Transcript classifying diseases

CLASSIFYING DISEASES

Acute Diseases
• Acute diseases are those conditions in which the peak
severity of symptoms occurs within three months
(usually sooner), and recovery in those who survive is
usually complete

Chronic Diseases
• Chronic diseases or conditions are those in which
symptoms continue longer than three months and in
some cases for the remainder of the person’s life.
Recovery is slow and sometimes incomplete.
CLASSIFYING DISEASES (cont’d.)

Communicable (Infectious) Diseases
• Diseases for which biological agents or their products are the cause
and which are transmissible from one individual to another
• The disease process begins when the causative agent is able to
lodge and grow or reproduce within the body
• The process of lodgment and growth of a microorganism or virus
in the host is termed infection

Non-communicable (Noninfectious) Diseases/Illnessses
• Those diseases or illnesses that cannot be transmitted from an
infected person to a susceptible, healthy one
• Several, or even many, factors may contribute to the development
of a given non-communicable health condition
• The contributing factors may be genetic, environmental, or
behavioral in nature
Classification of Diseases
Types of Diseases_____Examples______________

Acute Diseases
• Communicable
• Non-communicable
(incl. trauma)

Common cold, pneumonia, mumps,
measles, pertussis, typhoid fever, flu
Appendicitis, poisoning, trauma (e.g.,
due to automobile accidence, fires,
etc.)
Chronic Diseases
• Communicable
• Non-communicable
Lyme disease, tuberculosis, AIDS,
syphilis, rheumatic fever following
streptococcal infections, herpes
Diabetes, coronary heart disease,
osteoarthritis, cirrhosis of the liver dur
to alcoholism, hyptertension
DEATH RATES PER 100,000 POPULATION
1900 - 1989
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LEADING UNDERLYING MORTALITY CAUSED
BY INFECTIOUS DISEASES IN THE UNITED
STATES, 1980 AND 1992
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Host
Agent
Environment
COURSE OF INFECTIOUS DISEASE




Exposure/Invasion of Host
Incubation -- period of time between exposure and onset of
symptoms -- e.g., interval between HIV infection and
development of AIDS can be as long as 10-15 years
Host reaction
Disease runs course -- treatment, recovery/death (most
people don’t die from infectious diseases)
INCUBATION PERIOD

Varies by disease
 Salmonella -- 12-72 hours after infection; symptoms
usually resolve in 5-7 days, unless infected person is in a
very weakened health status
 Measles (rubeola) -- approx. 10-12 days (prodomal -- i.e.,
interval between the earliest symptoms and the appearance
of the rash or fever -- rash onset, on average, 14 days
 HIV -- 6 weeks upward to months; interval between HIV
infection and development of AIDS can be as long as 1015 years
 2-6 weeks after infection in many, but not all, diseases,
most people develop antibodies against reinfection
CHAIN OF INFECTION ILLUSTRATION
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HOST, ENVIRONMENT, VECTOR AND
AGENT RELATIONSHIPS
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MODES OF COMMUNICABLE DISEASE
TRANSMISSION

Direct Transmission

Indirect Transmission
DIRECT TRANSMISSION

Immediate transfer of the disease agent by direct contact
between the infected and the susceptible individuals

Occurs through such acts as touching, biting, kissing,
sexual intercourse, or by direct projection (droplet spread)
by coughing or sneezing within a distance of one meter

Examples of diseases for which transmission is usually
direct are AIDS, syphilis, gonorrhea, and the common cold
INDIRECT TRANSMISSION

May be one of three types: air-borne, vehicle-borne, or
vector-borne

Air-borne transmission -- transmission of microbial
aerosols to a suitable port of entry, usually the respiratory
tract
• Microbial aerosols are suspensions of dust or droplet
nuclei made up wholly or in part by microorganisms -may be suspended and infective for long periods of
time
• Examples of air-borne diseases include tuberculosis,
influenza, histoplasmosis, and legionellosis
INDIRECT TRANSMISSION (cont’d.)

Vehicle-borne transmission -- contaminated materials or
objects (fomites) serve as vehicles, nonliving objects by
which communicable agents are transferred to a
susceptible host
• The agent may or may not have multiplied or developed
on the vehicle
• Examples of vehicles include toys, handkerchiefs,
soiled clothes, bedding, food service utensils, and
surgical instruments
• Also considered vehicles are water, milk, food (e.g.,
common vehicles), or biological products such as blood,
serum, plasma, organs and tissues
• Almost any disease can be transmitted by vehicles,
including those for which the primary mode of
transmission is direct, such as dysentery and hepatitis
INDIRECT TRANSMISSION (cont’d.)

Vector-borne transmission -- disease transfer by a living
organism, such as a mosquito, fly, or tick
• Transmission may be mechanical, via the contaminated
mouth parts or feet of the vector, or biological,
involving multiplication or developmental changes of
the agent in the vector before transmission occurs
• In mechanical transmission, multiplication and
development of the disease do not usually occur -- e.g.,
organisms that cause dysentery, polio, cholera, and
typhoid fever have been isolated from such insects as
cockroaches and house flies and could presumably be
deposited on food prepared for human consumption
INDIRECT TRANSMISSION (cont’d.)
• In biological transmission , multiplication and/or
developmental changes of the disease agent occur in the
vector before transmission occurs
• Biological transmission is much more important than
mechanical transmission in terms of its impact on
public/community health
• Examples of biological vectors include mosquitoes,
fleas, ticks, lice, flies and other insects
INDIRECT TRANSMISSION (cont’d.)
• Mosquitoes are extremely important vectors of human
diseases -- e.g., they transmit the viruses that cause
yellow fever and dengué fever as well as 200 other
viruses -- they also transmit malaria, which infects 100
million people in the world each year (most in tropical
areas), killing at least 1 million of them each year
• Ticks are another important biological vector,
transmitting Rocky Mountain spotted fever, relapsing
fever, and Lyme disease
FOOD-BORNE DISEASES IN THE U.S.
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CHAIN OF INFECTION MODEL SHOWING
DISEASE PREVENTION AND CONTROL
STRATEGIES
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DISEASE AND INJURY PREVENTION
AND CONTROL

Prevention
• Includes individual, clinical, or personal health services
such as immunizations, screening for high blood
pressure and follow-up services, or the use of Pap
smears to detect the precursors to cancer of the cervix

Protection
• Includes the activities of organizations, both public and
private, to reduce exposure to hazards such as polluted
water, contaminated food, traffic accidents, mosquitoes,
or use of electric saws without safety devices
TABLE: Comparison of Maximum and Current
Morbdity due to Vaccine-Preventable
Diseases
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PREVENTION OF COMMUNICABLE
DISEASES

Primary Prevention
• In the chain of infection model, primary prevention
strategies are evident at each link of the chain
• Successful application of each strategy can be seen as
weakening the link -- with the ultimate goal of
interrupting the disease transmission cycle
• Community measures -- e.g., chlorination of the water
supply, inspection of restaurants, immunization
programs that reach all citizens, maintenance of a wellfunctioning sewer system, proper disposal of solid
waste, and control of vectors and rodents
PREVENTION OF COMMUNICABLE
DISEASES (cont’d.)
• Personal/Individual actions -- hand washing, proper
cooking of foods, adequate clothing and housing, use of
condoms, obtaining all of the available immunizations
against specific diseases
PREVENTION OF COMMUNICABLE
DISEASES (cont’d.)

Secondary Prevention
• Community effort includes measures taken to control
or limit the extend of a disease outbreak/epidemic -e.g., maintaining records of cases and compliance with
regulations requiring the reporting of notifiable
diseases, investigating cases and contacts, those who
may have become infected through contact with cases
• Individual effort includes either (1) self-diagnosis and
self-treatment with nonprescription medications or
home remedies, or (2) diagnosis and treatment with an
antibiotic or other physician-prescribed medicine
PREVENTION OF COMMUNICABLE
DISEASES (cont’d.)
• Occasionally, secondary disease control measures may
include isolation or quarantime
• Isolation = separation, for the period of
communicability, of infected persons or animals from
others so as to prevent the direct or indirect
transmission of the communicable agent to a
susceptible person/host
• Quarantine = limitation of the freedom of movement of
well persons or animals that have been exposed to a
communicable disease until the incubation period has
passed
PREVENTION OF COMMUNICABLE
DISEASES (cont’d.)
• Further measures may include disinfection -- the killing
of communicable agents outside the the host, and mass
treatment with antibiotics
• Public health education and health promotion should
also be used as both primary and secondary preventive
measures
PREVENTION OF COMMUNICABLE
DISEASES (cont’d.)

Tertiary Prevention
• Convalescence from infection, recovery to full or
partial health, and return to normal activity
• In some cases, such as paralytic polio, return to normal
activity may not be possible, even with extensive
physical therapy
• At the community level, proper removal of infected
items such as clothing, disinfection, and burial of the
dead, for example
• Tertiary prevention may also involve the reapplication
of primary and secondary measures to prevent further
cases -- e.g., in Japan and South Korea, people with
colds or flu wear gauze masks in public to reduce the
spread of the disease
TOOLS AVAILABLE TO THE “STATE”
FOR THE CONTROL OF
COMMUNICABLE DISEASE




REPORTING -- Physicians and other health professionals
must report specified diseases to a designated authority,
usually to local or state health authority
LABORATORY REPORTING -- In many states,
licensed laboratories must report positive results for certain
diseases to the health department, even though a diagnosis
may not have been established
SURVEILLANCE -- The systematic measurement of
health status and risk factors
MONITORING -- Involves the ongoing assessment of a
condition after intervention has been initiated
TOOLS AVAILABLE TO THE “STATE”
FOR THE CONTROL OF
COMMUNICABLE DISEASE


LABORATORY ANALYSIS -- Involves public health
laboratories with authority for the study and detection of
infectious diseases
CONTACT INVESTIGATION -- Once a case of a
particular disease has been diagnosed, personnel from the
health department are authorized to interview the victim to
establish a list of possible contact. (A practice of
considerable debate recently because of AIDS.)
TOOLS AVAILABLE TO THE “STATE”
FOR THE CONTROL OF
COMMUNICABLE DISEASE

TREATMENT -- Public health agencies are required to
provide treatment services for specified infectious diseases.
(In many cities, special hospitals were built for this
purpose.) Local health departments are also required to
provide services for people infected with sexually
transmitted diseases or tuberculosis. These services are not
regarded as welfare services but rather as tools to prevent
the spread of dangerous communicable diseases. It is
important to note, however, that the state cannot require
treatment. The state can only force treatment if it can
prove that the victim is (1) gravely disabled, and (2) a
danger to self or others because of the disability
TOOLS AVAILABLE TO THE “STATE”
FOR THE CONTROL OF
COMMUNICABLE DISEASE


ISOLATION -- Means separation of infected people from
non-infected people during the period of communicability.
Follows the “least restrictive” principle
IMMUNIZATION -- All states have requirements for the
immunization of children against certain infectious
diseases -- most common are diphtheria, pertussis
(whooping cough), tetanus, rubella (German measles), and
polio. The controlling agency is usually the school system,
which is required to prevent entry of any child who has not
been properly immunized
TOOLS AVAILABLE TO THE “STATE”
FOR THE CONTROL OF
COMMUNICABLE DISEASE

INVESTIGATION -- In addition to the specific
authorities noted above, most health departments are
required to investigate unusual occurrences of disease or
injury. This includes the authority to review medical
records, to perform laboratory investigations, to examine
patients, and to interview both patients and others who
may have been exposed to the disease or injury. (The
public health authorities may require court authorization to
undertake these investigations.)