Infectious diseases

Prevention & Control of Infectious Diseases 

Dr. Anmar Aldewachi Ass.Prof. Of Family Medicine 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 inapparent infection . Infectivity : The ability of the infectious agent to enter, survive & multiply in the host.

Definitions

Infectiousness: The relative ease with which an infectious agent is transmitted to other hosts. Infection: The entry & development or multiplication of an infectious agent in the body of persons or animals. Inapparent 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 . 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 including arthropods.

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 is of three types Human reservoir (cases, carriers) 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

Carriers are classified as below Type Incubatory,convalescent,healthy Duration Transient few weeks Temporary 6-12 months Chronic more than year Permanent for life Portal of exit Respiratory,urinary,intestinal,others)

Mode of Transmission

I. Direct Physical contact Droplet (projection) Trans placental II. Indirect Vehicle (Water, Milk ,Blood, Eating utensils, Surgical instruments). Insect Air (droplet nuclei) III. Both

Prevention and control of infectious diseases

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

Control of reservoir

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

Control of mode of transmission :Chlorination 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 susciptible host:Active immunizationPassive immunizationChemoprophylaxis ( e.g meningitis, cholera)

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 . 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. 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.

Types of quarantine

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