CLASSIFYING DISEASES w Acute Diseases Acute diseases are those conditions in which the peak severity of symptoms occurs within three months (usually sooner),

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 DiseasesTypes of Diseases_____Examples______________

Acute Diseases• Communicable Common cold, pneumonia, mumps,

measles, pertussis, typhoid fever, flu

• Non-communicable Appendicitis, poisoning, trauma (e.g., (incl. trauma) due to automobile accidence, fires,

etc.)

Chronic Diseases• Communicable Lyme disease, tuberculosis, AIDS,

syphilis, rheumatic fever following streptococcal infections, herpes

• Non-communicable 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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Agent Environment

Host

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 10-15 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

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


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


• 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


• 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 SHOWINGDISEASE PREVENTION AND CONTROL STRATEGIES

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DISEASE AND INJURY PREVENTIONAND 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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PowerPoint slide]

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 well-functioning 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


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


• 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


• 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


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


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.)


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


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.)

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CLASSIFYING DISEASES w Acute Diseases Acute diseases are those conditions in which the peak severity of symptoms occurs within three months (usually sooner),