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Definition of Terms:
 Infectious Disease:
An illness due to a specific infectious agent that is spread from an
infected person, animal, or inanimate reservoir to a susceptible host, either
directly or indirectly, through an intermediate plant or animal host, vector, or
the inanimate environment.
Infectious diseases are caused by pathogenic microorganisms, such as bacteria,
viruses, parasites or fungi; the diseases can be spread, directly or indirectly, from
one person to another.
Infectious disease: a disease caused by a microorganism and therefore potentially
infinitely transferable to new individuals. May or may not be communicable.
Example of non communicable is disease caused by toxins from food poisoning or
infection caused by toxins in the environment, such as tetanus.
Communicable disease: an infectious disease that is contagious and which can be
transmitted from one source to another by infectious bacteria or viral organisms.
Contagious disease: a very communicable disease capable of spreading rapidly
from one person to another by contact or close proximity.
When someone is known to be ill with a contagious disease, they are placed in
isolation and receive special care, with precautions taken to protect uninfected
people from exposure to the disease.
Zoonotic diseases are infectious diseases of animals that can cause disease when
transmitted to humans.
Knowledge of communicable diseases is fundamental to the practice of community
health nursing because these diseases typically spread through communities of
 Understanding of the basic concepts of communicable disease control, as
well as the numerous issues arising in this area, helps a community health
nurse work effectively to prevent and control communicable disease in
populations and groups.
 It also helps nurses teach important and effective preventive measures to
community members, advocate for those affected, and protect the well-being
of uninfected persons (including the nurses themselves).
Despite significant declines in mortality, communicable diseases are responsible
for persistently high morbidity among various age and population groups.
 Rates of some communicable diseases, especially tuberculosis (TB) and
sexually transmitted diseases (STDs), remain disproportionately high in
selected population groups
 New fears of terrorist attacks using anthrax, botulilinum (botulism), and
smallpox create areas in which community health nurses must play a role.
They can educate the public and help reduce fears and vulnerability as they
remain knowledgeable regarding infrequently seen communicable diseases
that might be potential terrorist weapons. New fears of terrorist attacks using
anthrax, botulilinum (botulism), and smallpox create areas in which
community health nurses must play a role. They can educate the public and
help reduce fears and vulnerability as they remain knowledgeable regarding
infrequently seen communicable diseases that might be potential terrorist
Global Trends
During the last several decades, substantial progress has been made in controlling
some major infectious diseases around the world, although other diseases have not
been managed as well. The following are some of the major accomplishments:
• The WHO’s Expanded Program on Immunization (EPI) was launched in 1974.
As a result, by 1995, more than 80% of the world’s children had been immunized
against diphtheria, tetanus, whooping cough, poliomyelitis, measles, and TB,
compared with fewer than 5% in 1974 (WHO, 1998).
• Global eradication of smallpox was achieved in 1980.
• In 1988, a campaign for global eradication of poliomyelitis by the year 2000 was
launched. However, polio remains endemic in 10 countries: India, Pakistan, and
Nigeria are major reservoirs, cases are also reported from Afghanistan, Niger,
Somalia, Egypt, Angola, Ethiopia, and Sudan (“Polio at All-time Low,” June/July
Some major problem communicable diseases and areas remain, including the
• Malaria remains a major threat, even though the mortality rate has improved in
the last 25 years. In 1954, there were 2.5 million deaths annually and 250 million
cases of malaria worldwide; in 2002, there were an estimated 1.5 to 2.7 million
deaths and 300 to 500 million cases. Tropical Africa has 90% of the cases, and
malaria is endemic in 92 countries. The Pan American Health Organization
Global Strategy for Malaria Control is to collaborate with affected countries to
reduce the incidence of the disease.
• Cholera was mainly confined to Asia in the early 20 th century through
improvements in sanitation elsewhere.
However, a series of pandemics have affected much of the world since 1960 and
have become more widespread and more frequent in Africa since the 1970s. A new
strain, Vibrio cholerae O139, was identified in India in 1992.
Cholera is endemic in 80 countries and is of concern in all parts of the world.
Along with other diarrheal diseases, it ranked as the third leading cause of death
worldwide in 1999, mostly among children younger than 5 years of age
(Gannon, 2000).
• TB has made a powerful resurgence in the last 3 decades as many countries let
their control programs become complacent. WHO declared TB a global emergency
in 1993. One third of the incidence in the last 5 years can be attributed to human
immunodeficiency virus (HIV) infection.
Drug-resistant strains of the TB bacillus have infected up to 50 million people
worldwide. Each year, 8million people develop TB, and 1.8 million die of the
Global successes and failures to control communicable diseases are affected by a
bevy of factors.
First, the geopolitical nature of an area influences who can respond when a
communicable disease occurs in a country.
Second, the natural and manmade resources of an area influence the health status
of the population before a disease strikes, contributing to both disease resistance
and the ability to survive once a communicable disease is contracted. This is one
reason that poorer nations have higher incidences and greater numbers of deaths
from communicable diseases.
Finally, weather and climatic factors can influence health and illness. For
example, both droughts and floods can lead to crop failure and subsequent famine.
Other such factors include hurricanes, monsoons, earthquakes, tornadoes, floods,
and fire.
Microbes That Cause Infectious Diseases (agent of infectious diseases)
 Bacteria. These one-cell organisms are responsible for illnesses such as
strep throat, urinary tract infections and tuberculosis.
 Viruses. Even smaller than bacteria, viruses cause a multitude of diseases —
ranging from the common cold to AIDS.
 Fungi. Many skin diseases, such as ringworm or athlete's foot, are caused by
fungi. Other types of fungi can infect your lungs or nervous system.
 Parasites. Malaria is caused by a tiny parasite that is transmitted by a
mosquito bite. Other parasites may be transmitted to humans from animal
 Helminths
 Prions
Modes of Transmission
The reservoir of infection can be a person, animal, insect, or inanimate material in
which the infectious agent lives and multiplies and which serves as a source of
infection to others
Direct Transmission
Direct transmission occurs by immediate transfer of infectious agents from a
reservoir to a new host. It requires direct contact with the source, through touching,
biting, kissing, or sexual intercourse, or by the direct projection of droplet spray
onto the conjunctiva or onto the mucous membranes of the eye, nose, or mouth
during sneezing, coughing, spitting, laughing, singing, or talking. Direct
transmission is limited to a distance of 1 meter or less
Indirect Transmission
Indirect transmission occurs when the infectious agent is transported within
contaminated inanimate materials such as air, water, or food. It is also commonly
referred to as vehicle borne transmission.
People may be affected by certain communicable diseases merely through carrying
on the normal activities of eating food and drinking beverages.
Food borne illnesses frequently reported
in the last few years include
salmonellosis;a bacterial agent, hepatitis A; a viral agent, and
shigellosis, a bacterial agent.
waterborne illness The most commonly reported waterborne illness is infection
by Giardia lamblia, a protozoan.
Giardia can also occur as a food contaminant. Most of the disease-causing agents
typically found in foods also survive in water to cause disease, although water may
provide a less nutritive environment and result in lower concentrations of the
agent. Most commonly, exposure to infectious food or water results in symptoms
related to gastrointestinal function, including diarrhea, nausea, vomiting, stomach
cramps, and jaundice. .
This time interval between exposure and onset of symptoms is called the
incubation period. Note that waterborne pathogens affect not only the
gastrointestinal tract.
When transmission occurs through a vector, which is a nonhuman carrier such as
an animal or insect, it is known as vector-borne transmission. Common vectors
include bats, fleas, lice, mosquitoes, raccoons, rats, skunks, squirrels, and ticks.
During vector-borne transmission, the infectious agent may be transported
mechanically without multiplication or change, or the infectious agent may
develop biologically before passage to a susceptible host. Diseases transmitted
through vectors prove challenging in communicable disease control, because
individuals who become infected typically have no direct personal contact with
other infected persons. Rather, isolated cases occur within areas inhabited by the
vector. Nevertheless, human history has been significantly affected by vectorborne diseases. Mosquito borne malaria and snail-borne schistosomiasis cause
major human suffering to hundreds of millions of people in tropitropical settings
every year. The fact that most of these diseases are endemic to certain areas
suggests the need for tight controls for prevention and intervention.
Control strategies directed toward vector-borne diseases typically involve, in
addition to community education, complex environmental measures to hinder the
vector from reaching the host .
These strategies may include
• Reducing the population of insect vectors (eg, by spraying insecticides to kill
• Treating the natural habitat of the vector to reduce the population density
• Reducing the population of other animal hosts that harbor the vector, as when rats
are exterminated to reduce the risk of plague
• Erecting barriers between the susceptible human and the vector, such as use of
mosquito nets or screened windows to control malaria or protective clothing and
sprays against tick-borne diseases
• Educating the public about preventive and protective measures, including actions
to take when attacked by the vector to prevent disease from developing
Airborne Transmission
Airborne transmission occurs through droplet nuclei—the small residues that result
from evaporation of fluid from droplets emitted by an infected host. They may also
be created purposely by atomizing devices or accidentally in microbiology
laboratories. Because of their small size and weight, they can remain suspended in
the air for long periods before they are inhaled into the respiratory system of a
Airborne transmission can also occur in dust. Small particles of dust from soil
containing fungus spores may cling to clothing, bedding, or floors. Alternatively,
the spores may become separated from dry soil by the wind and then be inhaled by
the host
Chain of causation in infectious disease
Epidemiologist used Chain of causation to explain the conditions developed and
offer effective prevention and protection.
The chain consist of, reservoir, portal of exist, mode of transmission, agent, portal
of entry, and the host
First link : The chain begins by (reservoir) where causal agent can live and
multiply) for example in plague, the reservoir is may be other human, rats, and few
other animals. In Malaria, the reservoirs for the parasitic agent are the infected
Second link: Portal of exist: from the reservoir, the bites of an Anopheles
mosquito provide a portal of exist for the parasite, which spend part of its life cycle
in the mosquito body
Third link: Mode of transmission: The method of transmission is the means by
which the agent goes from the source to the host. For example (The mosquitoes are
the mode of transmission)
There are four major methods of transmission:
Contact transmission: the agent is spread
 Direct contact transmission takes place when organisms are transmitted
directly from the source to the susceptible host without involving an
intermediate object; this is also referred to as person-to-person transmission.
An example is the transmission of hepatitis A virus from one individual to
another by hand contact.
 Indirect transmission occurs when the organisms are transmitted from a
source, either animate or inanimate, to a host by means of an inanimate
object. An example is transmission of Pseudomonas organisms from one
individual to another by means of a shaving brush.
1. Common-vehicle transmission refers to agents transmitted by a common
inanimate vehicle, with multiple cases resulting from such exposure.
Vector borne transmission, in which arthropods are the vectors. Vector
transmission may be external or internal. External, or mechanical,
transmission occurs when organisms are carried mechanically on the
vector, this category includes diseases in which food or water as well as
drugs and parenteral fluids are the vehicles of infection. Examples include
 Food-borne salmonellosis,
 Waterborne shigellosis, and bacteremia resulting from use of intravenous
fluids contaminated with a gram-negative organism.
 The third method of transmission, airborne transmission, refers to infection
spread by droplet nuclei or dust. To be truly airborne, the particles should
travel more than 3 feet through the air from the source to the host. Droplet
nuclei are the residue from the evaporation of fluid from droplets, are light
enough to be transmitted more than 3 feet from the source, and may remain
airborne for prolonged periods. Tuberculosis is primarily an airborne
disease; the source may be a coughing patient who creates aerosols of
droplet nuclei that contain tubercle bacilli. Infectious agents may be
contained in dust particles, which may become re-suspended and transmitted
to hosts. An example occurred in an outbreak of salmonellosis in a newborn
nursery in which Salmonella-contaminated dust in a vacuum cleaner bag
was re-suspended when the equipment was used repeatedly, resulting in
infections among the newborns. An example of a disease that may be spread
by droplets is measles.
An infectious agent may be transmitted by more than one route.
For example, Salmonella may be transmitted by a common vehicle (food) or by
contact spread (human carrier). Francisella tularensis may be transmitted by any
of the four routes
Mode Of Transmission
(direct ontact, airborne or
droplet, blood, sexual
Diphtheria, Gonorrhea
H. influenzae b
Cholera, E. coli.
Q fever
Meningococcal disease
Pertussis, Syphilis
Group A & B streptococcus
Head lice
Typhoid fever
Chickenpox, Cold viruses
Ebola haemorrhagic fever
Hepatitis B and C
Herpes, Influenza
Measles, Mumps, Rubella
Hepatitis A
pulmonary syndrome
Yellow fever
Valley fever
Fourth link: Agent The next link in chain is the agent itself, in Malaria; the agent
is the protozoa that multiply in mosquito
Fifth link: Then the portal of entry, the bite by mosquito provides the portal of
entry into the human host. The organism may enter the host through the skin,
mucous membranes, lungs, gastrointestinal tract, or genitourinary tract, and it may
enter fetuses through the placenta
Sixth link: Host: The last link in the chain
Development of disease in a host is influenced by host defense mechanisms in
addition to other factors as sex, age…etc.
Environment have a profound influence at any point along the chain for example
Temperature can assist or inhibit multiplication of organisms at their reservoir; air
velocity can assist the airborne movement of droplet nuclei; low humidity can
damage mucous membranes; and ultraviolet radiation can kill the microorganisms.
In any investigation of disease, it is important to evaluate the effect of
environmental factors. At times, environmental control measures are instituted
more on emotional grounds than on the basis of epidemiologic fact. It should be
apparent that the occurrence of disease results from the interaction of many factors
Application of chain of causation using in infectious disease to illustrate to
explain spread of Malaria
Chain link
Infected human with malaria is
the reservoir for parasitic agent
other animals as monkey
Portal of exist
infected human
of Vector born /Mosquito
Protozoa multiply in mesquite
Portal of entry
uninfected human
Human become infected with
Malaria breed in hot , high
humidity environment
Prevention of infectious diseases
Primary prevention
In the context of communicable disease control, two approaches are useful in
achieving primary prevention:
1. Education using mass media and targeting health messages to aggregates ;
Education Health education in primary prevention is directed both at helping atrisk individuals understand their risk status and at promoting behaviors that
decrease exposure or susceptibility.
Use of Mass Media for Health Education
Use the media as a primary change agent; community education programs can
successfully increase knowledge about communicable diseases and preventive
Targeting Meaningful Health Messages to Aggregates
To effectively deliver a communicable disease prevention message, the message
must reach the target (at-risk) population.
This requires correct identification of the characteristics of the target audience, in
terms of educational level, salience of the issue, involvement of the target audience
with the issue, and access of the target audience to the media channels used.
2. Immunization
Control of acute communicable diseases through immunization has been a
common practice since the 19th century in the United States. Immunization is the
process of introducing some form of disease-causing organism into a person’s
system to cause the development of antibodies that will resist that disease
Vaccine-Preventable Diseases
Immunity may be either passive or active.
Passive immunity is short-term resistance to a specific disease- causing organism;
it may be acquired naturally (as with newborns through maternal antibody transfer)
or artificially through inoculation with a vaccine that gives temporary resistance.
Such immunizations must be repeated periodically to sustain immunity levels. An
example is the influenza vaccination.
Active immunity is long-term (sometimes lifelong) resistance to a specific
disease-causing organism; it also can be acquired naturally or artificially.
Naturally acquired active immunity occurs when a person contracts a disease
and develops long-lasting antibodies that provide immunity against future
Artificially acquired active immunity occurs through inoculation with a vaccine,
such as the diphtheria, pertussis, tetanus vaccination series given to children.
A vaccine is a preparation made from killed, living attenuated or living fully
virulent organisms that is administered to produce or artificially increase immunity
to a particular disease.
Examples of "live" (example attenuated) vaccines include:
Viral: measles vaccine, mumps vaccine, rubella vaccine, chicken pox
vaccine, oral polio vaccine (Sabin), yellow fever vaccine,[2] and nasal-spray
flu vaccine (including the seasonal flu nasal spray and the 2009 H1N1 flu
nasal spray). Rabies vaccines are now available in two different attenuated
forms, one for use in humans, and one for animal usage.
Bacterial: BCG vaccine,[2] typhoid vaccine[3]
Herd immunity is central to understanding immunization as a means of protecting
community health. It is the immunity level present in a particular population of
people (Chin, 1999).
If there are few immune persons within a community, there is low herd immunity
and the spread of disease is more likely. Vaccination of more individuals in the
community, so that a high proportion have acquired resistance to the infectious
agent, contributes to high herd immunity. High herd immunity reduces the
probability that the few unimmunized persons will come in contact with one
another, making spread of the disease less likely. Outbreaks may occur if the
immunization rate falls to less than 85% (Scutchfield & Keck, 2001) or if
unimmunized susceptible persons are grouped together rather than dispersed
throughout the immunized community. An example of lack of herd immunity is
presented in The Global Community
Barriers to Immunization Coverage
Improving immunization coverage requires examination of reasons that children
are not immunized. Many barriers exist.
They include religious, financial, social, and cultural factors; philosophical
objections; and provider limitations that form barriers to adequate immunization.
Religious Barriers The right to religious freedom gives some groups of
individuals in the United States the constitutional right to exemption from
immunization if they object to vaccination on religious grounds. Children from
these families are identified at school entry. Such exemptions must be specifically
enacted by law, and, although it is not necessary to belong to a specific
denomination, courts have required those seeking exemption to demonstrate that
such belief against immunization is sincere and that no clear danger exists from the
particular disease. Problems arise when members of exempted groups are found
together in school or community settings, raising the risk of disease spread because
of a lower herd immunity.
Financial Barriers Until recently, finances may have been significant in
accounting for immunization delays in families with limited incomes. Such
families may have had more immediate priorities than vaccinations for an
otherwise well child. In the late 1990s, two major initiatives significantly improved
the financing of childhood immunizations.
Social Barriers: Educational levels, transportation problems, and access to and
overcrowding of facilities pose further barriers to adequate immunization
Cultural Barriers: Meeting the immunization needs of minority groups may
involve cultural barriers related to differing concepts of health care and preventive
measures between cultures. Language barriers may intervene to make parents feel
confused, overwhelmed, and unable to access services.
Philosophical Objections: Many affluent, well-educated, caring parents have
philosophical objections to immunization.
They fear harm to their children, as has periodically been reported in the media.
Parents may object to one or more of the vaccines or prefer to delay or separate the
vaccines; this puts the child “behind” in immunizations, according to the AAP
schedule. Community health nurses should be aware that caring parents are talking
about these issues, reading about them, and trying to make informed decisions
about them.
Provider Limitations : Another barrier to immunization coverage is provider
limitations. Health care providers may have contact with an eligible child, yet fail
to offer vaccination. This occurs when providers see children for different reasons
and do not review their immunization records, missing the opportunity to provide
vaccination services at what may be a very convenient time for parents.
Secondary Prevention
There are two approaches to secondary prevention of communicable disease: (1)
screening and (2) contact investigation, partner notification, and case-finding
The term screening is used in community health and disease prevention to
describe programs that deliver a testing mechanism to detect disease in groups of
asymptomatic, apparently healthy individuals. Familiar examples include (1) or
Venereal Disease Research Laboratory (VDRL) test. The tine and Mantoux
tuberculin tests for TB are common screening measures. For HIV, the HIV-1/HIV2 antibody tests or a sensitive screening test such as the enzyme immunoassay
(EIA), confirmed by a supplemental test such as the Western blot or an
immunofluorescence assay (IFA) are used (CDC, 2002c).
Screening is a
secondary prevention method because it discovers those who may have
already become infected in order to initiate prompt early treatment.
Tertiary Prevention
The approaches to tertiary prevention of communicable disease include isolation
and quarantine of the infected person and safe handling and control of
infectious wastes.
Isolation and Quarantine
Communicable disease control includes two methods for keeping infected persons
and non infected persons apart to prevent the spread of a disease.
Isolation refers to separation of the infected persons (or animals) from others for
the period of communicability to limit the transmission of the infectious agent to
susceptible persons.
Quarantine refers to restrictions placed on healthy contacts of an infectious case
for the duration of the incubation period to prevent disease transmission if
infection should develop
Safe Handling and Control of Infectious Wastes
Also important to the control of infection in community health is the proper
disposition of contaminated wastes. The CDC has developed universal precautions,
which encourage health care workers to think of all blood and body fluids, and
materials that have come in contact with them, as potentially infectious
(Chin, 1999). The universal precautions include the following:
• Basic hand-washing after contact with the client or with potentially contaminated
articles and before care of other clients
• Appropriate discarding or bagging and labeling of articles contaminated with
infectious material before it is sent for decontamination and reprocessing
• Appropriate isolation based on the mode of transmission of the specific disease,
which may include strict isolation, contact isolation, respiratory isolation, TB
isolation (AFB isolation), enteric precautions, or drainage/secretion precautions
The Environmental Protection Agency (EPA) defines infectious waste as “waste
capable of producing an infectious disease.” The agency notes that for waste to be
infectious, it must contain pathogens with sufficient virulence and quantity so that
exposure to the waste by a susceptible host could result in an infectious disease.
EPA requirements for medical waste disposal are for waste to be segregated into
categories of (1) sharps; (2) toxic, hazardous, regulated, or infectious fluids of
greater than 20 mL; and (3) other materials.
Although incineration has long been recognized as an efficient method for
disposing safely of sharps and other contaminated medical waste, fewer
incinerators are available now, with increasing regulation of emissions, particularly
regulations related to the burning chemical wastes.
Four key elements of an infectious waste management program are applicable to
community practice:
Health professionals must be able to correctly distinguish waste that poses a
significant infection hazard from other biomedical waste that poses no greater
risk than general municipal waste, and such infectious waste must be clearly
The waste management program must have administrative support and
authority to institute practice guidelines and provide the containers and other
resources needed for safe disposal of infectious wastes.
Handling of the infectious wastes must be minimized. Containers should be
rigid, leak resistant, and impervious to moisture; they should have sufficient
strength to prevent rupture or tearing under normal conditions; and they should
be sealed to prevent leakage. Containers for sharps must also be puncture
There must be an enforcement or evaluation mechanism in place to ensure
that the goal of reducing the potential for exposure to infectious waste in the
community is met.
Six Components of the Chain of Disease and Strategies for Breaking the
1. Causative Agent
Definition :
Biological, physical, or chemical agent capable of causing disease.
Strategies for breaking this link.
 Remove or reduce the number of microbes through hand washing.
 Eliminate and destroy microbes using sterilization techniques.
 Use antibiotics and antimicrobials prudently.
 Conduct surveillance for infectious pathogens at all levels.
2. Reservoir
Definition —
Location where an infectious agent may survive, but may or may not multiply.
Microbes causing nosocomial infections may be found in patients, healthcare
workers, equipment, or healthcare facilities.
Strategies for breaking this link:
 Eliminate contaminated equipment through thorough sterilization or the use
of disposable supplies.
 Isolate infectious patients when appropriate.
 Relieve infected healthcare workers from duty until non contagious.
3. Portal of Exit
Pathway by which an infectious agent exits or leaves the reservoir, such as via the
respiratory or gastrointestinal tract or the blood.
Strategies for breaking this link —
 Contain infectious microbes, for example, cover the mouth and nose when
coughing or sneezing.
 Use gloves when in contact with any body fluids.
4. Mode of Transmission
Definition —
The medium or mechanism through which an infectious agent moves from a
reservoir to a susceptible host. Transmission of a disease may be through contact
(direct, such as person-to-person, or indirect through contaminated instruments,
linens, or dressings), common vehicle (eg., contaminated food), airborne (eg., TB),
or vector-borne (eg., malaria).
Strategies for breaking this link —
 Disrupt direct contact transmission by washing hands after patient contact.
 Interrupt indirect contact by using bags/covered containers for isolating
contaminated material.
 Prevent contamination of common vehicles, such as adequately refrigerating
food in hospitals.
 Eliminate vectors through public health measures, such as water drainage in
mosquito-ridden areas to prevent malaria and West Nile Fever where
outbreaks have occurred.
5. Portal of Entry:
Definition —
Pathway by which the infectious agent enters the susceptible host; examples
include the respiratory and genitourinary tracts, broken skin, or placenta.
Strategies for breaking this link —
 Keep the door closed in respiratory-isolation patient rooms.
 Use masks when caring for patients with -TB.
6. Susceptible Host:
Definition —
Person (or animal) who lacks sufficient resistance to a specific pathogenic
organism. Factors influencing susceptibility include age, gender, ethnicity,
occupation, nutritional status, current medications, concomitant disease, genetics,
socioeconomic status, and lifestyle.
Strategies for breaking this link —
 Use vaccines, such as the hepatitis B vaccine, for healthcare workers.
 Employ vaccines for high-risk population, such as influenza inoculation for
the elderly and those with respiratory conditions.
 Screen healthcare workers
 Support public health interventions that address such areas as nutrition,
potable water, and vector control.
Natural history of a disease or health condition
Natural history; events that occur before its development, during its course and
during its conclusion and this involve interaction among susceptible host, causative
agent and environment
Natural history of disease occurs in 2 phases
Phase one
“Pre-pathogenesis” : before the deductibility of disease or
condition and this stage composed of 2 stages
 Susceptibility during this stage disease is not present and individual
have not been exposed
 Adaptation
Pathogenesis : while disease or condition is present
 Onset and early clinical stage
 Culmination and late stage
Stage 1
Stage 2
Stage 3
Stage 4
Early clinical stage Late clinical stage
Early pathogenesis
Primary prevention
Secondary prevention
Public Health Measures to Prevent Infectious Diseases
 Safe water
 Sewage treatment and disposal
 Food safety programs
 Animal control programs
 Vaccination programs
 Public health organizations
Role of the community health nurse
 Information gathering
Tertiary prevention
Assessment includes full family history, recurrent pattern of disease , presence of
risk factors in individual's environment is essential part of counseling .
 Record keeping and notification
 Accurate recording.
 Policy maker
 Ethical policy decision regarding services
 Maintain detailed specialist knowledge and keeping in research.
 Recognizing disease patterns within the family and community illustrating a
particular mode of transmission.
 Calculating risks of spreading and transmission and outbreak
 Allocating sufficient time to consider all implications of a disease
 Storing and analyzing all information , allows all individuals on a register
to be contacted if new tests or treatment become available
 Care provider
Nurses are among the many care providers who make up the
interdisciplinary team .
The nursing profession sets the standard for providing care in the community .
 Counseling
 Educator
Community health nurse educate client , other nurses and the public
about the health related problems they discover and the roles of the nurses who
work to resolve these problems , therapy improving health .
 Teaching about nature of the disease.
 Mechanics of transmission .
The nurse provide information and giving reassurance and clarify issues that
troubling the patient .
 Help the patient in design making .
 Advocator
The role of advocate is filled when a person acts foe another person in a
way that is reasonable and prudent . Acting for another is necessary when the
person can not get his or her own health care needs met independently .
 Planner
Community health nurse are involved in health planning in an effort to
meet the needs of community .Health planning should include the client
whenever possible so that health care services are relevant or client needs .
 Coordinator of care
Community health nurses coordinate the care of clients to resources as
well as to provide appropriate services . Care must be coordinate to avoid the
duplication of services .
Emerging and Re-emerging Infectious Diseases
Fifty years ago many people believed the age-old battle of humans against infectious disease was
virtually over, with humankind the winners. The events of the past two decades have shown the
foolhardiness/ stupidity of that position. At least a dozen "new" diseases have been identified
(such as AIDS, Legionnaire disease, and hantavirus pulmonary syndrome), and traditional
diseases that appeared to be "on their way out" (such as malaria and tuberculosis) are resurging.
Globally, infectious diseases remain the leading cause of death, and they are the third leading
cause of death in the United States. Clearly, the battle has not been won.
Emerging infectious diseases are diseases that (1) have not occurred in humans before (this type
of emergence is difficult to establish and is probably rare); (2) have occurred previously but
affected only small numbers of people in isolated places (AIDS and Ebola hemorrhagic fever are
examples); or (3) have occurred throughout human history but have only recently been
recognized as distinct diseases due to an infectious agent (Lyme disease and gastric ulcers are
Re-emerging infectious diseases are diseases that once were major health
problems globally or in a particular country, and then declined dramatically, but
are again becoming health problems for a significant proportion of the population
(malaria and tuberculosis are examples). Many specialists in infectious diseases
include re-emerging diseases as a subcategory of emerging diseases.
A review of Figure 8 reveals some explanations for the re-emergence of infectious diseases.
Tuberculosis has re-emerged due to evolution of the causative bacteria. The pathogen has
acquired resistance to the antibiotics used to treat tuberculosis (either through mutation or
genetic exchange) and the long-term use of antibiotics (both within one individual and across the
population) has selected for the pathogen's proliferation. Malaria has also become drug resistant,
and the vector mosquito has acquired resistance to pesticides as well. The re-emergence of
diseases such as diphtheria and whooping cough (pertussis) is related to inadequate vaccination
of the population. When the proportion of immune individuals in a population drops below a
particular threshold, introduction of the pathogen into the population leads to an outbreak of the
Modern Threat: Emerging & Re-Emerging Infectious Diseases
The success of antibiotics after World War II led to the impression that bacterial
infections could be easily cured. "Infectious Diseases are more easily prevented
and more easily cured than any other major group of disorders..." stated Harrison's
Principles of Internal Medicine 10th ed., 1983. Although many viral diseases
remained unconquered, effective vaccines prevented some of the most frightening
ones. Much of the industrialized world basked in a feeling of invulnerability,
assuming that heart disease and cancer were the major health problems left to
Global microbial threats in the 1990s
Today we view infectious disease with greater respect. The victories
of the past are seen in perspective with the emergence of HIV/AIDS and at least 30
other new infections. Old foes such as tuberculosis, rabies, malaria, and pneumonia
are evading traditional therapies and are now on the comeback. Infectious diseases
are the leading cause of death in the world and the third leading cause of death in
the United States. What is happening to make it easier for these deadly microbes to
infect us?
Changes in Land Use
• Dams to store water for irrigation and electric power introduce water
born disease
The risk of many infectious diseases is influenced by human alteration of
local, regional or global ecosystems. In the tropics and subtropics, dams created to
store water for irrigation and hydroelectric power have introduced water-borne
diseases, such as schistosomiasis, to communities where they previously did not
Human activities, such as deforestation, irrigation, extensive
agriculture or building settlements, affect the ecological conditions in which
disease-causing microbes thrive.
Urbanization - Megacities
Population density is increasing in countries that are not able to provide adequate
sewage systems, safe drinking water, housing and medical facilities. People are
living in overcrowded "megacities" often million or more, many of which are in
tropical or subtropical regions where infectious diseases thrive. Today there are
over 24 megacities, mostly in developing countries. It is estimated that by 2010,
50% of the world's population will be living in urban areas.
Economic conditions encourage the mass movement of workers from rural
areas to cities. Rural urbanization allows infections that may once have remained
obscure and localized in isolated rural areas to reach larger populations. Urban
slums are breeding-grounds for physical disease and social ills, ranging from
tuberculosis to drug abuse.
Globalization of World Commerce
We eat out from the world's gardens, but not all are well-kept. Raspberries from Guatemala made
thousands of Americans ill from a parasite called cyclospora, which was in the water used to
spray and irrigate the raspberries. Potential disease-carrying insects and contaminated foods,
plants, and other products cross U.S. borders every day. Since the 1980's, food imports to the
U.S. have doubled. Increases in food imports strain the nation's food safety system. While we
rely on the FDA, USDA and other government agencies to protect our food supply, inspections
have dropped to half of what they were five years ago. As the world's nations become more
intertwined, interdependent and intensely competitive, will the rest of the world's standards
become more like those of the U.S. or will the U.S., despite high standards, become more
vulnerable to the rest of the world's microbes?
Population Movement
In 1990 it was estimated that there were 20 million refugees and 30 million displaced persons
worldwide. Human population movements due to political, economic or climatic events such as
flooding, earthquakes and drought, are important factors in disease emergence. Such crises lead
to interim living arrangements, such as refugee camps and temporary shelters, that provide ideal
conditions for the spread of infections. Temporary living quarters often share similarities with
urban slums - crowding, inadequate sanitation, limited access to medical care, lack of clean
water and food, dislocation, and inadequate barriers for disease-carrying agents.
An example is the movement of 500,000 - 800,000 Rwandan refugees into Zaire in 1994.
Almost 50,000 refugees died during the first month from cholera and Shigella dysenteriae type 1
that swept through the refugee camps.
Increased Air Travel
Modern air travel makes it possible to spread infectious diseases to different parts of the world.
People are traveling to areas where they can get infected and bring new diseases home with
them. How many more victims could a lethal strain of influenza, similar to the 1918 epidemic,
claim today with half a billion passengers traveling via jet planes? The speed of travel enables a
person carrying a disease such as Ebola to travel 12,000 miles, pass unnoticed through customs
and immigration before developing symptoms several days later, thus infecting many other
people before getting ill.
Microbial Adaptation: Tuberculosis
Tuberculosis is an acute or chronic infection caused by Mycobacterium tuberculosis, which
usually involves the lungs but may involve any organ or tissue of the body. A worldwide health
problem that reached a peak in the l9th century, it was thought to have been brought under
control by the l960s due to active public health measures and the use of modern drug therapies.
However, this complacency led to reduced funding for the diagnosis and treatment of TB at the
same time that the bacterium was developing resistance to the drugs used to treat it. The problem
has been compounded since the 1980s by the emergence of a new population of vulnerable
individuals - those infected with HIV.
Living In A World With HIV/Aids
Sharing needles for drug injection is a well-known route of HIV transmission as well as many
blood-borne infections. Injection drug use contributes to the spread of infectious diseases far
beyond the circle of those who inject. People who have sex with an injection drug user (IDU) are
also at risk for infection through sexual HIV transmission.
Antibiotic Abuse
Just as any organism adapts to changes in its environment, so the use of antibiotics has become a
feature of the environment in which bacteria breed. Because bacteria multiply rapidly, there are
many opportunities for mutations to occur under the selective pressure of antibiotics. As such,
many strains of bacteria have now developed resistance to many common antibiotics. The
routine use of antibiotics in breeding cattle, for example, is one probable source of resistant
Many infectious diseases, once curable by antibiotics, are reappearing in forms that are difficult
and sometimes impossible to treat with conventional drugs. Scientists warn that measures are not
taken now to slow their spread, the day of untreatable common infections may return.
New antibiotics are constantly being developed to combat the problem of antibiotic resistance.
Research on the genetics of bacteria using advanced molecular genetic technologies may provide
new opportunities to develop specific antibiotics for certain bacteria
Global successes and failures to control communicable diseases are affected by a
bevy of factors.
First, the geopolitical nature of an area influences who can respond when a
communicable disease occurs in a country.
Second, the natural and manmade resources of an area influence the health status
of the population before a disease strikes, contributing to both disease resistance
and the ability to survive once a communicable disease is contracted. This is one
reason that poorer nations have higher incidences and greater numbers of deaths
from communicable diseases.
Finally, weather and climatic factors can influence health and illness. For
example, both droughts and floods can lead to crop failure and subsequent famine.
Other such factors include hurricanes, monsoons, earthquakes, tornadoes, floods,
and fire.