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Emerging Infectious DiseasesHSC4933
Epidemiology
of Infectious Diseases
Presented by Christy Ottendorfer, PhD, MSPH
"A man should look for what is, and not for
what he thinks should be."
- Albert Einstein
HSC4933. Emerging Infectious Diseases 2
Learning Objectives
• Define epidemiology and types of disease occurrence (endemic, sporadic, etc)
• Distinguish common source from propagated outbreaks
• Define important disease measures (prevalence, etc) & disease reservoirs
• Describe the purpose and list the steps of an outbreak investigation
• Identify control and prevention methods
• Identify control measures at local, national and international agencies
3
Concepts of Epidemiology
• Epidemiology is an investigative
branch of medicine that deals
with the source, cause, and
possible control of infectious
disease and other public health
problems
• Epidemiologists are challenged
to determine why an outbreak of
disease occurs at a particular time
and/or particular place
©2010 Jones & Bartlett Publishers, LLC HSC4933. Emerging Infectious Diseases 4
Epidemiology
• Study of disease
occurring
within populations:– Who is getting the disease?
– Where is it occurring?
– When is it occurring?
– Are there common
factors among all
of the people who
have the disease?
HSC4933. Emerging Infectious Diseases 5
Investigative Follow Up
HSC4933. Emerging Infectious Diseases 6
Common Source Outbreaks
• When a large number of
cases occur following a
shared exposure
• Implies a common source for
the occurrence of the disease
– Foodborne outbreak
– Waterborne outbreak
• Number of cases peaks
sharply
2
HSC4933. Emerging Infectious Diseases 7
Common Source Outbreak -
Cryptosporidium
HSC4933. Emerging Infectious Diseases 8
Propagated Epidemics
• Occur when infected individuals
transmit a disease to a new susceptible
host (person-to-person)
• There is a gradual increase in the # of
cases
– Measles
– Meningitis
HSC4933. Emerging Infectious Diseases 9
Propagated Outbreak -
Measles
HSC4933. Emerging Infectious Diseases 10
Epidemic
• An unusually large
number of cases of
a particular disease
occurring in a
community within a
short time.
• Annual influenza
epidemics occur
each winter in the
U.S.
HSC4933. Emerging Infectious Diseases 11
Pandemic
• Occurs when an
epidemic spreads
throughout many
parts of the world.
• The influenza
pandemic of 1918-
1919 is the most
famous and most
deadly epidemic,
followed by Black
Death (plague). HSC4933. Emerging Infectious Diseases 12
Endemic and Sporadic
• Endemic = a limited number of cases of
an infectious disease is present at all
times within a geographic area.
– Strep throat (Streptococcus pyogenes)
• Sporadic = a particular disease occurs
without regularity in a community.
– West Nile Encephalitis
3
HSC4933. Emerging Infectious Diseases 13
Disease Statistics
• Can be described
using a number of
variables but most
common are:
– prevalence
– incidence
– morbidity
– mortality
Source: MI Dept. of AgricultureHSC4933. Emerging Infectious Diseases 14
Prevalence
• Refers to the total
number of cases of a
particular disease at a
given point in time.
• Often used to describe
chronic diseases such
as cancer and diabetes.
• A change in prevalence
can effect public health
programs.HIV prevalence S. Africa
HSC4933. Emerging Infectious Diseases 15
Incidence
• The rate of NEW
cases that occur
within a specified
time INTERVAL.
• Often used to
describe infectious
diseases.
• Also can be used to
initiate public health
intervention.
HSC4933. Emerging Infectious Diseases 16
Morbidity and Mortality
• Morbidity is a term
used to describe
illness.
– Can be expressed in
terms of loss of quality
of life, loss of work,
etc.
– Many diseases are not
fatal but have
profound effects on a
person’s life.
• Mortality is death.
• CFR or case fatality
rate refers to the
number of deaths that
result from infection
with a particular
disease.
17
Natural ReservoirsReservoir is a site where microbes survive (&
may multiply) and get transmitted • All pathogens, to exist, must
have one or more reservoirs• Prime targets for preventing,
minimizing, and eliminating existing and potential epidemics – Humans are the only known
reservoir for smallpox, gonorrhea, measles, polio, etc.
– Zoonoses are diseases in which animals serve as reservoirs
©2010 Jones & Bartlett Publishers, LLC HSC4933. Emerging Infectious Diseases 18
Disease Carrier States
• Active carrier = person
has disease + symptoms
• Healthy carrier = person
harbors the infectious
agent but NO symptoms
– Transient = sheds
pathogen for several days
or months
– Chronic = can transmit
infectious agent for
months or years.
4
19
Nonliving Reservoirs
Some organisms are able to survive
and multiply in nonliving environments, such as
soil and water
• Spore formers, like the clostridia (cause of tetanus
and botulism) can survive for many years in soil
©2010 Jones & Bartlett Publishers, LLC 20
Transmission
Transmission is the mechanism by
which an infectious agent is spread
to a susceptible person
©2010 Jones & Bartlett Publishers, LLC
HSC4933. Emerging Infectious Diseases 21
Hospital-Acquired
• Refers to an infectious
disease that is contracted
by a person during a
hospital stay.
• Also known as hospital-
associated and
nosocomial.
• MRSA (methicillin-
resistant Staphylococcus
aureus)
22
• Hospital environment as a source of the problem
– Foster development of antibiotic resistant strains of
bacteria
– Invasive procedures and insertion of needles,
catheters, tubes facilitate the direct transmission of
microbes
– Many patients are ill and may have weakened immune
system
Nosocomial Infections & Hospitals
©2010 Jones & Bartlett Publishers, LLC
HSC4933. Emerging Infectious Diseases 23
Community-Acquired
• If the patient enters
the hospital with
apparent signs and
symptoms the
disease is considered
community-acquired
(community-
associated)
• MRSA
HSC4933. Emerging Infectious Diseases 24
Outbreak
Definition:
1) a sudden or violent increase in activity or currency <the outbreak of war>
2) a sudden rise in the incidence of a disease<an outbreak of measles>
3) a sudden increase in numbers of a harmful organism and especially an insect within a particular area <an outbreak of locusts>
Source: Merriam-Webster Online Dictionary
5
HSC4933. Emerging Infectious Diseases 25
What, where, when, who?
3 main objectives of outbreak investigation:
1. Identify responsible etiologic agent (what?)
2.Find source of infectionby studying occurrence of the disease among persons (who?) or in a place (where?) or time (when?), as well as determining specific attack rates
3. Develop recommendations to prevent further transmission
HSC4933. Emerging Infectious Diseases 26
8 Steps in Outbreak Investigation
• Confirm existence of outbreak
• Verify diagnosis or detection of disease
• Establish case definition
• Identify case counts,
date of onset, symptoms,
risk factors present?
• Identify all characteristics
of time, place, person (maps)
• Hypothesize
• Control & Prevention
• Report findings
HSC4933. Emerging Infectious Diseases 27
Cholera Disease Definition
• Symptoms of disease
include profuse watery
diarrhea, vomiting, and leg
cramps.
• Fluid loss can reach 1 liter
• Diarrhea characteristically
rice water in appearance.
• Death can occur rapidly
due to massive fluid
loss/electrolyte imbalance.
Source: Doctors without Borders
HSC4933. Emerging Infectious Diseases 28
Outbreak - Cholera 1854
England• An outbreak of cholera occurred in the Soho
area of London in 1849.
• A estimated total of 616 people
– 100s in the first days of the outbreak.
• Cause of death thought to be “miasma” or bad
air
• Public health authorities attributed the deaths to
poor air quality despite facts against this theory:
– those working in very poor air were not sick
– cases were occurring in a defined area of the city
HSC4933. Emerging Infectious Diseases 29
Cause of the Outbreak
• Dr. John Snow
mapped the cases of
cholera and
interviewed survivors -
determined link to
broad street pump.
HSC4933. Emerging Infectious Diseases 30
Public Health Intervention –
The Famous Pump Handle
• Clergyman Henry Whitehead
discovered the index case
leading to the route of infection.
• Index case lived @ 40 Broad
Street and excavation of this
residence found a cesspool
(located 2 feet and 8 inches
from the well) connected to
the Broad Street Pump.
• John Snow removed the handle of the pump.
6
HSC4933. Emerging Infectious Diseases 31
Ending the Outbreak
• Following the “proof”
that cholera is
waterborne, new
systems of sewage
and water distribution
essentially put an end
to cholera outbreaks
in London.
HSC4933. Emerging Infectious Diseases 32H1N1 Flu Map (2145 cases).
As of 05/07/09.
HSC4933. Emerging Infectious Diseases 33
Clinical Features/Case Definition
• Incubation period
• Symptoms
• Clinical & laboratory
tests (e.g. chest x-ray,
blood work)
• Laboratory confirmation
of pathogen
• Patient history (travel,
close contact with other
ill people, etc)Timeline for identification of the disease and confirmation
by public health lab that the case is part of an outbreak.
HSC4933. Emerging Infectious Diseases 34
Notifiable Diseases in US, 2008
Reproduced from CDC, Summary of Notifiable Diseases, 2008.
HSC4933. Emerging Infectious Diseases 35
Control & Prevention
• Control source of pathogen– Remove source of contamination
– Remove persons from exposure
– Inactivate or neutralize pathogen
– &/or Treat infected persons
• Prevention = interrupt transmission– Sterilize environmental sources of
transmission
– Control mosquito or vector transmission
– Improve personal sanitation
– Control or modify host response to exposure Immunize susceptible hosts
Use prophylactic drugs
Modify behavior or use barriers
36
Control At the Local Level
Community, City, and State Health Departments
• Every state has a department of health, its purpose is
– To prevent disease and promote health and safety
– To establish and implement food and water safety standards
• Restaurant inspectors enforce use of disp. gloves;
proper temperatures for cooking and storing foods; the
absence of mice, rats, roaches; & practice of appropriate
measures of sanitation and hygiene by food workers
• Food workers are also required to submit stool
specimens to avoid a repeat of “Typhoid Mary”
• Recommended to notify the CDC of selected “notifiable”
diseases
©2010 Jones & Bartlett Publishers, LLC
7
37
Control At the National Level Centers for Disease Control and Prevention, in Atlanta, GA
• Premier public health facility in United States; has global
impact
• Founded in 1946 and functions to:
– Detect and investigate health problems
– Conduct research to enhance prevention
– Develop and advocate sound public health policies
– Implement prevention strategies
– Promote healthy behaviors
– Foster safe and healthful
environments
– Provide leadership and
training (http://www.cdc.gov)
©2010 Jones & Bartlett Publishers, LLC 38
Control At the International Level
The World Health Organization (WHO)
• Headquarters in Geneva, Switzerland; 193 member
nations
• Uses sophisticated systems of surveillance and
communication to keep track of microbial diseases on a
global level
– Rapid verification and response
to epidemic outbreaks
– Influenza surveillance network;
identifies strains to include
in annual vaccine
– Combats rabies, malaria, leprosy,
sleeping sickness, filariasis,
guinea worm disease, etc. ©2010 Jones & Bartlett Publishers, LLC
39
WHO’s
innovative
approach to
global disease
surveillance
Adapted from Grein, T.W., et al., Emerging
Infectious Diseases 6 (2000): 97-102.
©2010 Jones & Bartlett Publishers, LLC
40
Ultimate Goals
• “The attainment for all people of the
world by the year 2000 of a level of
health that will permit them to lead a
socially & economically productive
life.”
• Has there been progress toward the
attainment of the goals of Alma-Alta?
– Life expectancy has dramatically
increased since the start of the 20th
century
– The only disease eradicated has been
smallpox
Courtesy of Jean Roy/CDC
Smallpox
©2010 Jones & Bartlett Publishers, LLC
41
ITFDE• Targeted six
infectious diseases for
eradication
– mumps, polio,
rubella, guinea
worm disease,
lymphatic filariasis,
and cysticercosis
– And, now measles!
• Eradication is defined
as “reduction of the
worldwide incidence
of a disease to zero”Adapted from CDC, Morbidity and Mortality Weekly Report 42 (1993): 1-25
©2010 Jones & Bartlett Publishers, LLC 42
Partnerships: The Way to Go• Partnerships are the key to preventing and coping with
epidemics and pandemics and in responding to natural
disasters quickly
• Many examples of successful local, national, and international
partnerships of private and public sectors exist:
– The earthquake in India (2001)
– SARS epidemic in China (2003)
– Tsunami in Indonesia (2004)
– Ebola outbreak in central Congo (2005)
– Hurricane Katrina in the U.S. (2006)
– Cholera outbreak in Zimbabwe (2008)
©2010 Jones & Bartlett Publishers, LLC
8
HSC4933. Emerging Infectious Diseases 43
Summary
• Epidemiology is the study of diseases in populations of humans or other animals, specifically how, when and where they occur
• Reservoirs are often associated with diseases & can be targeted for public health interventions
• Important measures of disease occurrence include endemic, pandemic, sporadic
• Key statistics (prevalence, incidence, morbidity, CFR) are often used to describe the severity and burden of a particular disease
• Outbreak investigations are used to identify the pathogen, find its source & control/prevent additional infections using a variety of public health interventions
• Local, national and international health agencies contribute to infectious disease control, research