EpidemiologyEpidemiology

The Study of Disease in PopulationsThe Study of Disease in Populations

EpidemiologyEpidemiology

• TerminologyTerminology• Disease ReservoirsDisease Reservoirs• Acquisition and transmissionAcquisition and transmission• Nosocomial infectionsNosocomial infections• Case study: epidemiology of AIDSCase study: epidemiology of AIDS

Communicable Disease PatternsCommunicable Disease Patterns

Frequency statisticsFrequency statistics

Total number of cases in populationTotal number of cases in population

Total number of ________________ in populationTotal number of ________________ in populationX 100X 100PrevalencePrevalence = =

Number of Number of newnew cases cases

Number of _________________ persons in populationNumber of _________________ persons in population

IncidenceIncidence = =

Example: 100 people, 10 new people with disease --> prevalence of 10/100 = Example: 100 people, 10 new people with disease --> prevalence of 10/100 = 10%10% --> incidence of 10/90 = --> incidence of 10/90 = 1/91/9

10 new people get disease --> prevalence of 20/100 = 10 new people get disease --> prevalence of 20/100 = 20%20%--> incidence of 10/80 = --> incidence of 10/80 = 1/81/8

Morbidity and mortalityMorbidity and mortality

MorbidityMorbidity -- Incidence of a disease in a -- Incidence of a disease in a

population, including both fatal and population, including both fatal and

nonfatal casesnonfatal cases

MortalityMortality -- Incidence of -- Incidence of ________________________________

in a populationin a population

Disease ReservoirsDisease Reservoirs

ReservoirReservoir -- site in which viable infectious -- site in which viable infectious

agents remain _______________ and from agents remain _______________ and from

which infection of individuals may occurwhich infection of individuals may occur Animals (“Animals (“ZoonosisZoonosis” -- a disease which occurs ” -- a disease which occurs

primarily in animals but which can be transmitted to primarily in animals but which can be transmitted to humans): rabies, bovine tuberculosis, malaria, etc.humans): rabies, bovine tuberculosis, malaria, etc.

Human carriersHuman carriers

SourceSource -- actual person or object from which -- actual person or object from which an infection comesan infection comes

Human carriers: individuals who inconspicuously harbor a pathogenHuman carriers: individuals who inconspicuously harbor a pathogen

Asymptomatic carriersAsymptomatic carriers -- infected, but with no -- infected, but with no

________________ manifest________________ manifestCan be because the disease is within an incubation period Can be because the disease is within an incubation period

(“(“acute carriersacute carriers”) or because individuals have either ”) or because individuals have either recovered from an infection or because they have a recovered from an infection or because they have a subclinical infection which has remained non-apparent subclinical infection which has remained non-apparent (“(“chronic carrierschronic carriers””) )

Passive carriersPassive carriers -- not _____________________; -- not _____________________;

infections passed on hands, instruments, etc.infections passed on hands, instruments, etc.

Typhoid Mary: classic asymptomatic chronic carrier

Typhoid Mary: classic asymptomatic chronic carrier

Acquisition and transmissionAcquisition and transmission

Diseases can be Diseases can be communicablecommunicable or or non-non-communicablecommunicable

Epidemiologists search for a Epidemiologists search for a pattern of pattern of

______________________ which may ______________________ which may

indicate the mode of transmissionindicate the mode of transmission

Incidence of viral meningitis in the U.S. Note marked

summer rise and __________________ nature of occurrence

Incidence of viral meningitis in the U.S. Note marked

summer rise and __________________ nature of occurrence

TransmissionTransmission

Direct host-to-host: cold Direct host-to-host: cold & flu, STDs, skin & flu, STDs, skin pathogenspathogens

Indirect host-to-host: Indirect host-to-host: spread via spread via vectorsvectors (living agents) or (living agents) or fomitesfomites (_______________ (_______________ objects)objects)

The shape of an epidemic curve helps to distinguish the likely _____________

The shape of an epidemic curve helps to distinguish the likely _____________

DNA Fingerprinting to Determine Possible Origins of Outbreaks

DNA Fingerprinting to Determine Possible Origins of Outbreaks

New York's Lethal Virus Came From Middle East, DNA New York's Lethal Virus Came From Middle East, DNA SuggestsSuggests

FORT COLLINS, COLORADO--A group of public health researchers FORT COLLINS, COLORADO--A group of public health researchers announced at a workshop held here last week that the DNA sequence of the announced at a workshop held here last week that the DNA sequence of the virus that caused an epidemic of brain inflammation in and around New virus that caused an epidemic of brain inflammation in and around New York City this summer conclusively shows that it is the West Nile virus--an York City this summer conclusively shows that it is the West Nile virus--an identification that was under debate until recently. They also reported that identification that was under debate until recently. They also reported that the virus's genome is almost identical to that of a West Nile strain found in the virus's genome is almost identical to that of a West Nile strain found in Israel last year, suggesting that it originated in the Middle East. Many now Israel last year, suggesting that it originated in the Middle East. Many now agree it has a good chance of establishing itself and spreading in the agree it has a good chance of establishing itself and spreading in the Western Hemisphere.Western Hemisphere.

Science Science 286:1450-1451. Nov. 19, 1999286:1450-1451. Nov. 19, 1999

DNA Fingerprinting of Pathogenic BacteriaDNA Fingerprinting of Pathogenic Bacteria

FIG. 1. REP-PCR fingerprints FIG. 1. REP-PCR fingerprints of food isolates of of food isolates of Listeria Listeria monocytogenes.monocytogenes.

Note the banding similarity in Note the banding similarity in the fingerprints in lanes 53-the fingerprints in lanes 53-56 and 59-63, illustrating 56 and 59-63, illustrating how identical or nearly how identical or nearly identical strains of a identical strains of a pathogen like pathogen like ListeriaListeria can be identified and tracked with great specificity.

Lane M contains molecular size Lane M contains molecular size markers.markers.

B. Jersek et al.1999. Typing of Listeria monocytogenes Strains by Repetitive Element Sequence-Based PCR. J. Clin. Microbiol. 37:103-109.

Coevolution of host and parasite: Australian rabbits and the myxoma virus

Coevolution of host and parasite: Australian rabbits and the myxoma virus

Nosocomial infections -- major sitesNosocomial infections -- major sites

Epidemiology of AIDSEpidemiology of AIDS

Epidemiology of AIDS:AIDS in men, 1993Epidemiology of AIDS:AIDS in men, 1993

Epidemiology of AIDS: AIDS in women, 1993Epidemiology of AIDS: AIDS in women, 1993

Global Health ConsiderationsGlobal Health Considerations

Leading causes of death in Leading causes of death in developeddeveloped countries countries

Leading causes of death in Leading causes of death in developingdeveloping countries countries