Principles of Principles of Disease and Disease and

EpidemiologyEpidemiologyHow do we know you are sick How do we know you are sick let alone that its an epidemic?let alone that its an epidemic?

Defining Some TermsDefining Some Terms

PathologyPathology Study of diseaseStudy of disease EtiologyEtiology Study of the cause of a Study of the cause of a

diseasedisease PathogenesisPathogenesis Development of diseaseDevelopment of disease InfectionInfection Colonization of the body Colonization of the body

by pathogensby pathogens DiseaseDisease An abnormal state in which An abnormal state in which

the the body is not functionally body is not functionally normallynormally

• Symbiosis is the relationship Symbiosis is the relationship between organisms living togetherbetween organisms living together• Commensalism Commensalism

• one organism is benefited one organism is benefited • the other is unaffected.the other is unaffected.

• MutualismMutualism• both organisms benefit.both organisms benefit.

• ParasitismParasitism• one organism is benefited at the expense of one organism is benefited at the expense of

the other.the other.

SymbiosisSymbiosis

Transient microbiota may be present Transient microbiota may be present for days, weeks, or monthsfor days, weeks, or months

Normal microbiota permanently Normal microbiota permanently colonize the hostcolonize the host

Some normal microbiota are Some normal microbiota are opportunistic pathogens.opportunistic pathogens.

You as EcosystemYou as Ecosystem

Figure 14.2

• Locations of Locations of normal normal microbiota on microbiota on and in the and in the human bodyhuman body

Normal Microbiota and Normal Microbiota and the the

Host: Host:

Normal microbiota protect the host by: Normal microbiota protect the host by: occupying niches that pathogens might occupying niches that pathogens might

occupyoccupy producing acidsproducing acids producing bacteriocinsproducing bacteriocins

Probiotics are live microbes applied to Probiotics are live microbes applied to or ingested into the body, intended to or ingested into the body, intended to exert a beneficial effect.exert a beneficial effect.

Normal Microbiota and Normal Microbiota and the Host:the Host:

Some Normal FloraSome Normal Flora

Koch's Koch's Postulates Postulates are used to are used to prove the prove the cause of an cause of an infectious infectious disease.disease.

Koch’s PostulatesKoch’s Postulates

Figure 14.3.1

Koch's Koch's Postulates Postulates are used to are used to prove the prove the cause of an cause of an infectious infectious disease.disease.

Koch’s PostulatesKoch’s Postulates

Figure 14.3.2

Classifying Infectious Classifying Infectious DiseasesDiseases

SymptomSymptom A change in body function A change in body function that is felt by that is felt by a patient as a a patient as a result of result of diiseasediisease

SignSign A change in a body that A change in a body that can be can be measured or observed as a measured or observed as a

result result of disease.of disease. SyndromeSyndromeA specific group of signs and A specific group of signs and

symptoms that accompany a symptoms that accompany a disease.disease.

Classifying Infectious Classifying Infectious DiseasesDiseases

Communicable diseaseCommunicable disease spread from one spread from one host to host to another.another.

Contagious diseaseContagious disease easily spread from easily spread from one one host to another.host to another.

Noncommunicable diseaseNoncommunicable disease not transmitted not transmitted from one host from one host

to to another.another.

IncidenceIncidence Fraction of a population that Fraction of a population that contracts a disease during a contracts a disease during a specific time.specific time.

PrevalencePrevalence Fraction of a population having Fraction of a population having a specific disease at a a specific disease at a

given time.given time. Sporadic diseaseSporadic disease Disease that occurs Disease that occurs

occasionally in a population.occasionally in a population. Endemic diseaseEndemic disease Disease constantly present in a Disease constantly present in a

population.population. Epidemic diseaseEpidemic disease Disease acquired by many Disease acquired by many

hosts in a given area in a hosts in a given area in a short short time.time.

Pandemic diseasePandemic disease Worldwide epidemic.Worldwide epidemic.

Occurrence of DiseaseOccurrence of Disease

Acute diseaseAcute disease Symptoms develop Symptoms develop rapidlyrapidly

Chronic diseaseChronic disease Disease develops Disease develops slowlyslowly

Subacute diseaseSubacute disease Symptoms between Symptoms between acute and acute and

chronicchronic Latent diseaseLatent disease Disease with a period of Disease with a period of

no symptoms when the no symptoms when the patient is infectivepatient is infective

Severity or Duration of Severity or Duration of a Diseasea Disease

The Stages of a DiseaseThe Stages of a Disease

Figure 14.5

Reservoirs of infection are continual Reservoirs of infection are continual sources of infection.sources of infection. Human — AIDS, gonorrheaHuman — AIDS, gonorrhea

Carriers may have inapparent infections or latent Carriers may have inapparent infections or latent diseasesdiseases

Animal — Rabies, Lyme diseaseAnimal — Rabies, Lyme disease Some zoonoses may be transmitted to humansSome zoonoses may be transmitted to humans

Nonliving — Botulism, tetanusNonliving — Botulism, tetanus SoilSoil

Reservoirs of InfectionReservoirs of Infection

Reservoirs of infection are continual Reservoirs of infection are continual sources of infection.sources of infection. Human — AIDS, gonorrheaHuman — AIDS, gonorrhea

Carriers may have inapparent infections or latent Carriers may have inapparent infections or latent diseasesdiseases

Animal — Rabies, Lyme diseaseAnimal — Rabies, Lyme disease Some zoonoses may be transmitted to humansSome zoonoses may be transmitted to humans

Nonliving — Botulism, tetanusNonliving — Botulism, tetanus SoilSoil

Reservoirs of InfectionReservoirs of Infection

ContactContact DirectDirect Requires close association Requires close association

between between infected and infected and susceptible hostsusceptible host

IndirectIndirect Spread by fomitesSpread by fomites DropletDroplet Transmission via airborne Transmission via airborne

dropletsdroplets

Transmission of DiseaseTransmission of Disease

Transmission of DiseaseTransmission of Disease

Figure 14.6a & 8

VehicleVehicle Transmission by an inanimate Transmission by an inanimate reservoir (food, water) reservoir (food, water)

VectorsVectors Arthropods, especially fleas, ticks, Arthropods, especially fleas, ticks, and mosquitoesand mosquitoes

MechanicalMechanical Arthropod carries pathogen on Arthropod carries pathogen on feetfeet

BiologicalBiological Pathogen reproduces in Pathogen reproduces in vectorvector

Transmission of DiseaseTransmission of Disease

Transmission of DiseaseTransmission of Disease

Figure 14.6b, c

Figure 14.7, 9

Are acquired as a result of a hospital stayAre acquired as a result of a hospital stay 5-15% of all hospital patients acquire 5-15% of all hospital patients acquire

nosocomial infectionsnosocomial infections

Nosocomial (Hospital-Nosocomial (Hospital-Acquired) InfectionsAcquired) Infections

Figure 14.10

Relative frequency of Relative frequency of nosocomial infectionsnosocomial infections

Common Causes of Common Causes of Nosocomial InfectionsNosocomial Infections

Percentage of Percentage of nosocomial nosocomial infectionsinfections

Percentage Percentage resistant to resistant to antibioticsantibiotics

Gram + cocciGram + cocci 34%34% 28%-87%28%-87%

Gram – rodsGram – rods 32%32% 3-34%3-34%

Clostridium Clostridium difficiledifficile

17%17%

FungiFungi 10%10%

Diseases that are new, increasing in Diseases that are new, increasing in incidence, or showing a potential to increase incidence, or showing a potential to increase in the near future.in the near future.

Contributing factors:Contributing factors: Evolution of new strainsEvolution of new strains

V. choleraeV. cholerae O139 O139 Inappropriate use of antibiotics and Inappropriate use of antibiotics and

pesticidespesticides Antibiotic resistant strainsAntibiotic resistant strains

Changes in weather patternsChanges in weather patterns HantavirusHantavirus

Emerging Infectious Emerging Infectious DiseasesDiseases

Contributing factors:Contributing factors: Modern transportationModern transportation

West Nile virusWest Nile virus Ecological disaster, war, expanding human Ecological disaster, war, expanding human

settlementsettlement CoccidioidomycosisCoccidioidomycosis

Animal control measuresAnimal control measures Lyme diseaseLyme disease

Public Health failurePublic Health failure DiphtheriaDiphtheria

Emerging Infectious Emerging Infectious DiseasesDiseases

The study of The study of where and where and when diseases when diseases occuroccur

EpidemiologyEpidemiology

Figure 14.11

Principles of Disease Principles of Disease SurveillanceSurveillance

www.who.int/emc/slideshows/Survintro/sld001.htwww.who.int/emc/slideshows/Survintro/sld001.htmm

EpidemiologyEpidemiology

John SnowJohn Snow 1848-18491848-1849 Mapped the Mapped the occurrence of cholera occurrence of cholera in Londonin London

Ignaz Ignaz SemmelweisSemmelweis

1846-18481846-1848 Showed the hand Showed the hand washing decreased washing decreased the incidence of the incidence of puerperal feverpuerperal fever

Florence Florence NightingaleNightingale

18581858 Showed that improved Showed that improved sanitation decreased sanitation decreased the incidence of the incidence of epidemic typhusepidemic typhus

• • DescriptiveDescriptive Collection and analysis of Collection and analysis of data regarding data regarding occurrence of diseaseoccurrence of disease

SnowSnow

• • AnalyticalAnalytical Comparison of a diseased Comparison of a diseased group and a healthy group and a healthy groupgroup

NightingaleNightingale

• • ExperimentalExperimental Study of a disease using Study of a disease using controlled experimentscontrolled experiments

SemmelweisSemmelweis

• • Case reportingCase reporting Health care workers Health care workers report specified disease report specified disease to local, state, and to local, state, and national officesnational offices

• • Nationally Nationally Notifiable Notifiable DiseasesDiseases

Physicians are required to Physicians are required to report occurrencereport occurrence

MethodsMethods

Table 14.7

Collects and analyzes epidemiological Collects and analyzes epidemiological information in the U.S. information in the U.S.

Publishes Morbidity and Mortality Weekly Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.govReport (MMWR) www.cdc.gov

Morbidity: incidence of a specific notifiable Morbidity: incidence of a specific notifiable diseasedisease

Mortality: deaths from notifiable diseasesMortality: deaths from notifiable diseases

Morbidity rate = number of people Morbidity rate = number of people affected/total population in a given time affected/total population in a given time periodperiod

Mortality rate - number of deaths from a Mortality rate - number of deaths from a disease/total population in a given timedisease/total population in a given time

Centers for Disease Control Centers for Disease Control

and Prevention (CDC)and Prevention (CDC)

CDC and MMWRCDC and MMWR

Centers for Disease Control and PrevCenters for Disease Control and Preventionention

Morbidity and Mortality Weekly ReporMorbidity and Mortality Weekly Reportt Published by the CDCPublished by the CDC Weekly information on reportable Weekly information on reportable

diseasesdiseases