saliva

Skin (exanthema, cuts, needles, blood-sucking arthropods)

Conjunctival secretions

Placenta

Environmental

Cooling towers

Portal of exit

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Respiratory tract

Mouth (faecal-oral transmission)

Skin

Mucous membranes

Blood

Portal of entry

Chain of transmission

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Chain of transmission

Indirect

Food/water

Aerosol

Animal vectors

Fomites

Medical devices and treatments

Mode of Transmission

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Chain of transmission

Direct

Direct contact

Secretions, Blood, Faeces/urine

Droplet spread

Mode of Transmission

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Chain of Transmission

Portal of exit

Portal of entry

Agent

Susceptible Host

Mode of transmission

ReservoirPerson to person transmission

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Chain of transmission

Human/animal

Respiratory tract

Genito-Urinary tract

Faeces

Saliva

Skin (exanthema, cuts, needles, blood-sucking arthropods)

Conjunctival secretions

Placenta

Environmental

Cooling towers

Portal of exit

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Routes of transmission

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Direct Skin-skin

Herpes 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

(www)

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