Epidemiology of Infectious Diseases
What is infectious disease epidemiology used for?
Identification of causes of new, emerging infections.
Surveillence of infectious disease
Identification of source of outbreaks
Studies of routes of transmission and natural history of infections
Identification of new interventions
Infection : the entery & development or multiplication of an infectious agent in the body of persons or animals.
Infectious agent: an organism (virus, rickettsia, bacteria, fungus, protozon or helimentheses) that is capable of producing infection .
Infectivity: expresses the ability of diseses agent to enter, survive & multiply in the host.
Infectious disese: a clinically manifest disease of humen or animals resulting from an infection
Incubation period: the time interval between initial contact with an infectious agent & the first apparent of the symptoms associated with the infection. In a vector, it is the time between entrance of an organism into the vector & the time when that the vector can transmit the infection (extrinsic incubation period). The period in people between the time of exposure to a parasite & the time when the parasite can be detected in blood or stool is called the prepatent period.
Contact: a person or animal that has been in such association with an infected person or animal or a contaminated environment as to have had an opportunity to acquire the infection. Herd immunity: the immunity of a group or community. The resistance of a group to invasion & spread of an infectious agent, based on the resistance to infection of ahigh proportion of individual member of the group. Isolation: as applied to patients, isolation represent separation, for the period of communicability, of infected persons or animals from others in such places & under such conditions as to prevent or limit the direct or indirect transmission of the infectious agents from those infected to those who are susceptible to infection or who may spread the agent to others.
Quarantine: restriction of the activities of well persons or animals that have been exposed to a case of communicable disease during its period of communicability (i.e. contacts) to prevent disease transmission during the incubation period if infection should occur. Host: a person or other living animal that affords lodgment of an infectious agent under natural conditions. Hosts in which the parasite attains maturity or passes its sexual stage are primarily or definitive hosts. Those in which the parasite is in a larval or asexual stage are secondary or intermediate hosts. A transport host is a carrier in which the organism remains a live but dose not undergoes development. Reservoir: (of infectious agents) 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 it self in such manner that it can be transmitted to a susceptible host.
Mode of transmit ion: describes the mechanisms by which an infectious agent is spread to human. Such mechanism include direct, indirect, airborne. Period of communicability: is the time (days, weeks or months) during which an infectious agent may be transmitted, directly or indirectly, from an infected person to another person, from infected animals to humans, or from an infected person to animal or arthropod.
Transmission
Cases
Index – the first case identified
Primary – the case that brings the infection into a population
Secondary – infected by a primary case
Tertiary – infected by a secondary case
Predisposition to Infections
(Host Factors)
Gender
Genetics
Climate and Weather
Nutrition, Stress, Sleep
Smoking
Stomach Acidity
Hygiene
Ecological Factors in Infections
Altered environment
{Air conditioning}
Changes in food production & handling
{intensive husbandry with antibiotic protection; deep-freeze; fast food industry}
Climate changes
{Global warming}
Deforestation
Ownership of (exotic) pets
Air travel & Exotic journeys / Global movements
Increased use of immunosuppressives/ antibiotics
Endemic
Transmission occur, but the number of cases remains constant
Epidemic
The number of cases increases
Pandemic
When epidemics occur at several continents – global epidemic
Sporadic level: occasional cases occurring at irregular intervals
Endemic level: persistent occurrence with a low to moderate level
Hyperendemic level: persistently high level of occurrence
Epidemic or outbreak: occurrence clearly in excess of the expected level for a given time period
Pandemic: epidemic spread over several countries or continents, affecting a large number of people