Infectious Diseases

Question 1

Define outbreak

Answer 1

= Localized disease epidemic (e.g., in a town or healthcare facility)

Question 2

Define pandemic

Answer 2

an epidemic on a worldwide scale (e.g., 1918 flu)

Question 3

Define epidemic

Answer 3

Excessive occurrence of disease (vs. usual frequency)

Question 4

Define communicable/infectious disease

Answer 4

= Illness caused by infectious agent that can be transmitted from one person to another (what do we mean by transmitted?)

Question 5

Define epidemic threshold

Answer 5

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

Question 6

NEED DATA ON USUAL OCCURRENCE OF DISEASE TO KNOW IF IT’S AN EPIDEMIC

Answer 6

Yes…

Question 7

Define agent

Answer 7

the cause of the disease

Question 8

define host

Answer 8

an organism, usually a human or animal that harbors a disease

Question 9

define environment

Answer 9

is those surroundings and conditions external to the human or animal that cause or allow disease transmission

Question 10

What are three major factors in the pathogenesis of disease, FUNDAMENTAL PUBLIC HEALTH CONCEPTION OF DISEASE CAUSALITY

Answer 10

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.

Question 11

What is pathogenicity and high low

Answer 11

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

Question 12

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?

Answer 12

1. toxigenicity
2. resistance
3. antigenicity

Question 13

Define resistance

Answer 13

-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

Question 14

Define toxigenicity

Answer 14

the ability of the agent to produce a toxin or poison

ex: shellfish poisoning

Question 15

Define antigenicity

Answer 15

• 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

Question 16

Define infectivity and give examples

Answer 16

-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

Question 17

Define virulence

Answer 17

-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

Question 18

Define vector

Answer 18

An organism that transports disease

Question 19

An agent infects a host: true or false?

Answer 19

True

Question 20

What are the two types of defense mechanisms?

Answer 20

1. nonspecific: reduce likelihood an agent will penetrate body and cause disease, variable by host
2. Disease specific: immunity (resistance_ against a particular agent –two types: natural + artificial

Question 21

Examples of nonspecific defense mechanisms

Answer 21

skin, mucosal surfaces, tears, saliva, gastric juices, immune system

Question 22

What is active immunity?

Answer 22

Disease organism stimulates the potential host’s immune system to create antibodies against the disease
Long lasting, but requires time to develop

Question 23

What are the two types of passive immunity?

Answer 23

natural and artifical

Question 24

What is natural, passive immunity?

Answer 24

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

Question 25

What is natural, active immunity? Give an example

Answer 25

From infection by the agent | Ex: patient develops long-term immunity to chickenpox from a naturally acquired infection

Question 26

what is artificial, passive immunity?

Answer 26

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

Question 27

what is artificial, active immunity?

Answer 27

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

Question 28

What is direct transmission?

Answer 28

person to person contact | exx: STD's

Question 29

What is indirect transmission?

Answer 29

-SPREAD THROUGH AN INTERMEDIARY SOURCE, E.G., VEHICLES, FOMITE (DOORKNOB), VECTORS (MOSQUITO)

Question 30

What is portal of exit?

Answer 30

- 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.

Question 31

what is the portal of entry?

Answer 31

locus of access to the human body, e.g., mouth and digestive system and the mucous membranes or wounds in the skin.

Question 32

Incubation period

Answer 32

- 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

Question 33

What is herd immunity?

Answer 33

- 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

Question 34

Not all exposures lead to illness...what is colonization and infestation?

Answer 34

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

Question 35

What is inapparent infection?

Answer 35

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

Question 36

Look at iceberg concept of infection

Answer 36

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

Question 37

What are the three measures related to disease outbreaks

Answer 37

Attack rate Case fatality rate Basic reproductive rate

Question 38

What is attack rate?

Answer 38

- 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)

Question 39

What is case fatality rate?

Answer 39

How virulent is the disease? | Number of deaths due to disease “X”/Number of cases of disease “X”*100

Question 40

What is a mortality rate?

Answer 40

-a measure of the number of deaths (in general, or due to a specific cause) in a population, scaled to the size of that population, per unit of time

Question 41

What is basic reproductive rate?

Answer 41

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

Question 42

What is the formula for reproductive rate?

Answer 42

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