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Epidemiology

Talaro Chapter 13. Epidemiology. The branch of medicine that deals with the study of the causes, distribution, and control of disease in populations. Collecting, analyzing, & reporting data on rates of occurrence, mortality, morbidity and transmission of infections

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Epidemiology

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  1. Talaro Chapter 13 Epidemiology The branch of medicine that deals with the study of the causes, distribution, and control of disease in populations.

  2. Collecting, analyzing, & reporting data on rates of occurrence, mortality, morbidity and transmission of infections • Reportable, notifiable diseases must be reported to county health authorities

  3. www.cchd.org For the state!

  4. SNHD Reportable Diseases 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)

  5. Rocky Mountain Spotted FeverRotavirusRubella SalmonellosisSevere Reaction to ImmunizationShigellosisSyphilis (including congenital) TetanusToxic Shock SyndromeTrichinosisTuberculosisTularemiaTyphoid Fever Yersiniosis Southern Nevada Health District Reportable Diseases (continued)

  6. 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…

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

  8. www.cdc.gov/mmwr/

  9. 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

  10. Development of Epidemiology

  11. 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

  12. Selling SoapBy 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.”

  13. 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

  14. 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…

  15. Koch’s Postulates ca 1884Determine etiology • Find evidence of a particular microbe in every case of a disease. • Isolate that microbe from an infected subject and cultivate it artificially in the laboratory. • Inoculate a susceptible healthy subject with the laboratory isolate and observe the resultant disease. • Reisolate the infectious agent from the test subject.

  16. Koch’s PostulatesDetermine etiology

  17. 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

  18. John Snow Vibrio cholerae Memorial & Pub on Broadwick Street (Was called Broad street in 1854) Documented that water companies pumped from sewage contaminated areas of the Thames river.

  19. John Snow’s Original Map

  20. 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 bacteriologist Emma Sherman Mary Mallon www.pbs.org/wgbh/nova/typhoid/

  21. 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

  22. 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

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

  24. Confinement… Medical Segregation • Were TB sanatoriums and leprosy colonies effective methods at controlling the disease? • TB sanitoriums • Leper colonies

  25. 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

  26. 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 There are two important measures in epidemiology

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

  28. 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

  29. Descriptive Epidemiology Clustering & Legionnaire’s Disease Bacterial respiratory infection caused by Legionella pneumophila 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). Legionnaire’s Disease was clustered by Person Place Time

  30. Descriptive Epidemiology

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

  32. Analytical Epidemiology

  33. Analytical Epidemiology • 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

  34. 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

  35. 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

  36. Prospective Study • 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. A prospective study of the risk of tuberculosis among intravenous drug users with human immunodeficiency virus infection. P.A. Selwyn et al. 1989 N 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

  37. Prospective Study

  38. 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 Retrospective cohort study examining incidence of HIV and hepatitis C infection among injecting drug users in Dublin. B P Smyth et al. 2003 J Epidemiol Community Health 57:310–311 SHORT REPORT AIDS and Thrombosis: Retrospective Study of 131 HIV-Infected Patients Saif, et al. 2001 AIDS Patient Care and STDs 15 (6): 311-320

  39. 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. Definitions

  40. 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 Definitions

  41. 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

  42. 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

  43. 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

  44. Types of CarriersInconspicuously shelters & spreads an infectious agent Infected but no symptoms Spread the infectious agent during the incubation period Remains infected for a long period after recovery Recuperating but continue to shed infectious agent

  45. Passive CarrierContaminated but not infected • Direct contact • Indirect contact • Vehicle • Food • Water • Biological products • Fomites • Airborne • Droplet nuclei • Aerosols

  46. 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

  47. Nosocomial Infections Control Nosocomial Infections Disinfection Medical asepsis Hand asepsis Bathing Sanitary handling of food Sanitary handling of bodily fluids Surgical asepsis Sterile procedures Isolation of contagious patients Isolation of susceptible patients

  48. 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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