Download - Principles of Disease and Epidemiology How do we know you are sick let alone that its an epidemic?
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