Foundations in Microbiology

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




                                  1
• Collecting, analyzing,
  & reporting data on
  rates of occurrence,
  mortality, morbidity
  and transmission of
  infections
• Reportable, notifiable
  diseases must be
  reported to county
  health authorities


                           2
www.cchd.org
For the state!
            3
AIDS      SNHD Reportable Diseases              Hantavirus
Amebiasis
                                                Hemolytic-uremic syncrome (HUS)
Animal bite from a rabies susceptible species
                                                Hepatitis A, B, C, delta, unspecified
Anthrax
                                                HIV infection
Botulism
                                                Influenza
Brucellosis
                                                Legionellosis
Campylobacteriosis
                                                Leptospirosis
Chancroid
                                                Listerosis
Chlamydia
                                                Lyme Disease
Cholera
                                                Lymphogranuloma Venereum
Coccidioidomycosis
                                                Malaria
Cryptosporidiosis
                                                Measles (rubeola)
Dengue
                                                Meningitis (specify type)
Diphtheria
                                                Meningococcal disease
E. coli 0157:H7
                                                Mumps
Encephalitis
                                                Pertussis
Extraordinary occurrence of illness
                                                Plague
Foodborne disease outbreak
                                                Poliomyelitis
Giardiasis
                                                Psittacosis
Gonorrhea
                                                Q Fever
Granuloma Inguinale
                                                Rabies (human or animal)
Haemophilus Influenzae (invasive)
                                                Relapsing Fever
Hansen's Disease (leprosy)
                                                Respiratory Syncytial Virus (RSV) 4
Rocky Mountain Spotted Fever
Rotavirus                       Southern Nevada
Rubella                         Health District
Salmonellosis                   Reportable Diseases
Severe Reaction to Immunization     (continued)
Shigellosis
Syphilis (including congenital)
Tetanus
Toxic Shock Syndrome
Trichinosis
Tuberculosis
Tularemia
Typhoid Fever
Yersiniosis
                                                  5
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.

                                                                     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
10
            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


                                                11
Development of Epidemiology
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                         ca 1847
• Hypothesis
   – “Germs” from autopsy cadavers infected the
     pregnant women during delivery
• Experiment
   – Physicians were to wash hands in antiseptic
     solution
                                                         13
   – Mortality significantly decreased
Selling Soap
By STEPHEN J. DUBNER and STEVEN D. LEVITT
The New York Times
September 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.”
     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

                                                       15
                   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…


                                                            16
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.

                                               17
Koch’s Postulates
Determine etiology




                     18
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



                                                                  19
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.
                                                          20
John Snow’s
Original Map




         21
Typhoid Mary - THE
Carrier
 • Mary Mallon
   – 1869 - 1938
 • Domestic servant              bacteriologist
                                                   Mary Mallon
   – Family cook                 Emma Sherman

 • Typhoid fever                     www.pbs.org/wgbh/nova/typhoid/

   – Salmonella typhi
   – Gallbladder can harbor the bacterium
   – Living reservoir for the pathogen
   – Caused several outbreaks of typhoid fever
      • 1900 to 1907
   – Fecal oral contamination
                                                               22
• 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


                                                               23
• 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
                                                         24
www.pbs.org/wgbh/nova/typhoid/
                                 25
Confinement… Medical Segregation

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

• TB sanitoriums
• Leper colonies



                                             26
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


                                                             27
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



                                                        28
Incidence during this 20 year
period = 0.67 – 0.5 = 0.17%
                                29
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

                                                                   30
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
Descriptive Epidemiology




                           32
Analytical Epidemiology
• Investigate particular causes of diseases
• Quantify risk factors




                                              33
Analytical Epidemiology




                          34
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


                                                      35
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

                                                                   36
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
                                                                   37
 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 Infants
D.M. Thea et al. 1993
N Engl J Med. 329 (23):1696-1702
                                                                38
Prospective Study




                    39
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


                                                                40
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.


                                                           41
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


                                                      42
• 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




                                                                 43
• 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


                                                           44
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
                                                        45
Types of Carriers
Inconspicuously shelters & spreads an infectious
agent




 Infected but no
 symptoms          Spread the                             Remains
                   infectious agent    Recuperating but   infected
                   during the          continue to shed   for a long
                   incubation period   infectious agent   period after
                                                          recovery


                                                                46
Passive Carrier
Contaminated but not infected
 • Direct contact
 • Indirect contact
    – Vehicle
       • Food
       • Water
       • Biological products
       • Fomites
    – Airborne
       • Droplet nuclei
       • Aerosols




                                47
Nosocomial Infections
Unique 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

                                                       48
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 49
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



                                          50
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


                             51
• Sign
  – Objective evidence of disease as noted by an
    observer


• Symptom
  – Subjective evidence of disease as sensed by the
    patient




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