Epidemiology

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Epidemiology TalaroChapter 13

The branch of medicine that deals with the study of the causes, distribution, and control of disease in populations.

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• Collecting, analyzing, & reporting data on rates of occurrence, mortality, morbidity and transmission of infections

• Reportable, notifiable diseases must be reported to county health authorities

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www.cchd.orgFor the state!

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AIDSAmebiasisAnimal bite from a rabies susceptible speciesAnthrax BotulismBrucellosisCampylobacteriosisChancroidChlamydiaCholeraCoccidioidomycosisCryptosporidiosisDengueDiphtheria E. coli 0157:H7EncephalitisExtraordinary occurrence of illness Foodborne disease outbreak GiardiasisGonorrhea Granuloma Inguinale Haemophilus Influenzae (invasive)Hansen's Disease (leprosy)

HantavirusHemolytic-uremic syncrome (HUS)Hepatitis A, B, C, delta, unspecifiedHIV infection InfluenzaLegionellosisLeptospirosisListerosisLyme DiseaseLymphogranuloma Venereum MalariaMeasles (rubeola)Meningitis (specify type)Meningococcal diseaseMumps PertussisPlaguePoliomyelitisPsittacosis Q Fever Rabies (human or animal)Relapsing FeverRespiratory Syncytial Virus (RSV)

SNHD Reportable Diseases

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Rocky Mountain Spotted FeverRotavirusRubella SalmonellosisSevere Reaction to ImmunizationShigellosisSyphilis (including congenital) TetanusToxic Shock SyndromeTrichinosisTuberculosisTularemiaTyphoid Fever Yersiniosis

Southern Nevada Health District Reportable Diseases (continued)

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Report Diseases to the following numbers:

Disease Phone Fax

HIV/AIDS (702) 759-0702 (702) 868-2825

Sexually Transmitted Diseases (702) 759-0705 (702) 383-1446

Tuberculosis (702) 759-1369 (702) 633-0975

Other Reportable Diseases (702) 759-1300 (702) 383-4936

Foodborne Illness Outbreaks (702) 759-1300 (702) 383-4936

Reports must include the name, address, telephone number, age, date of birth, sex, race, occupation, diseases, date of onset, date of diagnosis and any other available information requested by the Health Authority.

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Centers for Disease Control and Prevention (CDC)

Atlanta, GA (www.cdc.gov)

Principal government agency responsible for keeping track of infectious diseases in the U.S.

For the Country…

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www.cdc.gov/ncidod/eid/index.htm

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www.cdc.gov/mmwr/

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For the World…

The WHO – The World Health Organization- a part of the United Nations- www.who.int/en-monitors the world- recent story… confirmed case of H5N1 influenza in Egypt… 4 year old girl with confirmed exposure to dead birds… patient stable… 15 fatalities out of 36 cases thus far in Egypt

Development of Epidemiology

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Ignaz Semmelweiss (1818-1865)• Hungarian physician was working in a Viennese

maternity hospital

• Two separate clinics

– Babies were delivered by physicians

• High mortality rate of mothers (childbed fever)

– Babies delivered by midwives

• Low mortality rate

• Hypothesis

– “Germs” from autopsy cadavers infected the pregnant women during delivery

• Experiment

– Physicians were to wash hands in antiseptic solution

– Mortality significantly decreased

ca 1847

Selling Soap By STEPHEN J. DUBNER and STEVEN D. LEVITTThe New York TimesSeptember 24, 2006

“In one Australian medical study, doctors self-reported their hand-washing rate at 73 percent, whereas when these same doctors were observed, their actual rate was a paltry 9 percent.”

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Joseph Lister (1827-1912)

Common complaint… “Operation successful… but the patient died!”

Most surgical patients died of sepsis (infections)…

~1865 started “aseptic surgery” to prevent infection (or putrefaction)…

Cleaned wounds etc. with carbolic acid (phenol)… “carbolic spray” invented in 1869

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Robert Koch About 1878 – Koch was demonstrating the use of steam for killing

bacteria on surgical instruments

Early 1880’s - Discovered the causative agent of tuberculosis (consumption) (at the time ~1/7 of all reported human deaths attributed to this disease -1860s to 1940s)… also developed the precursor to the acid-fast stain

Now… WHO reports that 30 million people could die from TB in the next decade… TB remains the leading infectious killer of youth and adults… estimatees that 1/3 of the world’s population is infected.

Now… MDR-Mycobacterium tuberculosis…

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Koch’s Postulates ca 1884

Determine etiology

1. Find evidence of a particular microbe in every case of a disease.

2. Isolate that microbe from an infected subject and cultivate it artificially in the laboratory.

3. Inoculate a susceptible healthy subject with the laboratory isolate and observe the resultant disease.

4. Reisolate the infectious agent from the test subject.

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Koch’s PostulatesDetermine etiology

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Epidemiology

• Involves identification of pathogen, reservoir of the pathogen, and mode of transmission

• John Snow was first true epidemiologist• Studied 1854 cholera outbreak in London• Analyzed death records, obtained information on victims, interviewed survivors• Realized afflicted obtained water from single source• Removal of the contaminated water pump reduced number of cases

• Father of Epidemiology

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John Snow

Memorial & Pub on Broadwick Street(Was called Broad street in 1854)

Documented that water companies pumped from sewagecontaminated areas of the Thames river.

Vibrio cholerae

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John Snow’s Original Map

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Typhoid Mary - THE Carrier

• Mary Mallon– 1869 - 1938

• Domestic servant– Family cook

• Typhoid fever– Salmonella typhi– Gallbladder can harbor the bacterium– Living reservoir for the pathogen– Caused several outbreaks of typhoid fever

• 1900 to 1907 – Fecal oral contamination

Mary Mallon

www.pbs.org/wgbh/nova/typhoid/

bacteriologist

Emma Sherman

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• Incarcerated by New York health officials– Riverside Hospital on North Brother Island the East River near the Bronx

• No trial• Sections 1169 and 1170 of the Greater New York

Charter– The board of health shall use all reasonable means for

ascertaining the existence and cause of disease or peril to life or health, and for averting the same, throughout the city. [Section 1169]

– Said board may remove or cause to be removed to [a] proper place to be by it designated, any person sick with any contagious, pestilential or infectious disease; shall have exclusive charge and control of the hospitals for the treatment of such cases. [Section 1170]6

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• Ms. Mallon sued for her release in 1909– The court ruled in favor of New York

• Ms. Mallon was released in 1910– Signed an affidavit promising never to cook again

• Typhoid fever outbreak at the Sloane Maternity Hospital in Manhattan during 1915– 25 people became ill and 2 of them died– Ms. Mallon was the cook– Alias was Mrs. Brown

• Confined to Riverside Hospital on North Brother Island

• Employed at the hospital• Died in 1938

25www.pbs.org/wgbh/nova/typhoid/

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Confinement… Medical Segregation

• Were TB sanatoriums and leprosy colonies effective methods at controlling the disease?

• TB sanitoriums

• Leper colonies

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Epidemiology• Descriptive

– Describe the occurrence of disease in populations

• Analytical– Identify & explain the causes of disease– Risk factors

• The two are interrelated– Description Analytical– Analytical Descriptive– Many epidemiological studies are hybrids of the descriptive &

analytical methods

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There are two important measures in epidemiology

• Prevalence – The fraction (proportion) of current living individuals

in a population who have a disease or infection at a particular time

• Incidence – The proportion of a population that develops new cases

of a disease or infection during a particular time

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Incidence during this 20 year period = 0.67 – 0.5 = 0.17%

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Descriptive Epidemiology• Collection of all data describing the occurrence of disease• Person

• Disease predominates in smokers• Disease predominates immunocompromised individuals

• Place• Disease is associated with an arid climate• Disease is associated with a tropical climate

• Time• Disease is associated with the date of the company picnic• A particular year

• Clustering• An unusually high incidence or prevalence of a disease in a subpopulation

Clustering & Legionnaire’s Disease

The disease was first described in elderly members of the American Legion (person), who attended the annual meeting at a hotel in Philadelphia (place) during the summer of 1976 (time).

Bacterial respiratory infection caused by Legionella pneumophila

Legionnaire’s Disease was clustered byPersonPlaceTime

Descriptive Epidemiology

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Descriptive Epidemiology

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Analytical Epidemiology• Investigate particular causes of diseases• Quantify risk factors

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Analytical Epidemiology

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• Experimental / Interventional Studies– A condition of an experimental subpopulation is

changed & effect on the development of the disease is observed

– Results are compared with the main population or an untreated population• Test a vaccine on a subgroup• Determine the prevalence of the disease• Compare with untreated population

Analytical Epidemiology

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Analytical Epidemiology• Observational Studies• Within any population, some individuals will develop a disease but others will not• Epidemiologist subdivides the population according to risk factors

• Smokers versus nonsmokers• Obese versus normal weight• Diabetics versus healthy

• Case Control Studies• Involves studying a group of individuals with a particular disease (the cases) and comparing them with a group of unaffected individuals (the controls).

• Particularly useful if the disease is rare• 1 / 1,000,000 200 cases in the country • Also useful for new diseases

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Analytical Epidemiology

• Cohort Studies• Involves studying a group of individuals that share a particular risk factor for a disease.• The group is examined for the frequency or rate of disease appearance in comparison with a control population that does not have the risk factor• Implicate or eliminate a risk factor• Prospective

• Forward in time• Identify a cohort and follow these individuals over time

• Retrospective• Go back in time• A risk factor is defined and a cohort of individuals is identified

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Eight year prospective study of HIV infection in a cohort of homosexual men--clinical progression, immunological and virological markers.R.K. Lau et al. 1992

Int J STD AIDS. 3(4):261-6.

Prospective Study

A prospective study of the risk of tuberculosis among intravenous drug users with human immunodeficiency virus infection.P.A. Selwyn et al. 1989N Engl J Med. 321 (18):1268

A Prospective Study of Diarrhea and HIV-1 Infection among 429 Zairian InfantsD.M. Thea et al. 1993 N Engl J Med. 329 (23):1696-1702

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Prospective Study

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Retrospective Study

HIV retrospective study of the German Red Cross blood donation service in Germany.Gluck, D. et al. 1994. Infusionsther Transfusionsmed. 21(6):368-75

SHORT REPORT

Retrospective cohort study examining incidence of HIV andhepatitis C infection among injecting drug users in Dublin.B P Smyth et al. 2003 J Epidemiol Community Health 57:310–311

AIDS and Thrombosis: Retrospective Study of 131 HIV-Infected PatientsSaif, et al. 2001AIDS Patient Care and STDs 15 (6): 311-320

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Definitions• Infection

– A condition in which pathogenic microbes penetrate host defenses, enter tissues & multiply.

• Disease – Any deviation from health, disruption of a tissue or

organ caused by microbes or their products.

• Sequelae – Long-term or permanent damage to tissues or organs.

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Definitions• True pathogens

– Capable of causing disease in healthy persons with normal immune defenses• Influenza virus, plague bacterium, malarial protozoan

• Opportunistic pathogens – Cause disease when the host’s defenses are compromised

• Candida albicans• Pseudomonas aeruginosa

– Cystic fibrosis patients– Burn patients

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• Etiology– Determine the cause of the infectious disease

– Etiologic or causative agent

• Mortality rate – The total number of deaths in a population due to a certain disease

• Morbidity rate – Number of people afflicted with a certain disease

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• Endemic – Disease that exhibits a relatively steady frequency over a

long period of time in a particular geographic locale

• Sporadic – Occasional cases are reported at irregular intervals

• Epidemic – Incidence/outbreak of a disease beyond what is expected

• Pandemic – Epidemic across continents

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Reservoirs of Infection• Primary habitat in the natural world from which a

pathogen originates• Living reservoirs may or may not have symptoms

– Asymptomatic carriers

– Passive carriers

– Vectors

• Live animal that transmits infectious disease

• Nonliving reservoirs – Soil

– Water

– Food

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Types of CarriersInconspicuously shelters & spreads an infectious agent

Infected but nosymptoms Spread the

infectious agent during the incubation period

Recuperating butcontinue to shedinfectious agent

Remains infectedfor a long period afterrecovery

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Passive CarrierContaminated but not infected

• Direct contact• Indirect contact

– Vehicle • Food• Water• Biological products• Fomites

– Airborne • Droplet nuclei• Aerosols

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Nosocomial InfectionsUnique Example of Transmission

• Diseases that are acquired during a hospital stay• Most commonly involve urinary tract, respiratory tract, &

surgical incisions• Most common organisms involved Gram-negative intestinal

flora– Escherichia coli – Pseudomonas spp.– Staphylococcus spp.

• On average 5% of all patients acquire a nosocomial infection– 8 million additional days of hospitalization– Increase cost of $5 – 10 billion dollars

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Nosocomial InfectionsControl Nosocomial InfectionsDisinfectionMedical asepsisHand asepsis

BathingSanitary handling of foodSanitary handling of bodily fluidsSurgical asepsisSterile proceduresIsolation of contagious patientsIsolation of susceptible patients

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Patterns of Infection• Localized infection

– Microbes enters body & remains confined to a specific tissue

• Systemic infection– Infection spreads to several

sites and tissue fluids usually in the bloodstream

• Focal infection– Infectious agent breaks loose

from a local infection and is carried to other tissues

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Patterns of Infection• Mixed Infection

– Several microbes grow simultaneously at the infection site

• Primary Infection – Initial infection

• Secondary Infection – Another infection by a

different microbe

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• Sign – Objective evidence of disease as noted by an

observer

• Symptom – Subjective evidence of disease as sensed by the

patient