Module 5 Case Assignment: Pertussis (Whooping Cough) Tasks Part A: In one page maximum Briefly describe the disease: Pertussis in terms of its infectivity, pathogenicity, and virulence. Identify any reservoir(s), and mode(s) of transmission Part B: (1-2 pages) Weighing the benefits and the risks, take a clear position on whether you feel vaccination programs for Pertussis (whooping cough) should be expanded in your current community.  Explain factors that went into your decision. HELPING REFERENCES U.S. Food & Drug Administration, Center for Food Safety & Applied Nutrition (n.d.) Bad Bug Book. Retrieved February 21, 2013 from http://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/default.htm FAO. Epidemiology: some basic concepts and definitions. Retrieved February 21, 2013 from http://www.fao.org/wairdocs/ILRI/x5436E/x5436e04.htm Centers for Disease Control and Prevention (2004). How to Investigate an Outbreak. Retrieved February 21, 2013 from http://www.cdc.gov/excite/classroom/outbreak/steps.htm Aschengrau A, Seage GR (2003). Chapter 6: Overview of Epidemiologic Study Designs. Essentials of Epidemiology in Public Health, Boston: Jones & Bartlett Publishers. Retrieved February 21, 2013 at: http://publichealth.jbpub.com/aschengrau/Aschengrau06.pdf Cosio G (2005). Epidemiological Overview of Tuberculosis [Presentation]. Retrieved February 21, 2013 from www.paho.org/cdmedia/dpccd01/Presentations/Day1/EPIDEMIOLOGICAL%20OVERVIEW%20OF%20TUBERCULOSIS%202.ppt Optional Readings Long SG, DuPont HL, Gaul L, Arafat RR, Selwyn BJ, Rogers J, et al. (2007). Pulsed-field gel electrophoresis for Salmonella infection surveillance, Texas, USA. Emerg Infect Dis [serial on the Internet]. Retrieved fro http://www.cdc.gov/EID/content/16/6/983.htm READ: Variations in Severity of Illness The severity of an illness may be measured by the case fatality rate or the proportion of surviving patients with complications.  The case fatality rate is defined as the number of deaths from a particular disease divided by the number of clinically apparent cases of that disease.   An infectious disease may have a wide variety of clinical symptoms, ranging from no symptoms to severe clinical illness or death.  Diseases such as tuberculosis have a high proportion of asymptomatic individuals (low pathogenicity), while diseases such as measles have a high proportion of symptomatic infections and a small percent of severe or fatal illness.  Diseases such as the African hemorrhagic fevers caused by Marburg and Ebola virus are very severe and usually fatal.  For diseases with low pathogenicity, only a small fraction of cases are often diagnosed and reported.  Control measures should be directed toward all infections capable of being transmitted to others, not just the symptomatic cases.   From a public health perspective, diseases of high incidence and lesser severity may be considered a more serious problem becaus.

1. Module 5 Case Assignment:
Pertussis (Whooping Cough)
Tasks
Part A: In one page maximum
Briefly describe the disease: Pertussis in terms of its infectivity,
pathogenicity, and virulence.
Identify any reservoir(s), and mode(s) of transmission
Part B: (1-2 pages)
Weighing the benefits and the risks, take a clear position on
whether you feel vaccination programs for Pertussis (whooping
cough) should be expanded in your current community. Explain
factors that went into your decision.
HELPING REFERENCES
U.S. Food & Drug Administration, Center for Food Safety &
Applied Nutrition (n.d.) Bad Bug Book. Retrieved February 21,
2013 from
http://www.fda.gov/Food/FoodSafety/FoodborneIllness/Foodbor
neIllnessFoodbornePathogensNaturalToxins/BadBugBook/defau
lt.htm
FAO. Epidemiology: some basic concepts and definitions.
Retrieved February 21, 2013 from
http://www.fao.org/wairdocs/ILRI/x5436E/x5436e04.htm
Centers for Disease Control and Prevention (2004). How to
Investigate an Outbreak. Retrieved February 21, 2013 from
http://www.cdc.gov/excite/classroom/outbreak/steps.htm
Aschengrau A, Seage GR (2003). Chapter 6: Overview of
Epidemiologic Study Designs. Essentials of Epidemiology in
Public Health, Boston: Jones & Bartlett Publishers. Retrieved
February 21, 2013 at:
http://publichealth.jbpub.com/aschengrau/Aschengrau06.pdf
Cosio G (2005). Epidemiological Overview of Tuberculosis
[Presentation]. Retrieved February 21, 2013 from
www.paho.org/cdmedia/dpccd01/Presentations/Day1/EPIDEMI

2. OLOGICAL%20OVERVIEW%20OF%20TUBERCULOSIS%202
.ppt
Optional Readings
Long SG, DuPont HL, Gaul L, Arafat RR, Selwyn BJ, Rogers J,
et al. (2007). Pulsed-field gel electrophoresis for
Salmonella
infection surveillance, Texas, USA. Emerg Infect Dis [serial on
the Internet]. Retrieved fro
http://www.cdc.gov/EID/content/16/6/983.htm
READ:
Variations in Severity of Illness
The severity of an illness may be measured by the case fatality
rate or the proportion of surviving patients with complications.
The
case fatality rate
is defined as the number of deaths from a particular disease
divided by the number of clinically apparent cases of that
disease.
An infectious disease may have a wide variety of clinical
symptoms, ranging from no symptoms to severe clinical illness
or death. Diseases such as tuberculosis have a high proportion
of asymptomatic individuals (low pathogenicity), while diseases
such as measles have a high proportion of symptomatic
infections and a small percent of severe or fatal illness.
Diseases such as the African hemorrhagic fevers caused by
Marburg and Ebola virus are very severe and usually fatal. For
diseases with low pathogenicity, only a small fraction of cases
are often diagnosed and reported. Control measures should be
directed toward all infections capable of being transmitted to
others, not just the symptomatic cases.
From a public health perspective, diseases of high incidence and
lesser severity may be considered a more serious problem
because it causes a large degree of mortality in the population

3. as a whole.
Components of the Infectious disease process
Many factors affect the infectious disease process. Examples of
factors which are dependent on the agent, include growth
requirements, the ability to survive outside a host, and the
ability to become resistant to antibiotics. Many factors are
dependent on the interaction between the agent and the host.
These factors include infectivity, pathogenicity, virulence, and
immunogenicity. These factors may be affected by
environmental conditions, dose, route of infection, and host
factors (e.g. age, race, and nutritional status).
Infectivity
is defined as the ability of the agent to invade and multiply
(produce infection in a host). An example of a disease with
high infectivity would be measles; a disease with low infectivity
would be leprosy. Techniques for evaluating infectivity include
speed that an agent spreads through a population and proportion
of close contacts who become infected.
Pathogenicity
, discussed earlier, is defined as the ability to produce clinically
apparent illness.
Virulence
is defined as the proportion of clinical cases resulting in
severe
clinical manifestations. The case fatality rate is commonly
used to measure virulence.
Immunogenicity
is defined as the infection's ability to produce specific
immunity. Immunogenicity can be affected by host factors such
as age, nutrition, dose, and virulence of infection.
An infectious agent may produce disease using a variety of
mechanisms. These mechanisms include direct tissue invasion,
production of a toxin, allergic reaction leading to damage in a
host, chronic infection, increased susceptibility of host to
nontoxic drugs, and immune suppression. Examples of
pathogens that produce disease by direct tissue invasion include

4. many parasitic diseases and viral infections. Pathogens that
cause illness by producing a toxin include tetanus and
Staphylococcal aureus
, which occurs in staphylococcal food poisoning. Pathogens
that have immunologic mechanisms include tuberculosis and
dengue hemorrhagic fever. Chronic infections may occur after a
clinical infection in the pharynx (e.g.
Haemophilus influenzae
), gall bladder (
Salmonella typhi
), gastrointestinal system (e.g. many species of salmonella), or
the urinary tract (e.g.
E. coli
). An agent may also increase a host's sensitivity to nontoxic
drugs (e.g. Reye's syndrome). Finally, HIV is an example of an
infectious agent that produces disease by suppressing immunity.
Reservoirs
Reservoirs
are defined as the living organisms or inanimate matter (e.g.
soil) where an infectious agent lives and multiplies. The
concept of the reservoir is important in infectious disease
because the reservoir is the component of the cycle where an
infectious agent can survive indefinitely. Humans are the main
reservoir for most of the viral and bacterial respiratory
diseases. Vertebrate animals are reservoirs for diseases such as
brucellosis (from cows, pigs, and goats), anthrax (from sheep),
leptospirosis (from rodents), and rabies (from dogs, bats, and
other animals). These diseases that are acquired from animals
are known as
zoonoses
.
Infection has occurred when infectious agent has entered and
established itself in a host. At the minimal level, the agent may
be present on surface of body and multiply at a rate sufficient to
maintain its numbers without producing identifiable reaction in
a host, which is referred as

5. colonization
(e.g.
Staphylococcal aureus
in the nasal passage). At the next level, organisms multiply
and cause a measurable reaction that is not clinically detectable,
which is referred to as
inapparent infection
. The final level is when infection leads to clinical disease. All
are potential sources of infection to others.
A
carrier
is defined as an infected person who does not have apparent
clinical disease, but is a potential source of infection to others.
Carriers include individuals who are asymptomatic throughout
their infection, as well as those who are carriers during the
incubation period or who become carriers after their symptoms
subside. When the carrier state persists for a long time, the
person is referred to as a
chronic carrier
.
Mechanism of Disease Transmission
The method by which which an infectious agent escapes a
reservoir and enters a host is referred to as
mechanism of transmission
. There are two main types of transmission: direct transmission
and indirect transmission. In
direct transmission
, an infectious agent is immediately transferred from one
infected host or reservoir to another. Direct transmission
includes not only direct contact, such as kissing, but also spray
by droplets through sneezing and coughing onto the mucous
membranes of others. Droplet spread is classified as direct
transmission because it occurs over short distances--the droplets
travel a few feet before falling to the ground.
There are three types of indirect transmission: vehicleborne,
vectorborne, and airborne.

6. Vehicleborne transmission
is indirect contact through inanimate objects, such as bedding,
toys, surgical instruments, and contaminated food. In
vectorborne transmission
, the infectious agent is transmitted by an intermediary (usually
an insect) to a susceptible host. In
airborne transmission
, two types of particles may be spread through the air--dusts and
droplet nuclei. Dusts are particles of varying size that result
from resuspension of particles that have settled on floors or
bedding as well as particles blown by the wind.
Coccidioidomycosis is an example of a disease that is spread by
airborne transmission of fungal spores. Droplet nuclei are very
tiny particles that may be suspended in the air for long periods
of time. They represent the dried residue of droplets from
coughing, sneezing, or the aerosolization of infective materials.
Control Measures
Control measures may be categorized as those directed against
the reservoir, those that interrupt transmission, and those that
reduce the susceptibility of the host. When the reservoir
involves a domestic animal, control measures may involve
immunization, testing of herds, and destruction of infected
animals. Control measures targeted towards human reservoirs
include isolation of infected persons, temporary removal of
individuals from sensitive occupations (e.g. foodhandlers with
diarrheal illness), treatment to make them non-infectious, health
education regarding hygiene, and disinfection of contaminated
objects.
Isolation
refers to the separation of infected persons from those not
infected for the period that they are infectious. Another control
measure, related to isolation is
quarantine
, which is the limitation of the freedom of movement of
apparently well persons or animals who have been exposed to a
case of infectious disease. Control measures that interrupt the

7. transmission of organisms include environmental measures,
such as water purification and pasteurization of milk. Control
measures that reduce host susceptibility include active
immunization, which causes a host to produce antibodies, and
passive immunization. An example of active immunization is
DTP (immunization against diptheria, tetanus, and pertussis).
An example of passive immunization includes the
administration of immune serum globulin to prevent hepatitis A.
Sources;
U.S. Department of Health and Human Services CDC (2007)
Principles of Epidemiology in Public Health Practice. Third
Edition. Retrieved on September 2, 2011 from
http://www.cdc.gov/training/products/ss1000/ss1000-ol.pdf
Rockett I. Population and health: An introduction to
Epidemiology. Second Edition Vol 54, No 4. (2002) PAHO.
Retireved September 2, 2011 from:
http://www.prb.org/Source/54.4PopHealthEpidemiology.pdf