Infectious Diseases Flashcards
Define outbreak
= Localized disease epidemic (e.g., in a town or healthcare facility)
Define pandemic
an epidemic on a worldwide scale (e.g., 1918 flu)
Define epidemic
Excessive occurrence of disease (vs. usual frequency)
Define communicable/infectious disease
= Illness caused by infectious agent that can be transmitted from one person to another (what do we mean by transmitted?)
Define epidemic threshold
minimum number of cases (or deaths) that would support the conclusion than an epidemic was underway, based on statistical projections and expectations of usual frequency
NEED DATA ON USUAL OCCURRENCE OF DISEASE TO KNOW IF IT’S AN EPIDEMIC
Yes…
Define agent
the cause of the disease
define host
an organism, usually a human or animal that harbors a disease
define environment
is those surroundings and conditions external to the human or animal that cause or allow disease transmission
What are three major factors in the pathogenesis of disease, FUNDAMENTAL PUBLIC HEALTH CONCEPTION OF DISEASE CAUSALITY
well-suited to explaining etiology of infectious disease; ALSO IMPORTANT FOR UNDERSTANDING METHODS FOR INVESTIGATION AND CONTROL OF EPIDEMICS
Diseases do not occur in a vacuum, virtually all result from some interaction between host, agent and environment.
And even though some diseases are genetic in nature, even the presentation of these depends on interaction between genetic and environmental conditions.
Many of the underlying principles re: disease transmission are most clearly demonstrated using infectious disease model
Shows the interaction and interdependence of agent, host, environment, and time as used in the investigation of diseases and epidemics.
What is pathogenicity and high low
high pathogenicity means it causes disease in almost everybody, low it causes a disease but it doesn’t impact you as much, most people have subclinical levels, you can be affected by it but it doesn’t show, you are exposed to polio but you won’t get it.
-Capacity of the agent to cause overt disease in the infected host
-High pathogenicity (few subclinical cases): measles
-Low pathogenicity (most cases are subclinical): polio
= number of individuals with clinically apparent disease / number exposed to an infection
what CHARACTERISTICS INFLUENCE WHEN AN INFECTIOUS DISEASE AGENT WILL BE TRANSMITTED TO A AHOST, WHETHER ITWILL PRODUCE DISEASE, THE SEVERITY OF DISEASE AND THE OUTCOME OF INFECTION?
- toxigenicity
- resistance
- antigenicity
Define resistance
-ability of agent to survive adverse environmental conditions. The flu: conditions need to be exactly right for the flue to exists, anthrax is highly resistant bc they can be in the ground for years, hepatitis
Define toxigenicity
the ability of the agent to produce a toxin or poison
ex: shellfish poisoning
Define antigenicity
- the ability of an agent to produce antibody production in a host, a disease with high antigenicity is a disease that you get and you are not worried about getting again because it caused a high antibody reaction in the body
- Related to immunogenicity = infection’s ability to produce specific immunity
- Some agents induce long-term immunity against infection, e.g., reinfection with measles is rare
Define infectivity and give examples
-what do i need to do in order to transmit a disease, how easy is it to transmit a disease
-Capacity of an agent to enter and multiply in a susceptible host and produce infection or disease
-Measured by the secondary attack rate
Ex: polio and measles have high infectivity rate
Define virulence
-what is it going to do to you? is it going to kill you?
-Agent’s capacity to induce disease in the host
Sometimes used as a synonym for pathogenicity
= number of total cases with overt infection / total number of infected cases.
If fatal, use case fatality rate (CFR)
Rabies virus is extremely virulent, high CFR
Define vector
An organism that transports disease
An agent infects a host: true or false?
True
What are the two types of defense mechanisms?
- nonspecific: reduce likelihood an agent will penetrate body and cause disease, variable by host
- Disease specific: immunity (resistance_ against a particular agent –two types: natural + artificial
Examples of nonspecific defense mechanisms
skin, mucosal surfaces, tears, saliva, gastric juices, immune system
What is active immunity?
Disease organism stimulates the potential host’s immune system to create antibodies against the disease
Long lasting, but requires time to develop
What are the two types of passive immunity?
natural and artifical
What is natural, passive immunity?
Short-term immunity provided by a preformed antibody
Ex: Preformed antibodies passed to fetus during pregnancy and breastfeeding through colostrum, Provide short-term immunity in newborn
What is natural, active immunity? Give an example
From infection by the agent
Ex: patient develops long-term immunity to chickenpox from a naturally acquired infection
what is artificial, passive immunity?
Preformed antibodies given to exposed individuals to confer protection against disease
Example: Prophylaxis against hepatitis by administration of immune globulin to individuals who have been exposed
what is artificial, active immunity?
Artificial, active or vaccine-induced immunity
From injection with vaccine that stimulates antibody production in host (immunologic response)
Response mimics natural infection with little or no risk to patient
What is direct transmission?
person to person contact
exx: STD’s
What is indirect transmission?
-SPREAD THROUGH AN INTERMEDIARY SOURCE, E.G., VEHICLES, FOMITE (DOORKNOB), VECTORS (MOSQUITO)
What is portal of exit?
- sites where infectious agent may leave the body, e.g., respiratory passages, the alimentary canal, and the openings in the genitourinary system, and skin lesions.
- Agent must exit in large enough quantities to survive in the environment and overcome the defenses at the portal of entry into the host.
what is the portal of entry?
locus of access to the human body, e.g., mouth and digestive system and the mucous membranes or wounds in the skin.
Incubation period
- Infectious organism replicates within host
- Time interval between exposure to infectious agent and appearance of first signs of disease
- Applies to clinically apparent cases of disease
- Provides a clue to the time and circumstance of exposure to the agent, type of agent
What is herd immunity?
- Immunity of a population, group, or community against an infectious disease when a large proportion of individuals are immune either through vaccinations or prior infection
- Confers protection even though not all individuals in the population have been immunized
- Requirement differ by disease
Not all exposures lead to illness…what is colonization and infestation?
Colonization
–Agents multiply on surface of the body without invoking tissue or immune response
Infestation
–Presence of living infectious agent on body’s exterior surface, upon which a local reaction may be invoked
What is inapparent infection?
Subclinical infection with no clinically obvious symptoms of infection present
- -Subclinical infection
- -Disease can still be transmitted
- -Use serologic evidence of infection
Example: Increase in antibodies and enzymes in patients with hepatitis A virus
In asymptomatic individuals, clinicians can look for serologic evidence of infection
Look at iceberg concept of infection
slide 31
*MOST INFECTIONS ARE SUBCLINICAL AND IN A SUBSTANTIAL NUMBER OF EXPOSURES TO A DISEASE AGENT MAY NOT PRODUCE ANY INFECTION OR CELL ENTRY
What are the three measures related to disease outbreaks
Attack rate
Case fatality rate
Basic reproductive rate
What is attack rate?
- Proportion of a group that experiences the outcome under study over a given period
- Used for acute health events
- Attack rate = sick / (sick + well exposed) * 100 during a certain time period
- Can help us identify cause of outbreak (comparing attack rates for those who did and did not eat food, going through list – the one with biggest difference prob the cause)
What is case fatality rate?
How virulent is the disease?
Number of deaths due to disease “X”/Number of cases of disease “X”*100
What is a mortality rate?
-a measureofthe numberof deaths(in general, or due to a specific cause)in apopulation, scaled to the sizeof that population, per unitoftime
What is basic reproductive rate?
Number of infections produced on average by an infected individual
Used as measure of transmissibility of disease
Affected by:
Duration of infectivity
Infectiousness of the organism
Number of susceptible people with whom the infected patient comes in contact
What is the formula for reproductive rate?
R0 = C x P x D
C = the number of contacts the infectious person makes per unit time (day, week, month, etc.)
P = probability of transmission per contact with the infectious person
D = the duration that the infected person is infectious to others
In general, f R0>1, disease will continue to spread; if R0<1, disease will eventually disappear from population
