L2: General Epidemiology of Communicable Diseases Flashcards
Def of Infection
Entry, development &/or multiplication of the infectious agent in the body of man or animal.
Depending on factors in both host and organism; Infection results into either:
- A clinically manifest disease (Infectious disease). Or
- The presence of infection without recognizable clinical signs or symptoms and identifiable only by laboratory means (Inapparent infection-subclinical infection).
Def of Infestation
The lodgment, development and reproduction of a parasite on the body surface or inside body tissues
Def of Contamination
The presence of an infectious agent on a body surface, in clothes, bedding, toys, surgical instruments or dressings, or other inanimate articles or substances including water and food.
Def of Communicable disease
- An illness due to a specific infectious agent or its toxins that arises through transmission from an infected person, animal or inanimate reservoir to a susceptible host.
- It may be either directly or indirectly
Def of Latent Infection
- Infectious agent lies “dormant” within the host without clinical manifestations.
- It reactivates under certain conditions causing the disease.
Ex of agents with Latent Period
herpes zoster, Pulmonary tuberculosis
Def of Opportunistic infection
Nonpathogenic agents, cause disease when host immunity decreased
Examples of Opportunistic infection
Pneumocystis carinii, Toxoplasma, CMV
Def of Zoonotic infection
- An infection or infectious disease transmissible under natural conditions from vertebrate animals to humans
what is World Health Organization (WHO)?
- A part of the United Nations that deals with major health issues around the world.
- The World Health Organization sets standards for disease control, health care, and medicines; Conducts education and research programs; and publishes scientific papers and reports.
- The headquarters are located in Geneva, Switzerland.
WHO Regions
International Health Regulations (IHR)
Public health Emergency of International Concern (PHEIC)
The WHO should be notified if …….
Types of occurrences and spread (distribution) of infectious diseases in communities
- Sporadic
- Cluster
- Endemic
- Epidemic
- Outbreak
- Pandemic
Sporadic Spread
The infrequent and irregular occurrence of a disease (without common source of infection)
Cluster Spread
The aggregation of cases grouped in place and time.
Endemic Spread
- The constant presence of an infectious disease within a given geographic area.
- It may also refer to the usual prevalence (baseline level) of a given disease within such area
Endemicity of a disease is determined by ……
the existence of its ecological factors (agent, host and environment)
Epidemic
- An increase in the number of cases of a disease above what is normally expected in that population in that area.
- The number of cases indicating epidemic varies according to the infectious agent, size and type of population and time and place of occurrence.
Epidemic threshold
- The critical number or incidence above which an urgent measure is required to control the emerging epidemic.
- Each disease has a specific threshold that depends on its infectivity, transmissibility and the degree of endemicity in a locality.
Outbreak
Epidemic in limited geographic area or confined group.
Pandemic
Epidemic that spreads over several countries or continents (Epidemic that crosses international borders)
trends of occurrence of infectious diseases
The occurrence of disease changes over time, Some of these changes occur regularly, while others are unpredictable.
Epidemics, outbreaks or pandemics occur when
Secular trends
Some diseases show long term variation in the occurrence.
Seasonal trend
- Some diseases such as influenza and West Nile infection are known to have characteristic seasonal distributions.
- Seasonal patterns may suggest hypotheses about how the infection is transmitted, what behavioral factors increase risk, and other possible contributors to the disease or condition.
Day of week and time of day trend
In conditions related to occupational or environmental exposures that tend to occur at regularly scheduled intervals.
Epidemiologic weeks
Natural History of Disease
It is the progress of a disease in an individual over time in absence of intervention.
The outcome of any infection depends on two opposing forces:
- Invading organism: Dose, pathogenicity, virulence.
- The host: Body resistance and immunity.
Chain of infection (infectious cycle)
Def of Infectious agent
An organism (virus, bacteria, fungus, protozoa or helminth) that is capable of producing infection or infectious disease.
Agent factors that affect disease behavior
- Infectivity
- Pathogenicity
- Virulence
- Antigenicity (Immunogenicity)
- Resistance
what is Infectivity?
Ability of agent to produce infection (invade, survive and multiply) in a susceptible host
What is Infectivity measured by?
- Measured by the secondary attack rate (Proportion of exposed susceptible who become infected).
- Secondary attack rate = (Number of secondary cases ÷ Number of exposed susceptible) x 100.
what is Pathogenecity?
- Ability of the organism to produce overt clinical reaction after infection.
What is Pathogenecity Measured by?
- Measured by the ratio of clinical to subclinical case.
What is Virulence?
- The degree of pathogenicity of an infectious agent.
What is Virulence measured by?
- Ability of organism to produce severe pathological reaction (death or irreversible damage).
- Measured by case fatality rates.
- Case fatality rate = (Total number of deaths from a disease / Total number of cases of that diseases) X 100.
What is Antigenicity (Immunogenicity)?
- Ability of organism to produce specific immunity (antibodies).
- Measured by rate of occurrence of a second attack.(Re infection).
What is Resistance of an agent?
The ability of the agent to survive adverse environmental conditions.
Environmental resistance of Agents
