MT2 > Basic Concepts in Epidemiology Flashcards
What definition describes the “incidence” of a disease?
The rate of development of a disease in a group over a period of time.
What definition describes the “prevalence” of a disease?
The number of people who have the disease at a certain point in time.
What is an example which uses the term “incidence” in relation to disease?
The incidence of myocardial infarction is about 1% per year in men aged 55-59 in our community.
What is an example which uses the term “prevalence” in relation to disease?
The presence of diarrhea in the children’s camp on July 13th was 33%.
What scale is used when talking about prevalence rates? What about incidence rates?
Prevalence: rates per 10,000
Incidence: rates per 100,000
For which 3 important notifiable diseases is the incidence rate higher in BC than the Canadian average?
- AIDS
- Hepatitis C
- Pertussis
For which 2 important notifiable diseases is the incidence rate lower in BC than the Canadian average?
- Gonococcal infections
2. Verotoxigenic E. coli
What definition describes the “morbidity” of a disease? Does it refer to prevalence or incidence?
The incidence of illness (disease) in a population. Includes both fatal and nonfatal at a point in time. Can refer to either prevalence or incidence.
What is an example which uses the term “morbidity” in relation to disease?
Morbidity rate of genital Chlamydia in Canada in 2000 was 32%.
What definition describes the “mortality” of a disease?
The incidence of death in a population.
What is an example which uses the term “mortality” in relation to disease?
The mortality rate varied from 25% to 33% of Europe’s population during plague epidemics in the middle ages.
What is meant by the term “Case Fatality Rate”?
An estimate of the number of deaths due to a disease based on the mortality rate of a small sample.
What is meant by a “sporadic” disease?
A disease which occurs only occasionally.
What is meant by a “endemic” disease?
A disease which is constantly present in a population.
What is meant by a “epidemic” disease?
A disease which is acquired by many people in a given area in a short time.
What is meant by a “pandemic” disease?
A worldwide epidemic.
What is meant by an “acute” disease?
A disease in which symptoms develop rapidly but the disease lasts only a short time.
What is meant by a “chronic” disease?
A disease in which symptoms develop slowly.
What is meant by a “subacute” disease?
A disease in which the severity is intermediate between acute and chronic.
What is meant by a “latent” disease?
A disease in which the causative agent is inactive for a time but then activates and produces symptoms.
What is meant by “herd immunity”?
Immunity in most of the population can prevent those with out immunity by limiting transmission of a disease.
What is meant by a “local” infection?
An infection in which the pathogen is limited to a small area of the body.
What is meant by a “systemic” (or “generalized”) infection?
An infection in which the pathogen has spread to the entire body.
What is meant by a “focal” infection?
A systemic infection which began as a local infection.
Define sepsis.
A toxic inflammatory condition arising from the spread of microbes from a focus of infection.
Define bacteremia.
Bacteria in the blood.
Define septicemia.
Aka: blood poisoning. The growth of bacteria in the blood.
Define toxemia.
Toxins in the blood.
Define viremia.
Viruses in the blood.
Define a primary infection.
An acute infection which causes the initial illness.
Define a secondary infection.
An opportunistic infection which follows a primary infection.
Define a subclinical disease.
An infection which produces no noticeable signs or symptoms.
List some predisposing factor which can in some cases make the body more susceptible to disease.
- Gender
- Inherited traits (ex: anemia)
- Climate and weather
- Fatigue
- Age
- Lifestyle
- Nutrition
- Chemotherapy
Describe the “incubation period” of a disease.
The interval between the initial infection and the first signs and symptoms.
Describe the “prodromal period” of a disease.
The short period after incubation in which the patient presents with early, mild symptoms.
Describe the “period of illness” of a disease.
The period during a disease’s progression in which the symptoms are most severe.
Describe the “period of decline” of a disease.
The period after maximum severity in which signs and symptoms subside.
Describe the “period of convalescence” of a disease.
The period at the very end of disease progression in which the body returns to its prediseased state.
What are the 3 main continual sources of infection?
- Human reservoirs (carriers)
- Animal reservoirs (zoonoses)
- Nonliving reservoirs
What term in used to describe a nonliving object capable of spreading disease via indirect contact transmission? Give an example.
A fomite. Objects which can harbour infection such as surgical devices, clothes, furniture, etc.
As per the definition, what is the distance cutoff for disease spread via droplet transmission?
<1 meter.
In what 3 ways can disease be transmitted via an inanimate reservoir?
- Waterborne
- Foodborne
- Airborne (dust, etc)
With regard to disease vectors, what differentiates mechanical transmission from biological transmission?
Mechanical: vector carries pathogen on its feet
Biological: pathogen reproduces in the vector and is transmitted vie bites or feces
What is another term used to describe a healthcare-associated infection? How many hospital patients are infected per year?
A nosocomial infection, which infects ~2 million patients per year (1 in 25). (~20,000 deaths).
What 3 factors play the greatest role in perpetuating healthcare-associated infections?
- Microorganisms in the hospital environment
- Weakened status of the host
- Chain of transmission in a hospital
What 3 factors most commonly compromise a person’s immunity in a hospital setting?
- Ongoing disease
- Therapy
- Burns
Describe an “emerging infectious disease”.
A disease which is new and either increasing in incidence or showing the potential to increase in incidence soon.
What are 3 common characteristics of emerging infectious diseases?
Most are:
- Zoonotic
- Viral in origin
- Vector-borne
What 8 main factors contribute to the emergence of new infectious diseases.
- Genetic recombination
- Evolution of new strains
- Antibiotic/pesticide use
- Changing weather patterns
- Modern transportation
- Ecological disaster/war/human expansion
- Animal control measures
- Public health failure
What is an example of a virus whose spread is affected by changing weather patterns? How?
Hantavirus is spread by deer mice, which are expanding their range because of climate change.
What is the definition of “epidemiology”?
The study of where and when diseases occur and how they are transmitted in populations.
What is the definition of “etiology”?
The cause, set of causes, or manner of causation of a disease.
What was epidemiologist John Snow known for doing in 1848-1849?
He mapped the occurrence of cholera in London.
What was epidemiologist Ignaz Semmelweis known for doing in 1846-1848?
Showed that handwashing decreased the incidence of pleural sepsis.
What was epidemiologist Florence Nightingale known for doing in 1858?
Showed that improved sanitation decreased the incidence of epidemic typhus.
What definition best describes “descriptive” epidemiology? Which known epidemiologist best embodies this approach?
The collection and analysis of data pertaining to a disease. John Snow.
What definition best describes “analytical” epidemiology? Which known epidemiologist best embodies this approach?
The analysis of a particular disease to determine its probable cause. Florence Nightingale.
What definition best describes “experimental” epidemiology? Which known epidemiologist best embodies this approach?
Involves a hypothesis and controlled experiments pertaining to a disease. Ignaz Semmelweis.
What organization publishes the “Morbidity and Mortality Weekly Report” (MMWR)?
The Centers for Disease Control and Prevention (CDC).
What is a notifiable infectious disease?
A disease which physicians are required to report if they see an occurrence.
What are some examples of well known notifiable diseases?
Any of:
AIDS, Chickenpox, Chlamydia, Cholera, Syphilis, Diptheria, Gonorrhea, Influenza, Hantavirus, Hepatitis A/B/C, HIV, Leprosy, Lyme disease, Malaria, Measles, Mumps, Plague, Rubella, etc.
When did Mycobacterium tuberculosis get put on the notifiable disease list? Is there a vaccine? How is it treated?
- There is a vaccine but it is unreliable. Treated with antibiotics (compliance very important).
What populations are at increased risk of contracting tuberculosis? Why?
First Nations and some African populations have a mutation in the NRAMP1 gene which increases susceptibility.
Who can initiate an outbreak investigation?
Clinicians, patients, Healthcare agencies with surveillance data, News agencies.
What 4 basic strain-typing techniques are used in molecular biology?
- PCR
- Hybridization
- Cloning
- Sequencing
What is “strain-typing” in epidemiology?
Molecular analysis of a disease to determine the strain.
What 3 main components are required for PCR?
- Primers
- Target DNA
- taq polymerase
What do each of Southern, Northern, and Western blotting techniques isolate?
Southern Blot: DNA
Northern Blot: RNA
Western Blot: Proteins
In what orientation are DNA sequences submitted for cataloguing?
Always 5’-3’.
When selecting a strain-typing method, why is it important to consider typeablility?
We want the test to generate an unambiguous result for whatever isolate we test.
When selecting a strain-typing method, why is it important to consider reproducibility?
We want the test to produce consistent identical responses for a given strain.
When selecting a strain-typing method, why is it important to consider stability?
We want to identify a character for molecular typing which is not subject to rapid evolution or lost by host.
When selecting a strain-typing method, why is it important to consider epidemiologic concordance?
Our method of molecular typing has to effectively group outbreak-related strains.
When selecting a strain-typing method, why is it important to consider typing system concordance?
Our method of molecular typing has to compare favourably with a previously validated test.
What 4 main methods are used for phenotypic strain typing?
Typing by:
- Growth and morphology
- Biochemical characteristics
- Function or physiology
- Serologic characteristics
What are some examples of techniques for phenotypic strain-typing using growth and morphologic characteristics?
- Gram staining
- Acid fast staining
- Growth on agar plates
What is an example of a technique used for phenotypic strain-typing using biochemical characteristics?
By targeting lactose fermentation we can detect Lactose-fermenting E. coli in the GI tract.
What are some examples of techniques for phenotypic strain-typing using functional or physiological characteristics?
- Toxigenicity bioassays
- Survival characteristics
- Multilocus enzyme electrophoresis
- Antimicrobial susceptibility
- Phage typing
- Cell culture assays
What is an example of a technique used for phenotypic strain-typing using biochemical characteristics?
Differentiation based on antigenic determinants. We identify inlfuenza strains based on H and N antigenic proteins.
What is a bacteriocin?
A short peptide that inhibits other bacteria.
What is ELISA? How can it be used for strain-typing?
Enzyme Linked Immuno-Sorbent Assay can identify antibodies to viruses that are present in the sample.
What 5 steps outline strain-typing by Western (Immuno-) Blot?
- Denature. Separate by electrophoresis
- Blot from gel to membrane
- Treat membrane w/ specific antibodies
- Add antigen-antibody complex markers
- Expose to film or substrate to reveal protein
What 3 main methods are used for genotypic strain-typing?
- Nucleic acid extraction
- Analysis of extrachromosomal DNA elements
- Genome-based typing methods
What are the 5 genome-based strain-typing methods mentioned in class?
- Restriction endonuclease analysis
- Southern Blot hybridization
- Pulse-Field Gel Electrophoresis (PFGE)
- Whole genome sequence comparison
- Microarray comparisons
During a restriction endonuclease analysis, what are some example of “rare cutters” which are required for genome analysis?
Not1, EcoR1, EcoR5.
Describe Pulse-Field Gel Electrophesis (PFGE). Why would we use this?
Like normal electrophoresis, but the angle of the electric field alternates by 120 degrees every 90 seconds for 18-24 hours. Used when the fragments would be too large for normal electrophoresis.
Do pathogenic bacteria tend towards smaller or larger genomes? Why?
Smaller genomes to streamline the replication process and increase pathogenicity.
What can PCR target?
A coding region (gene) or a non-coding region (repetitive element).
How can PCR be used to monitor CD4 and determine disease prognosis?
PCr can tell us whether the quantity of CD4 is keeping up with the infection (good) or beginning to drop off (bad).
What is spoligotyping?
Spacer oligonucleotide typing. A rapid PCR-based method for strain-typing
How would you calculate the incidence rate of a disease?
(# of people to develop a disease / total # of people all risk) * unit time
How would you calculate the prevalence of a disease?
(# of people with a disease / total # of people in group)
How would you calculate the mortality rate of a disease?
(# of people dead from a disease / total # of people in group) * unit time
