Epidemiology - University of South...

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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

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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?


Investigative Follow Up


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

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Common Source Outbreak -

Cryptosporidium


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


Propagated Outbreak -

Measles


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.


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

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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


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.


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.

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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.

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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


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)

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• 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



Community-Acquired

• If the patient enters

the hospital with

apparent signs and

symptoms the

disease is considered

community-acquired

(community-

associated)

• MRSA


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

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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


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


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


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


Cause of the Outbreak

• Dr. John Snow

mapped the cases of

cholera and

interviewed survivors -

determined link to

broad street pump.


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.

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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.


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.


Notifiable Diseases in US, 2008

Reproduced from CDC, Summary of Notifiable Diseases, 2008.


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

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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


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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)


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

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WHO’s

innovative

approach to

global disease

surveillance

Adapted from Grein, T.W., et al., Emerging

Infectious Diseases 6 (2000): 97-102.


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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


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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


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)


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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

Epidemiology - University of South...

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