PU520: Principles of Epidemiology Unit 7 Infectious Disease and Outbreak Investigation Flashcards
(40 cards)
What is defined as a disease due to an infectious agent? Such agents include bacteria and viruses.
Infectious disease
What is a disease transmitted by direct or indirect contact with a host that is the source of the pathogenic agent?
Contagious disease
What is an illness due to a specific infectious agent or its toxic products that arises through transmission of such agent or products from an infected person, animal, or reservoir to a susceptible host, either directly or indirectly through an intermediate plant or animal host, vector, or the inanimate environment?
Communicable disease
Some writers use the terms infectious disease and communicable dis-ease as synonyms. Technically speaking, these terms can have different meanings.
What is an infection caused by a parasite, which “… is an animal or vegetable organism that lives on or in another and derives its nourishment therefrom.”?
Parasitic disease
What is a defined as the entry and development or multiplication or an infectious agent in the body or persons or animals?
Infection
What is the epidemiologic triangle?
It includes three major factors - agent, host, and environment - and is one of the longstanding models used to describe the etiology of infectious diseases.
Although this model has been applied to the field of infectious disease epidemiology, it also provides a frame-work for organizing the causality of some other types of health outcomes, such as those associated with the environment.
Considering the epidemiologic triangle, what is an agent?
An agent refers to “[a] factor (e.g., a microorganism, chemical substance, form of radiation, mechanical, behavioral, social agent or process) whose presence, excessive presence, or (in deficiency diseases) relative absence is essential for the occurrence of a disease.
A disease may have a single agent, a number of independent alternative agents (at least one of which must be present), or a complex of two or more factors whose combined presence is essential for or contributes to the development of the disease or other outcome.
Considering the epidemiologic triangle, what is the term environment?
The term environment is defined as the domain in which disease-causing agents may exist, survive, or originate; it consists of all that which is external to the individual human host.
Considering the epidemiologic triangle, what is a host?
The host is [a] person or other living animal, including birds and arthropods, that affords subsistence or lodgment to an infectious agent under natural conditions.
A human host is a person who is afflicted with a disease; or, from the epidemiologic perspective, the term host denotes an affected group or population.
What does infectivity refer to?
It refers to the capacity of an agent to enter and multiply in a susceptible host and thus produce infection or disease.
What does the term virulence refer to?
It refers to the severity of the disease product (i.e., whether the disease has severe clinical manifestations or is fatal in a large number of cases)
What is a toxin?
It usually refers to a toxic substance (a material that is harmful to biologic systems) made by living organisms.
Foodborne intoxications are examples of illness caused by the actions of microbial toxins.
What is a host characteristic that can limit the ability of an infectious disease agent to produce infection?
Immunity
This refers to the host’s ability to resist infection by an agent. This status is usually associated with the presence of antibodies or cells having a specific action on the microorganism concerned with a particular infectious disease or on its toxin.
What is the difference between active and passive immunity?
Active immunity refers to the immunity that the host has developed as a result of natural infection with a microbial agent. This can also be used to describe immunity gained by an injection of a vaccine (immunization) that contains an antigen (a substance that stimulates antibody formation).
Examples of antigens are live or attenuated microbial agents. (Jenner’s development of an immunization against smallpox was an early example of using a vaccination to protect against a disease.)
Active immunity is usually of long duration and is measured in years.
Passive immunity refers to the immunity that is acquired from antibodies produced by another person or animal.
For instance, the newborn infant’s natural immunity conferred trans-placentally from its mother. Another example is artificial immunity that is conferred by injections of antibodies contained in immune serums from animals or humans. Passive immunity is of short duration, lasting from a few days to several months.
What does herd immunity mean?
Denotes the resistance (opposite of susceptibility) of an entire community to an infectious agent as a result of the immunity of a large proportion of individuals in that community to the agent.
Herd immunity can limit epidemics in the population even when not every member of the population has been vaccinated.
A clinically apparent disease is one that produces observable clinical signs and symptoms. What does the term incubation period denote?
What terms may be used when the infection does not show obvious clinical signs or symptoms?
This term refers to the time interval between invasion by an infectious agent and the appearance of the first sign or symptom of the disease.
Subclinical, also called inapparent.
For example, hepatitis A infections among children and the early phases of infection with HIV are largely asymptomatic. Nevertheless, individuals who have inapparent infections can transmit them to others; thus inapparent infections are epidemiologically significant and part of the spectrum of infection.
What is the term generation time mean?
It is defined as the time interval between lodgment of an infectious agent in a host and the maximal communicability of the host.
The generation time for an infectious disease and the incubation time may or may not be equivalent.
For some diseases, the period of maximal communicability precedes the development of active symptoms. Incubation period applies only to clinically apparent cases of disease, whereas generation time applies to both inapparent and apparent cases of disease.
What is a person or animal that harbors a specific infectious agent without discernible clinical disease and that serves as a potential source of infection?
What would you call if this host’s status is lonstanding?
A carrier or referred to as carrier status.
A chronic carrier.
Example:
“Typhoid Mary” Mallon, who worked as a cook in New York City during the early 1900s and was alleged to be a typhoid car-rier. Several cases of typhoid fever were traced to households where she was employed. Typhoid fever, caused by Salmonella bacteria (S. typhi), is a systemic infection associated with a 10 to 20% case fatality rate when untreated. After the first cases of typhoid were associated with her, Mallon was quarantined for 3 years on Brother Island in New York City and then released with the proviso that she no longer work as a cook.
What is the difference between quarantine and isolation?
Quarantine—Well persons who have been exposed to an infectious disease are prevented from interacting with those not exposed, for example, preventing medical personnel who have been exposed to Ebola virus from leaving their place of residence. This is different from isolation.
Isolation—Persons who have a communicable disease are kept away from other persons for a period of time that corresponds generally to the interval when the disease is communicable, for example, maintaining isolation of patients with Ebola in special isolation units.
What term is used in an epidemiologic investigation of a disease outbreak to denote the first case of a disease to come to the attention of authorities?
Index case
What are some examples of how environmental determinates may act as potential influences associated with the occurrence of diseases and other health outcomes? (4 main categories/examples)
Physical environment - The availability of clean and abundant water supplies is instrumental in maintaining optimal sanitary conditions; waterborne diseases such as cholera are associated with pathogens that can contaminate water. Other pathogens such as fungi may be present naturally in the soil in some geo-graphic areas. An example is the fungus Coccidioides immitis, found in California’s San Joaquin Valley. This fungus is the agent for San Joaquin Valley fever.
Climatologic environment - In warm, moist, tropical climates, disease agents and arthropod vectors such as the Anopheles mosquito, the vector for malaria, are able to survive and cause human and animal diseases. These same vectors and the diseases associated with them are not as common in drier, colder, temperate climates. However, with global warming observed in recent years, it may be possible for disease vectors to migrate to regions that formerly were much colder.
Biologic environment - The biologic environment includes the presence of available plant and animal species that can act as reservoirs for disease agents. These species may be part of the cycle of reproduction of the disease agent. An example is the disease schistosomiasis, which depends on the presence of intermediate hosts (certain species of snails) in order to reproduce. Schistosomiasis, a major cause of illnesses including liver cirrhosis, is found in Africa, the Middle East, parts of South America and Asia, as well as some other geographic areas.
Social and economic environment - While the world becomes increasingly urbanized as inhabitants search for improved opportunities, cities will become ever more crowded. The overcrowded urban environment can contribute to the spread of infections through person-to-person contact and creation of unsanitary conditions such as improper disposal of human wastes.
What do you call an infectious disease that is habitually present in an environment (either a geographic or population group)?
It is said to be endemic.
Plague is an endemic among certain species of rodents in the western United States.
What is another term to describe the presence of an infectious agent in the environment which is a place where infectious agents normally live and multiply?
This place can be human beings, insects, soils, or plants.
Reservoir
