Communicable Disease and Infectious Disease.
According to the World Health Orgnization, an
emerging
infectious disease (EID) is an infectious disease that has appeared in a population for the first time, or that may have existed previously but is rapidly increasing in incidence or geographic range (
WHO
). Outbreaks are the occurrence of disease cases in excess of what would normally be expected for a community, geographical area or season (WHO). Examples of recent outbreaks affecting public health in United States include
Group A Streptococcus
,
Pertussis
,
Zika,
Mumps
, and
Measles
.
Read chapter 25 of the class textbook and review the attached PowerPoint presentation. Once done answer the following questions;
Chapter 25
Communicable Disease
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
Principles of Infection and Infectious
Disease Occurrence
Biological and epidemiological principles
➢
Multicausation
➢ Spectrum of Infection
➢ Stages of Infection
➢ Spectrum of disease occurrence
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
2
Multicausation
Disease etiology is
complex and
multicausal.
An infectious agent
alone is not sufficient
to cause disease; the
agent must be
transmitted within a
conducive environment
to a susceptible host.
Host
Environment
Agent
Epidemiological Triad
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Spectrum of Infection
Not all contact with an infectious agent leads
to infection, and not all infection leads to an
infectious disease.
➢
➢
➢
➢
Subclinical infection: no overt symptomatic
disease (unapparent or asymptomatic)
Infections: entry and multiplication of infectious
agent in host
Infectious disease and communicable disease:
pathophysiological responses of the host to the
infectious agent, manifesting as an illness
(considered a case)
Carriers: people who continue to shed infectious
agent without any symptoms of disease
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Stages of Infection
Latent period
➢
➢
Communicable period
➢
➢
Infectious agent has invaded a host and found conditions
hospitable to replicate
Replication before shedding
Follows latency
Begins with shedding of agent
Incubation period
➢
➢
Time from invasion to time when disease symptoms first
appear
May overlap with communicable period
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
5
Stages of Infection (Cont.)
Figure 25-1 From Grimes DE: Infectious diseases, St Louis, 1991, Mosby.
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
6
Spectrum of Disease Occurrence
Incidence—new cases in a population
Endemic—diseases that occur at a consistent,
expected level in a geographic area
Outbreak—an unexpected occurrence of an
infectious disease in a limited geographic area during
a limited period of time
Epidemic—an unexpected increase of an infectious
disease in a geographic area over an extended
period of time
Pandemic—steady occurrence of a disease over a
large geographic area or worldwide
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Chain of Transmission
Infectious agents
Reservoirs
Portals of exit and entry
Modes of transmission
➢
Direct
➢ Indirect
• Fomites or vectors
➢ Fecal-oral, airborne
Host susceptibility
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
8
Chain of Transmission (Cont.)
Figure 25-2
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Chain of Transmission: Part 1
Links
of the Chain
Definition
Factors
Infectious agent
An organism (virus,
rickettsia, bacteria,
fungus, protozoan,
helminth, or prion)
capable of producing
infection or infectious
disease
Properties of the agent:
morphology, chemical
composition, growth
requirements, and viability.
Interaction with the host: mode
of action, infectivity,
pathogenicity, virulence,
toxigenicity, antigenicity, and
ability to adapt to the host
Reservoirs
The environment in
which a pathogen lives
and multiplies
Humans, animals, arthropods,
plants, soil, or any other organic
substance
Portal of exit
Means by which an
infectious agent is
transported from the host
Respiratory secretions, vaginal
secretions, semen, saliva, lesion
exudates, blood, and feces
Table 25-1
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Chain of Transmission: Part 2
Links
of the Chain
Definition
Factors
Mode of
transmission
Method whereby the
infectious agent is
transmitted from one
host (or reservoir) to
another host
Direct: person to person
Indirect: implies a vehicle of
transmission (biological or
mechanical vector, common
vehicles or fomite)
Airborne droplets
Portal of entry
Means by which an
infectious agent enters a
new host
Respiratory passages, mucous
membranes, skin, percutaneous
injection, ingestion, and through
the placenta
Host susceptibility
The presence or lack of
sufficient resistance to an
infectious agent to avoid or
prevent contracting an
infection or acquiring an
infectious disease
Biological and personal
characteristics (e.g., gender,
age, genetics), general health
status, personal behaviors,
anatomical and physiological
lines of defense, immunity
Table 25-1
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Breaking the Chain of Transmission
Controlling the agent
Eradicating the nonhuman reservoir
Controlling the human reservoir
➢
Controlling the portals of exit and entry
➢
➢
Quarantine—during incubation period
Isolation of sick persons
Universal precautions
Improving host resistance and
immunity
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Types of Immunity
Natural immunity: an innate resistance to a specific
antigen or toxin
Acquired immunity: derived from actual exposure to
specific infectious agent, toxin, or appropriate vaccine
➢
➢
Active acquired: body produces its own antibodies
Passive acquired: temporary resistance that has been
donated to the host
Primary vaccine failure: failure of vaccine to stimulate
any immune response
Secondary vaccine failure: waning of immunity
following an initial immune response
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Types of Acquired Immunity
Type
Natural
How Acquired
Length of
Resistance
Active
Natural contact and
infection with the antigen
May be temporary
or permanent
Passive
Natural contact with
antibody transplacentally
or through colostrum and
breast milk
Temporary
Active
Inoculation of antigen
May be temporary
or permanent
Passive
Inoculation of antibody or
antitoxin
Temporary
Artificial
Table 25-2
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
14
Types of Immunity
Herd immunity: a state in which those not immune to
an infectious agent will be protected if a certain
proportion (generally considered to be 80%) of the
population has been vaccinated or is otherwise
immune
Figure 25-3
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
15
Public Health Control of Infectious
Diseases
Control
➢
The reduction of incidence (new cases) or prevalence (existing
cases) of a given disease to a locally acceptable level as a result of
deliberate efforts
Elimination
➢
Controlling a disease within a specified geographic area and
reducing the prevalence and incidence to near zero
➢ The result of deliberate efforts, but continued intervention measures
are required
Eradication
➢
Reducing the worldwide incidence of a disease to zero as a
function of deliberate efforts (e.g., smallpox in 1977)
➢ No need for further control measures
➢ Only possible under certain conditions
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Criteria for Disease Eradication
Human host only; no host in nature
Easy diagnosis; obvious clinical manifestations
Limited duration and intensity of infection
Natural lifelong immunity after infection
Highly seasonal transmission
Availability of vaccine, curative treatment, or both
Substantial global morbidity and mortality rates
Cost effectiveness of campaign and eradication
Integration of eradication with additional public health
variables
Eradication imperative over control measures
– CDC (1993)
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
17
Notifiable Infectious Diseases in the
United States
HCP MUST report to local or regional health
departments → state health dept. →CDC
Reported weekly in the MMWR
Go to CDC website for latest listing of
diseases: http://www.cdc.gov
Note: State health departments have the responsibility for
monitoring and controlling communicable diseases within their
respective states; they determine which diseases will be reported
within their jurisdiction. Those lists might be longer than the CDC’s
list.
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Vaccines and Infectious Disease
Prevention
Immunization is a broad term used to
describe a process by which active or passive
immunity to an infectious disease is induced
or amplified.
➢
Immunizing agents can include vaccines as well
as immune globulins or antitoxins.
Vaccination is a narrower term referring to the
administration of a vaccine or toxoid to confer
active immunity by stimulating the body to
produce its own antibodies.
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
19
Recommended Immunization
Schedules
Recommendations for international
immunization practices determined by WHO
In the United States, AAP and ACIP
Current U.S. recommendations found on
CDC website: http://www.cdc.gov/vaccines
Schedules, footnotes, and educational fact
sheets provide guidelines for practice
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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Vaccines: Words of Caution
Information and recommendations on
immunizations and vaccine usage change
regularly
Vaccine Information Statements (VISs)
that explain the benefits and risks must be
given out before vaccine is administered—
a federal law!!
(http://www.cdc.gov/vaccines/hcp/vis/index.html)
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
21
Available Vaccines by Type
Live attenuated vaccines (See Textbook Table
25-3)
Viral: measles, mumps, rubella, oral polio,
vaccinia, yellow fever, varicella
Bacterial: BCG (Bacille Calmette-Guérin)
Recombinant: oral typhoid
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
22
Available Vaccines by Type (Cont.)
Inactivated vaccines (See Textbook Table 25-3)
Viral: influenza, polio, rabies, and hepatitis A
Bacterial: typhoid, cholera, and plague
Subunit (fractional): influenza, acellular pertussis,
typhoid Vi and Lyme disease
Toxoid: diphtheria and tetanus
Recombinant: hepatitis B
Conjugate polysaccharide: Haemophilus influenzae
type B and pneumococcal 7-valent
Pure polysaccharide: Pneumococcal 23-valent,
meningococcal, and Haemophilus influenzae type b
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
23
Recommended Vaccine Schedules
(Textbook Box 25-6)
Children/adolescents
➢ http://www.cdc.gov/vaccines/schedules/hcp/child-adolescent.html
Adults
➢ http://www.cdc.gov/vaccines/schedules/hcp/adult.html
Travelers
➢ http://wwwnc.cdc.gov/travel/destinations/list
Pregnant women
➢ www.cdc.gov/vaccines/pubs/preg-guide.htm
Health care workers
➢ www.cdc.gov/vaccines/spec-grps/hcw.htm
Specific health conditions
➢ www.cdc.gov/vaccines/spec-grps/conditions.htm
Other special groups
➢ www.cdc.gov/vaccines/spec-grps/default.htm
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
24
Vaccine Storage, Transport,
and Handling
Cold chain
Routes of administration, dosage, and
sites
Proper timing and spacing
Hypersensitivity and contraindications
Documentation
Vaccine safety and reporting of adverse
events and vaccine-related injuries
(VAERS)
Vaccine needs for special groups
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
25
Prevention of Communicable
Diseases
Primary prevention
➢
Secondary prevention
➢
To prevent transmission of an infectious agent and
to prevent pathology in the person exposed to an
infection
Activities to detect early and effectively treat
persons who are infected
Tertiary prevention
➢
Caring for persons with an infectious disease to
ensure that they are cured or that their quality of
life is maintained
Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.
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