Unit 1: Principles of Epidemiology Flashcards
How is the term “host “defined?
As a living person or animal that is harboring a disease agent
How is the term “carrier” defined?
As a person or animal that harbors a disease agent but has no clinical signs of the disease
How is a primary (definitive) host defined as?
Agent attains its maturity and goes through its sexual or reproductive stage
How is a secondary (intermediate) host defined as?
Agent is in its larval stages
What are infectious disease agents?
Organisms that live on or in the body of a host and can produce disease or illness
What is infectivity?
The ability of the agent to invade and multiply, or to produce infection in the host
What is pathogenicity?
The ability of an agent to produce clinical disease in a host
What is virulence?
The proportion of clinical cases resulting in severe clinical manifestations
Which agent type are multicellular organisms, often referred to as parasites and are capable of causing disease in both animals and humans?
Metazoa
Which agent type are single-celled, animal-like organisms? Most are free-living and found in soil and water.
Protozoa
What are the two forms of fungi?
Single cell (yeast)
Multicellular (molds)
What are the three shapes bacteria can be found in?
Bacillus (rod)
Coccus (sphere)
Spirillum (spiral)
Which agent type are small bacteria, obligate, and intracellular parasites?
Rickettsia
Which agent type are particles of nucleic acid, highly infectious, and cause common diseases?
Viruses
When a host is exposed to a disease agent, what are the three possible outcomes?
- Nowhere to lodge—agent unable to penetrate a host’s body or unable to stay in host’s body
- No effect—agent may enter a host’s body but not cause signs and symptoms
- Great effect—agent may invade a host’s body, multiply, and cause signs and symptoms of disease
What are the three main modes of entry used by disease agents to enter the body?
Ingestion
Inhalation
Penetration
What are the three parts to a chain of infection?
Source or reservoir, mode of transmission, and a susceptible person or host
What may serve as a source of infection?
Person
Animal
Inanimate object
Substance
What are the two ways direct transmission can occur?
Direct contact
Contact with droplets
What are the three ways indirect transmission can occur?
Vehicleborne
Vectorborne
Airborne transmission
What are the two categories under vectorborne transmission?
Mechanical
Biological
What term is used to describe a person who is actually ill with a disease?
Case
What term is used to describe a person who harbors disease organisms, but is not ill?
Carrier
What is the most effective way to prevent and/or control disease?
Break the chain of infection
What are the measures to control or prevent infection at the source?
Diagnosis and treatment
Isolation
Destruction of the source
Education
How does the skin and mucous membranes protect the body?
By providing a protective covering against living organisms and many chemicals
What are three protective structures that help the body against physical forces and aid in thermal regulation?
Hair
Sweat glands
Fat pads
How is the abdominal cavity designed to protect the vital organs?
It is well lubricated so the organs will slide out of line with direct pressure and sharp objects
How does the respiratory tract protect itself?
When coughing or sneezing is initiated, and with the cilia’s constant beating to remove harmful substances
In what functional ways does the gastrointestinal tract protect the body?
By initiating vomiting and diarrhea to move unwanted objects out of the system
How does the body defend itself against living pathogens?
White blood cells attack and destroy pathogens at a site, causing inflammation, and are moved to the lymphatic system
How does the age of a population affect the occurrence of disease?
The very young have poorly developed immune systems, while the very old have defense systems that are starting to weaken
What are the three gender factors affecting the distribution of disease?
Anatomical differences
Hormonal factors
Exposure potential
What effect does an inadequate intake of nutrients have on the body?
There is less energy that can be used to produce antibodies and white blood cells
What effect does stress have on host defenses?
It does not allow the body’s defense system to work at its fullest
What are seven human behaviors that affect disease transmission?
1) Diet
2) Disposal of human wastes
3) Personal hygiene
4) Personal contact
5) Household hygiene
6) Occupation/recreation
7) Other behaviors
What are two physical environmental factors in the transmission of disease?
Climate and geography
What are two geographical features that can act as barriers or can aid the spread of disease?
Mountains and rivers
What factors are included in the social environment that affects the occurrence of disease?
Economic development, culture or customs, education level, public health services availability, and whether rural or urban
What term is used for conditions where the incidence in humans has increased within the past two decades or threatens to increase in the future?
emerging infectious diseases
Name three, military relevant, emerging infections that were previously unrecognized
Name any three:
(1) HIV.
(2) Lyme disease.
(3) Human ehrilichiosis.
(4) New influenza strains
In what settings have emerging and reemerging diseases plagued service members?
Training and operational deployments
What are some factors that contribute to the emergence or reemergence of diseases?
Urban decay, refugee migration, displaced persons, or poverty
What term is used to define numeric facts or data assembled, classified, and tabulated to present significant information about a given subject?
statistics
What term is used to define the number occurring most often in a group or set of numbers?
Mode
For the aerospace medicine report, you are asked to report the number of mosquitoes trapped and identified as medically important. Your counts of mosquitoes trapped each day for 13 days are 0, 0, 3, 6, 0, 9, 3, 6, 9, 11, 2, 0, and 60. What is the mean, mode, and median number of mosquitoes trapped over these 13 days?
Mean=8.3846
Mode=0 (occurs four times, others once)
Median=3
Calculate the mean, mode, and median using the data in question #2 above, except on day 13 use 600 for the daily count instead of 60
Mean=49.923
Mode=0
Median=3
Briefly describe the process for calculating the median of an array of numbers
Arrange the data from smallest to largest. Determine if you have an odd or even number of samples. If you have an odd number of samples, the median is the middle number; if you have an even number of samples, the median is the mean of the middle two numbers.
What term is used to measure the probability of occurrence of some particular event?
Rates
What is the formula to calculate rates?
= (X/Y) x K
What does the “X” represent in the rate formula
the number of times an event has occurred during a specific interval of time
What does the “Y” represent in the rate formula?
the number of persons exposed to the risk of the event during the interval
What does the “K” represent in the rate formula?
some power of 10
What term is used to define the temporary loss of manpower from duty?
Noneffectiveness
What term is defined as a daily rate that indicates the number of people not physically or mentally fit for duty
NER
What is the NER formula?
NER per 1,000 per day =
(Total days lost in period 1000) / (Average strength number of days in period)
With an average strength of 1,200, you lost 45 workdays during a 7-day period. What was your NER?
5.357
With an average strength of 2,400, you lost 38 workdays during a 30-day period. What was your NER?
0.52777
With an average annual (365 days) population of 5,200, you had 36 cases that lost workdays. What was your NER?
0.018967
With an average annual (365 days) population of 4,200 (average strength), you had 48 cases that lost workdays. What was your NER?
0.031
What term is used to define the number of new cases of a disease in a specific population over a period?
Incidence
What term is used to define the number of disease cases, old and new, occurring at a point of time?
Prevalence
Which type of rate is a measure indicating the frequency of new cases of a particular disease, or group of diseases, occurring in a population during a given period
Incidence rate (IR)
What is the incidence rate (IR) formula?
Incidence of disease X =
(Number of new cases occurring in a given period K) / (Population at risk in a given period)
With an average active duty population of 4,200 (average strength), you had 14 new cases of gonorrhea occurring within one month (30 days). What was your monthly IR?
3.33
What type of rate is applied to narrowly defined populations observed for limited periods, such as foodborne illness outbreaks or epidemics?
Attack rate (AR)
What is the Attack Rate (AR) formula?
Attack rate of disease X =
(number of cases 100) / (population at risk)
Ninety-six persons attended the base picnic—87 males and 9 females. There were 26 cases of staphylococcal food poisoning—19 males and 7 females. What was the AR?
27.08
Administering a vaccine or special duty to one group and withholding it from another group to determine its effect is an example of which kind of study method?
Experimental
Which study method are you using when nature provides the data for your investigation and you only observe, record, and state the result?
Observational
Which study method uses two similar populations or communities, except for the factor under observation
Controlled observation
Generally, which study method is used to trace the source of food poisoning outbreaks?
Uncontrolled observation
Which type of study design is used to look back in time to compare individuals with a disease to individuals without the disease to identify factors more common to the cases?
Retrospective
Which study method gets information about disease and other factors in a population at one point in time?
Cross-sectional survey
What are five purposes of an outbreak investigation?
(1) Control the outbreak if it is still occurring; (2) Identify the source, (3) mode of transmission, and (4) population at risk and (5) Identify measures to prevent future occurrences
What is an epidemic curve? Why is an epidemic curve constructed?
A graph of cases plotted according to time of onset of illness.
The curve is used to determine if the source is common, propagated (person-to-person), or both, and to identify the probable time of exposure
What is included in the epidemiological hypothesis when considering prevention and control measures?
Suspected causative agent, source of infection, means of transmission, and the population at risk
What three things help characterize data and identify patterns?
Time
Place
People
What is the 1st step to an outbreak investigation?
Prepare for field work
What is the 2nd step to an outbreak investigation?
Establish existence of an outbreak
What is the 3rd step to an outbreak investigation?
Take steps to establish or verify the diagnosis
What is the 4th step to an outbreak investigation?
Define and identify cases
What is the 5th step to an outbreak investigation?
Perform descriptive epidemiology
What is the 6th step to an outbreak investigation?
Develop a hypothesis
What is the 7th step to an outbreak investigation?
Evaluate hypothesis
What is the 8th step to an outbreak investigation?
Reconsider and refine your hypothesis
What is the 9th step to an outbreak investigation?
Implement prevention and control measures
What is the 10th step to an outbreak investigation?
Communicate your findings
