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
3
For the state!
AIDS
SNHD Reportable Diseases
Amebiasis
Animal bite from a rabies susceptible species
Anthrax
Botulism
Brucellosis
Campylobacteriosis
Chancroid
Chlamydia
Cholera
Coccidioidomycosis
Cryptosporidiosis
Dengue
Diphtheria
E. coli 0157:H7
Encephalitis
Extraordinary occurrence of illness
Foodborne disease outbreak
Giardiasis
Gonorrhea
Granuloma Inguinale
Haemophilus Influenzae (invasive)
Hansen's Disease (leprosy)
Hantavirus
Hemolytic-uremic syncrome (HUS)
Hepatitis A, B, C, delta, unspecified
HIV infection
Influenza
Legionellosis
Leptospirosis
Listerosis
Lyme Disease
Lymphogranuloma Venereum
Malaria
Measles (rubeola)
Meningitis (specify type)
Meningococcal disease
Mumps
Pertussis
Plague
Poliomyelitis
Psittacosis
Q Fever
Rabies (human or animal)
Relapsing Fever
Respiratory Syncytial Virus (RSV) 4
Rocky Mountain Spotted Fever
Southern Nevada
Rotavirus
Health District
Rubella
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
HIV/AIDS
Phone
(702) 759-0702
Fax
(702) 868-2825
Sexually Transmitted Diseases
Tuberculosis
Other Reportable Diseases
Foodborne Illness Outbreaks
(702) 759-0705
(702) 759-1369
(702) 759-1300
(702) 759-1300
(702) 383-1446
(702) 633-0975
(702) 383-4936
(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
• 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
13
Selling Soap
By STEPHEN J. DUBNER and STEVEN D. LEVITT
The New York Times
September 24, 2006
“In one Australian medical study, doctors selfreported 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
– Family cook
• Typhoid fever
bacteriologist
Emma Sherman
Mary Mallon
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
infectious agent
during the
incubation period
Recuperating but
continue to shed
infectious agent
Remains
infected
for a long
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
52