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Prevention & Control of Infectious Diseases 

Dr. Anmar Aldewachi M.B.Ch.B MD MPH JHSFM

Definitions

Infectious disease A clinically manifested disease of human or animal resulting from infection. Infected individual A person or animal ,that harbors an infectious agent & who has either manifest disease or in apparent infection .

Definitions

Infectivity : The ability of the infectious agent to enter, survive & multiply in the host. Infectiousness: The relative ease with which an infectious agent is transmitted to other hosts.

Definitions

Infection: The entry & development or multiplication of an infectious agent in the body of persons or animals. In apparent infection presence of infection in host without recognizable clinical signs or symptoms.

Definitions

Incubation period The time interval between initial contact with an infectious agent & the first appearance of symptoms associated with the infection . Extrinsic incubation period In vector ,it is the time between entrance of an organism into the vector & the time when that vector can transmit the infection

Definitions

Prepatent period The period between the time of exposure to an infectious agent &time when the agent can be detected in blood or stool.


Definitions
Period of communicability Is the time during which an infectious agent may be transmitted directly or indirectly from an infected person to another, from infected animal to humans, or from infected person to animals.

Chain of infection

Source or reservoir
Mode of transmission
Susceptible host

Reservoir

Any person ,animal ,arthropod ,plant, soil ,or substance (or combination of these) in which an infectious agent normally lives & multiplies ,on which it depends primarily for survival, & where it reproduces itself in such manner that it can be transmitted to a susceptible host .

Reservoir

Reservoir is of three types Human reservoir Animal reservoir Reservoir in non-living things

Carrier

A person or animal that harbors a specific infectious agent without clinical disease & serves as a potential source of infection. As a rule carriers are less infectious than cases but more dangerous ,because they remain hidden and readily infect susceptible individual.

Carrier

Elements of carrier state: Disease agent is presents in the host Absence of signs and symptoms Shedding of disease agent in discharge and excretion and act as source of infection to others


Carrier
Carrier state classified as below Type Incubatory carriers: those who shed the infectious agent duration incubation period Convalescent carriers: those who continue shedding infectious agent duration convalescent period. Healthy carriers: victims of subclinical infection and develop carrier state.

Duration Temporary 6-12 months. Chronic more than 12 months Permanent for life Portal of exit Respiratory, urinary, intestinal, others

Mode of Transmission

Direct Physical contact Droplet Trans placental

Mode of Transmission

II. IndirectVehicle (Water, Milk ,Blood, Surgical instruments…….etc).InsectAir (droplet nuclei)SoilIII. Both

Prevention and control of infectious diseases

Prevention and Control Standard Measures
Hand hygiene Use of personal protective equipment Promotion of safe injection practices Handling and disposal of sharp equipments and materials

Prevention and Control Standard Precautions

Waste management Cleansing, disinfection and sterilization of patient care equipments. Isolation measures Use of aseptic techniques


Principles of control
Control of reservoir
Control of mode of transmission
Control of susceptible host

Control of reservoir

Recognition Clinical signs& symptoms Laboratory investigation Notification. Isolation (period of communicability)

Control of reservoir

Treatment Disinfection Quarantine

Control of mode of transmission

Major aspect of communicable disease control is to break the chain of transmission . ExamplesChlorination of water to control diseases like typhoid, hepatitis A, cholera…….etcControl of breeding places of mosquito in case of malariaEnvironmental control (proper sewage disposal)

Control of susceptible host

Active immunization Passive immunization Chemoprophylaxis Cholera Diphtheria Meningitis Malaria

Epidemic measures

Procedures of an emergency character designed to limit the spread of communicable disease that has developed widely in a group or community, or within area, state or nation.

International measures

interventions designed to protect population against the known risk of infection from international source.

Isolation

Applied to the patient , represent separation for a period of communicability of infected person, from others in such places & under such conditions as to prevent or limit the spread to those who are susceptible to the disease .

Isolation

Strict isolation Highly infectious disease. Spread by air & contact. Use of mask, gowns& gloves for all persons entering the room. Private room. Special ventilation device.

Isolation

Contact isolation Less highly transmissible disease. Transmitted by close or direct contact. Private room for more than one patient infected with the same organism. Mask for those who come in close to patient . Gown & gloves if soiling is likely.

Isolation Respiratory isolation To prevent transmission of infectious disease over short distance by air. Private room is indicated. Pt with the same organism may share. Masks for those who are in close contact. Gowns & gloves are not indicated.

Isolation T.B isolation for patients with active pulmonary T.B. Private room with special ventilation & closed door. Those entering the room must use respiratory masks. The use of gowns will prevent gross contamination of clothing . Gloves are not indicated.

Isolation Enteric precautions Applied for infections transmitted by direct or indirect contact with feces . Use of private room if patient hygiene is poor. Masks are not indicated . Gowns should be used if soiling is likely. Gloves used when touching contaminated materials .

Disinfection

Killing of infectious agents outside the body by direct exposure to chemical or physical agents.

Types

Concurrent disinfection Application of disinfection measures as soon as possible after discharge of infectious material from the body of an infected person or after soiling of articles with such infectious discharges.

Types

Terminal disinfection Application of disinfection measures after the patient has been removed by death or to the hospital or he has ceased to be a source of infection or after hospital isolation.

Quarantine

Restriction of activities of well person or animals who have been exposed to case of communicable disease during its period of communicability to prevent disease transmission during incubation period.

Personal Surveillance

Close medical observation of contacts to permit prompt recognition of infection or illness but without limitation of movement

Complete or Absolute Quarantine

The limitation of freedom of movement of those exposed to the communicable disease for period of time not longer than the longest incubation period of that disease ,in such manner as to prevent effective contact with those not exposed.



Modified QUARANTINE Partial limitation of freedom of movement of contact e.g. exclusion of children from school

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