Communicable Disease


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.

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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.

Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.

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Epidemiological Triad

 

 

Host

 

 

Agent

 

 

Environment

 

 

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

Infectious agent has invaded a host and found conditions hospitable to replicate

Replication before shedding

Communicable period

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.

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Stages of Infection (Cont.)

Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.

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Figure 25-1 From Grimes DE: Infectious diseases, St Louis, 1991, Mosby.

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.

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Chain of Transmission (Cont.)

Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.

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Figure 25-2

Chain of Transmission: Part 1

Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.

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Table 25-1

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

 

 

 

 

Chain of Transmission: Part 2

Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.

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Table 25-1

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

 

 

 

 

Breaking the Chain of Transmission

Controlling the agent

Eradicating the nonhuman reservoir

Controlling the human reservoir

Quarantine—during incubation period

Controlling the portals of exit and entry

Isolation of sick persons

Universal precautions

Improving host resistance and immunity

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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

Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc.

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Table 25-2

 

Type

 

 

 

How Acquired

 

Length of Resistance

 

Natural

 

 

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

 

 

Artificial

 

 

Active

 

 

Inoculation of antigen

 

 

May be temporary or permanent

 

 

Passive

 

 

Inoculation of antibody or antitoxin

 

 

Temporary

 

 

 

 

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

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Figure 25-3

 

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

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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)

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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.

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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.

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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.

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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.

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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.

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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.

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Prevention of Communicable Diseases

Primary prevention

To prevent transmission of an infectious agent and to prevent pathology in the person exposed to an infection

Secondary prevention

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

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