Docstoc

STAT 6395

Document Sample
STAT 6395 Powered By Docstoc
					Spring , 2008




                       STAT 6395
                Special Topic in Statistics:
                      Epidemiology




                                          Filardo and Ng, 2008
I. Epidemiology


The study of the distribution and determinants of health-
related states or events in specified populations and the
translation of study results to control health problems
Distribution
                        • Persons affected
                        • Place
                        • Time




Epidemiology: The study of the distribution and determinants of health-related
states or events in specified populations and the translation of study results to
control of health problems
Determinants
All the physical, biological, social, cultural, and behavioral
factors that influence health




Epidemiology: The study of the distribution and determinants of health-related
states or events in specified populations and the translation of study results to
control of health problems
Health-related states or events
    •   Diseases
    •   Mortality (death)
    •   Specific causes of death
    •   Injuries
    •   Disability
    •   Health-related behaviors
    •   Physiological measurements
    •   Results of preventive regimens
    •   Clinical outcomes
    •   Provision and use of health services



Epidemiology: The study of the distribution and determinants of health-related
states or events in specified populations and the translation of study results to
control of health problems
Specified populations

       • Residents of a defined geographic area
       • Students who attend a specified school
       • Persons who belong to a specified organization
       • Workers at a specified workplace




Epidemiology: The study of the distribution and determinants of health-related
states or events in specified populations and the translation of study results to
control of health problems
Translation
                               Study Results

             Scientific articles and presentations at meetings

                             Clinical guidelines

            Prevention programs
            Quality of care improvement programs
            Patient safety programs




Epidemiology: The study of the distribution and determinants of health-related
states or events in specified populations and the translation of study results to
control of health problems
Control
      Operations or programs aimed at reducing the
      adverse impact of the disease on the community

                  1)    Prevention
                  2)    Cure
                  3)    Management




Epidemiology: The study of the distribution and determinants of health-related
states or events in specified populations and the translation of study results to
control of health problems
  Primary prevention

          An action taken to prevent the development
          of a disease in a person who is well and does
          not have the disease in question




Operations or programs aimed at reducing the adverse impact of the disease on
the community: 1) Prevention; 2) Cure; 3) Management
  Secondary prevention
  (Cure and management)
          The identification and treatment of people
          who have already developed a disease or
          precursors of the disease, through screening,
          at an early enough stage in the disease’s
          natural history (early detection) such that
          intervention will be more effective than if the
          disease had been discovered later


Operations or programs aimed at reducing the adverse impact of the disease on
the community: 1) Prevention; 2) Cure; 3) Management
II. Objectives of Epidemiology

 • To describe the extent of disease in the community
 • To identify risk factors (factors that influence a person’s risk of acquiring a
    disease) for disease and the etiology or cause of disease

 • To study the natural history (course from onset to resolution) and
    prognosis of disease

 • To evaluate both existing and new preventive and therapeutic measures
    (including health care delivery)

 • To provide the foundation for developing public policy and regulatory
    decisions relating to environmental problems
…bottom line, Epidemiology research
requires a multidisciplinary effort and
statisticians play a key role in:

       • Hypothesis development
       • Study execution
Hypothesis development
       Epidemiologists study the specific distribution and
       determinants of specific diseases

       Development of hypotheses to test in an
       epidemiologic study requires in-depth knowledge of
       the disease and determinants under study
           • Medical and biological sciences
            • Social and behavioral sciences




Epidemiology Research  hypothesis development and study execution
Study execution

             • Statistics ------------>Biostatistics
             • Medical and biological sciences
             • Social and behavioral sciences




Epidemiology Research  hypothesis development and study execution
Biostatistics
              • Separate chance observations from
                 meaningful observations
              • Sampling
              • Sophisticated statistical analyses




Epidemiology Research  Biostatistics, medical and biological sciences, social
                        and behavioral sciences
Medical and biological sciences
     • Microbiology, e.g., to identify infectious agents
     • Clinical medicine and pathology, (e.g., to identify
        cases of disease)
     • Molecular biology, (e.g., to identify genotype of
        individuals)
     • Biochemistry, (e.g., to measure serum hormone
        levels)




Epidemiology Research  Biostatistics, medical and biological sciences, social
                        and behavioral sciences
Social and behavioral science

       • Design questionnaires for obtaining valid
          information
       • Design effective interventions for lifestyle
          changes




Epidemiology Research  Biostatistics, medical and biological sciences, social
                        and behavioral sciences
Epidemiology Sub-disciplines

       • Disease-specific subject matter
       • Exposure-specific subject matter
       • Health services research
Disease-specific subject matter
    • Infectious disease epidemiology
          • HIV/AIDS epidemiology
          • Malaria epidemiology
    • Chronic disease epidemiology
         • Cancer epidemiology
         • Cardiovascular epidemiology
         • Perinatal epidemiology
         • Neuroepidemiology
         • Psychiatric epidemiology

Epidemiology disciplines  Disease-specific subject matter, Exposure-specific
                           subject matter, Health services research
Determinant (exposure)-specific subject
matter
              •   Environmental epidemiology
              •   Occupational epidemiology
              •   Pyschosocial epidemiology
              •   Genetic epidemiology
              •   Nutritional epidemiology
              •   Pharmacoepidemiology



Epidemiology disciplines  Disease-specific subject matter, Exposure-specific
                           subject matter, Health services research
Health services research
        • Operations    research: the study of the
           placement of health services in the community
           and the optimum utilization of such services
        • Program evaluation
        • Clinical epidemiology or outcomes research:
           the study of illness outcomes in persons seen
           by providers of health care; evaluation of
           medical treatments



Epidemiology disciplines  Disease-specific subject matter, Exposure-specific
                           subject matter, Health services research
Types of epidemiologic studies

     • Experimental
     • Observational (this course will focus on
       this second type of studies)
Experimental Studies
       • Studies in which conditions are under the control of
          the investigator(s).

       • The investigators assigns subjects to different
          study groups. The effect of the treatment is
          determined by comparing the outcome of interest
          in these groups.




Type of studies  Experimental, Observational
Experimental studies (examples)

       • Randomized clinical trial (unit of study is the
          individual)

       • Community trial (unit of study is the community)




Type of studies  Experimental, Observational
Observational studies
       • Studies in which the investigators does not control
          conditions, but rather observe nature taking its
          course by gathering information, recording,
          classifying, counting, and analyzing the collected
          data.

       • Exposure and disease outcomes would have
          occurred whether or not the studies have been
          performed because there were no ‘a priori’
          intervention(s) on the part of the investigators.


Type of studies  Experimental, Observational
Observational studies (examples)

                       • Descriptive
                       • Analytic




Type of studies  Experimental, Observational
Descriptive studies

     Studies aimed at describing the distribution of disease
     or other health-related variables with respect to person
     (age, gender, race, socioeconomic status), place
     (census tract, county, state, country, urban/rural), and
     time (season, year)




Type of studies  Experimental, Observational (descriptive)
Descriptive studies

        • Often use routinely-collected data
        • Can define high-risk groups
        • Can be used for hypothesis generation, but
           generally not hypothesis testing




Type of studies  Experimental, Observational (descriptive)
Analytic studies
        • Test specific etiologic hypotheses
        • To generate new etiologic hypotheses
        • To suggest mechanisms of causation
        • To generate preventive hypotheses
        • To suggest or identify potential methods for
           disease prevention

In these studies, the epidemiologist observes the relationship between an exposure
and a disease or other health outcome.

Type of studies  Experimental, Observational (analytic)
Definition: Exposure
           A potential causal agent or characteristic, such as
           infectious agent, behavior, dietary factor,
           medication, medical treatment, genetic makeup,
           environmental agent, or physiologic state (e.g.,
           serum level of a hormone or nutrient; blood
           pressure).



                     An exposure may be harmful or beneficial


Type of studies  Observational  Analytic
Types of analytic studies

       • Cohort studies
       • Case-control studies




Type of studies  Observational
Cohort studies

 A study in which a group of                       and compared with respect
 persons exposed to a factor                       to the incidence rate of the
 of interest and a group of                        disease or other condition of
 persons not exposed are                           interest
 followed



                                  Time



Type of studies  Observational  Cohort studies
Cohort studies (study schema)




Type of studies  Observational  Cohort studies
Case-Control studies

        Studies in which a group of persons with a disease
        (cases) and a comparison group of persons without
        the disease (controls) are compared with respect to
        the history of past exposures to factors of interest


              Past                                Present



Type of studies  Observational  Case-Control
Case-Control studies (study schema)




Type of studies  Observational  Case-Control
Time
Either descriptive or analytic studies

     • Cross-sectional studies
     • Ecologic studies




Type of studies  Observational
Cross-sectional studies

       Studies of the distribution of exposures
       and/or disease in a defined population
       at one given point in time




Type of studies  Observational  Cross-sectional
Ecologic studies
       Studies of the association between exposures and
       disease in which the units of analysis are
       populations or groups of people, rather than
       individuals.

       This involves the assessment of the correlation of
       exposure rates and disease rates among different
       groups or populations.

                          Causality, though???


Type of studies  Observational  Ecologic
Types of Epidemiologic studies
Example involving several
types of study designs

   Ecologic study results
   Case-Control study
   results

   Cohort study results



   Randomized controlled trial
   results
Which type of study is the ‘Gold Standard’
and/or more common/feasible?

     Experimental                       Observational
          controlled setting              real life setting
(difficult to reproduce in real life)



         Efficacy                       Effectiveness
            Focus of this course is on

observational Epidemiologic research
 (research regarding the direct study of disease in human populations)
Some triumphs of observational
Epidemiology

 • Smoking causes lung cancer
 • Identification of cardiovascular disease risk factors
 • Characterization of how HIV spreads through a
   population
 • Identification of occupational hazards (e.g., asbestos)
Three ‘Eras’ of Epidemiology

    • Sanitary (1800-1875)
    • Infectious disease (1875-1950)
    • Chronic disease (1950-present)
Sanitary ‘Era’ (1800-1875)
• Miasma theory of disease – poisoning by foul emanations (miasma) from the
   soil, water, and air.
• Created national vital statistics systems: much valuable descriptive
   epidemiology
• Demonstrated clustering of disease in slums and among the poor
• Solutions – sewage systems, drainage, clean water supplies, garbage
   collection, decent housing
• Incorrect miasma theory, but solutions were a major contribution to public
   health

                          Lesson:
prevention doesn’t necessarily require understanding of cause



Sanitary, Infectious disease, Chronic disease
Infectious disease ‘Era’ (1875-1950)
   • Germ theory: single microscopic agents relate one-to-
       one to specific diseases

   • Epidemiology took a back seat to laboratory science,
       although in the1920s-30s, the germ theory was
       broadened to accommodate the interactive roles of
       host (immune and nutritional status), environment, and
       agent in infectious disease
   • Other epidemiologic contributions:
     – Occupational exposures as causes of cancer
     – Specific vitamin deficiencies as causes of disease


Sanitary, Infectious disease, Chronic disease
Chronic Disease (Modern) ‘Era’
   • By end of World War II, infectious diseases were under
       control in the developed countries; coronary heart
       disease and lung cancer were epidemic

   • Multifactor causation of chronic disease
   • Focus on identification and control of risk factors at the
       individual level

   • Black box approach: emphasis on risk factor
       identification with only a secondary concern about
       mechanism or pathogenesis
              Most of the methodology we will cover in this course
                   was developed during this ‘Modern Era’.

Sanitary, Infectious disease, Chronic disease
New ‘Era’(???)
• Emerging infectious diseases (e.g., HIV)
• Continued burden of infectious diseases in majority of world
• Traditional chronic disease epidemiology has hit a wall in its ability to
    discover important new risk factors

• Advances in molecular biology and genetics allow the study of
    pathogenesis and causality at the molecular and genetic levels using
    epidemiologic approaches

• The need to be concerned with causal pathways at multiple levels,
    including the societal level, as opposed to an exclusive focus on risk
    factors at the individual level, has become apparent to many




Sanitary, Infectious disease, Chronic disease, ???
Levels of causality

        • Societal or population
        •   Individual
        •   Biochemical
        •   Cellular
        •   Molecular
What causes lung cancer?
     Individual/societal:   Cigarette    smoking   (nicotine
      addiction)

     Biochemical: Specific chemicals in cigarette smoke
      that cause the mutations

     Cellular: Specific phenotypic changes in the cells
      that result in loss of growth control

     Molecular: Mutations in DNA
What causes AIDS?
   Societal:
     Poverty
     Prostitution
   Individual/societal: a. Multiple sexual partners;
                        b. Intravenous drug use
  X Biochemical:
   Cellular: Infection -the HIV viruses progressively
    destroy lymphocytes (a types of white blood cells)

   Molecular: Mutations in DNA -the viral DNA is
    incorporated into the DNA of the infected lymphocyte
On the mode of communication of cholera
            John Snow, M.D.
             London, 1855
John Snow
   1857
Why study Snow?
 • Appreciate those who came before us and paved
   the way

 • Brilliant piece of work: lucid and thorough
 • Snow’s work on cholera illustrates a key
   epidemiologic principle:

…the most important information to have about any
communicable disease is its mode of communication
John Snow (1813-1858)
   • Physician
   • Pioneer    in  both    epidemiology    and
     anesthesiology

   • Experiments in administration of anesthesia
     himself may have contributed to his early
     death
Snow administered
chloroform to
Queen Victoria
for the birth of
Prince Leopold and
Princess Beatrice
Cholera: Acute Gastrointestinal Disease
  • Incubation period: 12-72 hours
  • Sudden onset of severe vomiting
  • Followed shortly by voluminous, watery, non-bloody
    diarrhea, described as rice water stool (white and
    opalescent)
  • Abdominal cramps
  • Severe cases: severe dehydration, circulatory
    collapse, renal failure (death may occur within a few
    hours of first symptoms)
  • Case fatality rate may range from 1-50%, depending
    on strain of Vibrio cholerae and treatment
                In 1817,
 four years after John Snow’s birth,
  cholera emerged from the Indian
subcontinent, where it had existed for
centuries, to spread across the world.
Cholera Epidemics in Great Britain
     • 1831-32
        – 56,000 deaths

     • 1848-49
        – 125,000 deaths

     • 1853-54
        – Cholera returns to England
Cholera: Apparently contradictory facts in
1854
  • Local spread with evidence of direct communication
    from person to person
  • Failure to spread to many in close contact with the
    sick
  • Cases occur without traceable relation to prior cases
  • Highest rates in low-lying areas and in filthy
    environments
        - Exceptions too numerous to be disregarded
  • Unpredictability of its spread around the world and
    its geographic distribution
Cholera: Miasma Theory
   Report of the London General Board of Health on
   cholera epidemic of 1848-49:
   “…it appears as if some organic matter, which
   constitutes the essence of the epidemic, when
   brought in contact with other organic matter
   proceeding      from     living   bodies,     or   from
   decomposition, has the power of so changing the
   condition of the latter as to impress it with poisonous
   qualities of a peculiar kind similar to its own.”
Cholera: Elaborations of Miasma theory
  • Localizing influences
  • Predisposition
  • Spontaneous generation of “cholera poison”
  • “Poison” spread by diffusion through              the
    atmosphere vs. poison attached itself to solid bodies
  • “Poison” communicated by an effluvium (contagion)
    given off by the sick
William
Farr
Farr’s elaboration of Miasma theory
  • Soil at low elevations, especially near the banks of the
    Thames River, contained much organic matter that
    produced deadly miasmata.
  • Miasmata diffused through the atmosphere in a cloud or
    mist
  • Concentration of miasmata would be greater at lower
    elevations than in higher elevations, accounting for the
    geographic distribution in the London epidemic of 1849.

  Farr’s theory did have some consistency with the facts.
John Snow’s Germ Theory
 • Cholera caused by a germ cell, not yet identified

 • 2 main modes of transmission of germ cell, which was
   found in the evacuations of cholera victims:
       1. Drinking water contaminated with sewage
       2. Contaminated food, bedding, or clothing



Snow was firmly convinced of his theory by start of
               1853-54 epidemic.
Snow’s ecologic observations prior to the
1853-54 epidemic

 Cholera “has never appeared except where there
has been ample opportunity for it to be conveyed by
              human connections.”
 • Epidemics of cholera followed major routes of
   commerce and warfare.
 • Cholera always appeared first at seaports, when
   extending to a new island or continent.
Snow’s observations from ‘case’ histories
 • Cholera can be communicated from the sick to the
   healthy.
 • Persons attending those with cholera do not necessarily
   become afflicted.
 • Close contact with a cholera patient is not necessary to
   become afflicted.


               Snow’s conclusion:
“…cholera is communicated from person to person,
              but not through the air”
When cholera returned to London in
August 1853, Snow had a definite
hypothesis:

      cholera was spread by
       contaminated water.
Water supply of south districts of London
 Lambeth Water Company
 • Until 1852, drew water from the Thames River in
   London, contaminated with London’s sewage
 • In 1852, moved intake 22 miles up river and far from the
   contaminated water


 Southwark and Vauxhall Water Company
 • Continued to draw water from the contaminated Thames
 Water           1849          1853-54
Company        Epidemic       Epidemic
 Lambeth      Contaminated      Pure
                (London)      (Up River)

Southwark &   Contaminated   Contaminated
 Vauxhall       (London)       (London)
Cholera Deaths in South Districts
of London
                    Deaths/100,000
                        Epidemic
   Water Company 1849         1853
   S&V, Lambeth  1290         61
   S&V          1420          94
   S&V, Kent    2050        107
Cholera deaths (per 100,000) in south
districts of London
  District              Water supply   1849        1853
  Bermondsey            S&V            1610         150
  St. Saviour           S&V, Lam       1530         146
  St. George            S&V, Lam       1640         143
  St. Olave             S&V            1810         134
  Rotherhithe           S&V, Kent      2050         112
  Newington             S&V, Lam       1440          57
  Wandsworth            S&V, others    1000          51
  Camberwell            S&V, Lam        970          40
  Lambeth               Lam, S&V       1200          34


  Notes: 1. Lambeth was supplied mostly by Lambeth Water Co.
         2. Rotherhithe supplied partly by Kent in 1853
 Cholera Deaths in south districts of
 London, 1853, sub-district analysis
     Water                  Cholera   Deaths/
     Supply    Population   Deaths    100,000
     S&V        167,654        192        116
     Lambeth     14,632          0         0
     Both       301,149         182       60


How many cholera deaths would we expect in
sub-districts supplied by Lambeth if they had the
same death rate as those supplied by S&V?
Cholera Deaths in south districts of
London, 1853, sub-district analysis
  Water                 Cholera         Deaths/
  Supply  Population    Deaths          100,000
  S&V      167,654         192              116
  Lambeth   14,632           0                0
  Both     301,149         182               60


   Expected deaths for Lambeth = (116/100,000)*14,632 = 16
Additional Observations on Sub-districts:
  • Among the sub-districts supplied by both companies,
    those supplied mainly by Lambeth had a low death rate,
    while those supplied mainly by S&V had a high death
    rate.
  • Two sub-districts supplied only by S&V also contained a
    number of pump-wells. These sub-districts had a low
    death rate.
By the return of cholera in July 1854, Snow recognized the full
significance of the intermixing of the water supplies of the 2
companies


   “…in the sub-districts … supplied by both Companies,
   the mixing of the supply is of the most intimate kind… A
   few houses are supplied by one Company and a few by
   the other, according to the decision of the owner or
   occupier at that time when the Water Companies were
   in active competition …”
By the return of cholera in July 1854, Snow recognized
the full significance of the intermixing of the water
supplies of the 2 companies

   “…in many cases a single house has a supply different
   from that on either side. Each company supplies both
   rich and poor, both large houses and small; there is no
   difference either in the condition or occupation of the
   persons receiving the water of the different Companies.”
An Experiment on the Grandest Scale


  “…no fewer than three hundred thousand people of both
  sexes, of every age and occupation, and of every rank
  and station, from gentlefolks down to the very poor,
  were divided into two groups without their choice …”
An Experiment on the Grandest Scale

  “…one group being supplied with water containing the
  sewage of London,

  …the other group having water quite free from such
  impurity”
What type of study John Snow conducted?
What type of study John Snow conducted?
Cohort Study
  • A study in which a group of persons exposed to a factor
    of interest and a group of persons not exposed are
    followed and compared with respect to the incidence
    rate of the disease or other condition of interest.
  • Exposed group: persons using S&V water supply
  • Comparison group: persons using Lambeth water
    supply


 Compared cholera mortality rates in the two groups
Calculation of mortality rates required
numerators and denominators
                           Mortality rate in exposed group
                                          =
     (Cholera deaths among persons supplied with S&V water) / (Number of persons supplied with S&V water)




                        Mortality rate in comparison group
                                         =
 (Cholera deaths among persons supplied with Lambeth water) / (Number of persons supplied with Lambeth water)




         To determine numerators and denominators,
      Snow needed a way to classify each death and every
           person in the population by water supply
The Numerators
 • For each cholera death in the relevant districts, Snow
   obtained information on the water supply

 • “The inquiry was necessarily attended with a good
   deal of trouble.”

 • Chemical test problematic because S&V water had 40
   times more NaCl than Lambeth
The Denominators
“ …a return had been made to Parliament of the entire
number of houses supplied with water by each of the Water
Companies, but ... the number of houses which they supplied
in particular districts was not stated…”

 • Therefore Snow had to include all the south districts of
   London in his study, not just the districts where the
   water supply was intermingled.

                 A daunting undertaking,
        so Snow obtained an assistant (Mr. Whiting)
Cholera deaths in south London districts during first 4 weeks of
1854 Epidemic, by water supply
                                          Deaths/
     Water         Cholera                10,000
     Supply        Deaths    Houses       Houses
     S&V            286      40,046         71.4
     Lambeth          14     26,107          5.4
                               Relative risk = 71.4/5.4 ≈ 13.2
     Thames          22
     Pump-wells        4
     Ditches           4
     Unknown           4
     London         277      287,345          9.6
     (-S&V)
              Note: Houses, not persons, used in denominator
More data …
“ …as the epidemic advanced, the disproportion between the
number of cases in houses supplied by the Southwark and
Vauxhall Company and those supplied by the Lambeth
Company, became not quite so great, although it continued
very striking…”

 • Cholera likely was imported from Baltic Fleet to
   Thames River, which was initially the primary source
   of the epidemic

 • Later, cholera was also spread by other means,
   diluting the water company effect
Cholera deaths in south London districts during first 7 weeks of
1854 Epidemic, by water supply
                                      Deaths/
     Water      Cholera               10,000
     Supply     Deaths    Houses      Houses
     S&V         1263      40,046        315
     Lambeth       98      26,107         37
                            Relative risk = 315/37 ≈ 8.5

     London     1422      256,423         59
     (-S&V, Lambeth)
Cholera deaths in south London districts during last 7 weeks of
1854 Epidemic, by water supply
                                      Deaths/
     Water       Cholera              10,000
     Supply      Deaths      Houses   Houses
     S&V           2353      40,046     573
     Lambeth        302      26,107     115


     Relative risk = 573/115 ≈ 5
Cholera deaths in south London districts during the 1854
epidemic, by water supply

     Water      Cholera               Deaths/
     Supply     Deaths     Population 10,000
     S&V         4,093     266,516       153
     Lambeth       461     173,748          26
                            Relative risk = 153/26 ≈ 5.9

     London      10,367   2,362,236         43



                                Note:
        populations supplied by water companies estimated by
                           Registrar General.
Was the Use of Houses in the Denominators
Valid?

Water                             Persons/
Supply     Population   Houses    Household
S&V        266,516      40,046      6.7
Lambeth    173,748       26,107    6.7
London    2,362,236     322,576     7.3
Cholera Deaths in South Districts of London,
Sub-district Analysis, 1849 vs. 1854


  Water             Cholera Deaths
  Supply           1849        1854
  S&V              2261         2458
  Both             3905          2547
  Lambeth          1644            89


  Here we are back to ecologic analysis
Cholera Outbreak in the Golden Square Area of London, 8/31 - 9/9, 1854.
Within 250 yards of the intersection of Cambridge and Broad Streets, there
were more than 500 fatal cases
Snow immediately suspected contamination of the water of the
much-used street pump on Broad Street near Cambridge Street.
Snow mapped the places of residence of
cholera decedents from August 31 -
September    2    in   the     broader
           neighborhood…

…and found that 73 of 83 deaths had
taken place within a short distance of the
pump.
Snow investigated the water source of the 73
decedents who lived near Broad Street pump

  • 61 -- drank water from the pump
  • 6 -- did not
  • 6 -- could get no information
10 Deaths in houses located nearer to
another street pump

 • 5 always used the Broad Street pump,
   as they preferred its water

 • 3 (children) went to school near the
   Broad Street pump
Handle of the pump was removed on
September 8

 • Legend has it that the removal of the pump handle
    caused the end of the epidemic
 • Snow himself wondered whether removing the pump
    handle had a beneficial effect
     – Epidemic was already subsiding
     – Much of the population in the neighborhood had fled


“…it is impossible to decide whether the water from the
pump still contained the cholera poison in an active state.”
Snow’s investigation of Golden Square
Outbreak: workhouse near Broad St.
 • Surrounded by houses in which deaths from cholera occurred
 • Only 5 deaths among 535 inmates
 • Workhouse had a pump-well on the premises
 • Also received water from the Grand Junction Water Works
 • Did not use Broad Street pump
 • Would have expected more than 100 deaths based on mortality in
   surrounding streets
Snow’s investigation of Golden Square
Outbreak: Brewery on Broad St.
• Located near the pump
• More than 70 workers
• None died of cholera
• Workers drank malt liquor, not water
• Deep well located in brewery
• Workers never obtained water from Broad Street Pump
Snow’s recommendations for prevention of
cholera during an epidemic
 • Observe strictest cleanliness around the sick.
 • Wash linens of patients as soon as they are removed.
 • Boil water for drinking and preparing food (unless known to
   come from clean source).

 • Wash or heat to 212°F all food.
 • Healthy should not live in same room as sick.
 • Pit-men should work 4 hour shifts, and not eat in mines.
 • Educate the people about communicability of cholera.
Snow’s recommendations for long-term
prevention of cholera
 • Effect good and perfect drainage.
 • Provide water supply free from contamination with
   contents of sewers, cesspools, house-drains, and refuse
   of people who navigate the rivers.

 • Provide model lodging-houses for the vagrant class and
   sufficient house room for the poor in general.

 • Teach habits of personal and domestic cleanliness
   among the people.

 • Screen persons arriving from infected places.
Medical establishment slow to catch on
 • 1855 report of Scientific Committee for Scientific
   Enquiries in Relation to the Cholera Epidemic of 1854:
   “…on the whole of evidence, it seems impossible to
   doubt that the influences, which determine in mass the
   geographical distribution of cholera in London, belong
   less to the water than to the air.”

 • 1856 Report on the last two cholera epidemics of London
   as affected by the consumption of impure water: “…under
   the specific influence which determines an epidemic
   period, fecalized drinking-water and fecalized air equally
   may breed and convey the poison.”
Sanitary ‘movement’ eventually succeeded in
spite of its incorrect miasma theory

 • Extensive improvements in several of London’s water
   supplies, including Southwark and Vauxhall, had already
   been ordered before the 1853-54 epidemic.

 • In next London epidemic (1866), William Farr himself
   used epidemiology to show that the source of the
   epidemic was impure water from the East London Water
   Company.
What We Know Now?
• Cholera caused by a bacterium (Vibrio cholerae;
  discovered in 1883 by Robert Koch)
• Small intestine is primary site of infection
• Diarrhea caused by cholera toxin produced by Vibrio
  cholerae
• Treatment: intravenous or oral fluid and electrolytes,
  depending on severity of illness
• Environmental reservoir for Vibrio cholerae in the sea,
  where it lives on zooplankton and shellfish
Vibrio Cholerae
200
5

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:2/29/2012
language:English
pages:112