Clinical Epidemiology Flashcards
What is a basic science of public health that studies anything affecting population?
Epidemiology
What usually begins with outbreak of specific disease in community and identifies exposures that are associated with disease?
Study of epidemics in specific population groups
What do studies often provide?
The first indication of nature of new disease
Example: AIDS- Early 80s, many unusual cases of infection reported to CDC, epidemiologists examined shared risks and exposure in these patients to identify pathogen
Epidemiology involves the study of pattents of health and illness and associated factors at what level?
Population: Both infectious and non-communicable diseases
What are 3 reasons that epidemiology is one of the most important methods of public health research?
- It can identify risk factors for disease
- It can help determine optimal treatment approaches and prevention techniques
- Involves study design, data collection, statistical analysis, and documentation of results
Who is sometimes referred to as the father of epidemiology and why?
Hippocrates: He was the first person to examine relationships between disease and environmental influences and also coined the terms endemic and epidemic
Who identified the Broad Street pump as the cause of Soho cholera outbreak in 1854 and what was done do end the outbreak?
Dr. John Snow
-Used chlorine to clean water, then removed the pump handle
What was the 19th century cholera epidemic regarded as?
The founding event for epidemiology
What 2 types of disease does epidemiology follow?
Endemic and epidemic
Presence of disease in population at low but constant levels: Examples include common cold and heart disease?
Endemic
Sudden outbreak of disease in population, more cases than predicted within population: Examples include cholera epidemic in Haiti?
Epidemic
What is an epidemic that spreads throughout the world like AIDS or novel H1N1 Influenza?
Pandemic
What is a measure of new cases of disease or injury in population over specified time period?
Incidence
Ex: There were 34 cases of Lyme disease reported to Erie County Department of Health in 2010
-Incidence of LD in Erie County in 2010 = 34 cases
Measure of total number of cases of disease or injury in population over specified time period?
Prevalence
Ex: There are 40 students absent from class today due to influenza -Prevalence of influenza in class = 40 cases
What is prevalence at a specific point in time?
Point prevalence
Why is it important to identify the cause of disease outbreak?
Steps can be taken to treat or prevent disease in future
What can be used to identify probability of association between cause and disease outcome?
Biostatistics
True or False: Statistical association (or correlation) does not always equal causation
TRUE
-Ex: Studies have shown high correlation between number of violent crimes and ice cream consumption in a population
Cause and effect –> More likely explanation is that an area with more people is more likely to have a higher number of violent crimes committed and more ice cream consumption
What are the 9 Bradford-Hill Criteria for assessing evidence of causation?
- Strength
- Consistency
- Specificity
- Temporality
- Biological gradient
- Plausibility
- Coherence
- Experiment
- Analogy
Larger association is more likely causal effect?
Strength
Stronger association when same findings observed by different people and different samples?
Consistency
Causation likely is very specific population with specific disease and no other likely explanation
-More specificity = Bigger probability of causal effect
Specificity
Temporality?
Effect happens after the cause (CA happens after exposure to radiation)
Biological gradient?
Greater exposure causes greater incidence
Plausible mechanism between cause and effect helpful?
Plausibility
Between epidemiological and laboratory findings increases likelihood of effect?
Coherence
“Occasionally it is possible to appeal to experimental evidence?
Experiment
Analogy?
The effect of similar factors may be considered
What is a qualitative study?
Case study (case series studies)
What is a quantitative study?
Case-control studies and cohort studies
What is a qualitative study of one patient or a small group of patients with similar disease?
Case Series Studies
True or False: Case series studies are only descriptive and cannot be extrapolated to a population of patients with disease
TRUE
What compares patient exposure periods to periods when they are unexposed?
Self-controlled case-series studies
What 2 things are done in a self-controlled case-series study?
- Patients are diagnosed with the disease and followed
2. Follow-up time is divided into exposed and unexposed periods and incidence of disease compared
What is a retrospective study that looks in patient’s past for possible exposures that may have been encountered?
Case-control studies
In a case-control study, who are “cases”?
Patients diagnosed with disease
In a case-control study, who care “controls”?
Patients not diagnosed with disease
What other factors should be matched as closely as possible between cases and controls in a case-control study?
Age, sex, ethnicity, etc.
In a case-control study, once the exposure is identified, what 4 categories are cases and controls subdivided into?
- Exposed cases
- Exposed controls
- Unexposed cases
- Unexposed controls
What is the formula fr the odds ratio used in a case control study?
OR = (Exposed cases/Unexposed cases) / (Exposed controls/Unexposed controls)
If the odds ratio is greater than 1, what does this mean?
The exposure is likely associated with disease
If the odds ratio is equal to 1 or is close to 1, what does this mean?
Exposure and disease are not likely associated
What is a prospective study that selects participants based on exposure status?
Cohort study
In a cohort study do participants have the disease at the initiation of the study?
No, participants are at risk of, but don’t have the disease at the initiation of the study
So, what is actually done when in a cohort study?
The cohort is followed prospectively for development of disease
Example: Cohort of smokers and cohort of non-smokers followed over time to estimate incidence of lung cancer
In a cohort study, the cohort if followed prospectively for outcome, what are the 4 categories used?
- Cases in exposed group
- Non-cases in exposed group
- Cases in unexposed group
- Non-cases in unexposed group
What is the formula for relative risk used in a cohort study?
RR = (Cases in exposed group/Cases in exposed group + Non-cases in exposed group) / (Cases in unexposed group/cases in unexposed group + non-cases in unexposed group)
What does it mean if RR is greater than 1?
Exposure is likely associated with development of disease
What does it mean is RR is equal to 1 or close to 1?
Exposure and disease aren’t likely associated
True or False: OR is a more powerful measure than RR?
FALSE… RR is more powerful measure than OR
Is true incidence calculated in a case control study?
NO
To investigate an outbreak, what 2 things are essential?
Speed and Validity
What are the 10 steps epidemiologists use to systematically investigate outbreak?
- Prepare for fieldwork
- Establish existence of outbreak
- Verify diagnosis
- Define and identify cases
- Describe data in terms of time, place, person
- Develop hypotheses
- Evaluate hypotheses
- Refine hypotheses, carry out additional studies
- Implement control and prevention measures
- Communicate findings
What 2 things are done to prepare for field work?
- Research disease, gather supplies and equipment
2. Consult all parties to determine your role (who are local contacts)
What must be done to establish the existence of outbreak?
Verify that the suspected outbreak is a real outbreak
- True outbreaks with common cause
- Unrelated cases of same disease
- Unrelated cases of similar but unrelated diseases
What is seen if an outbreak exists?
The observed number of cases is greater than the expected number of cases
How do you determine the expected number of cases?
Find historical data for previous cases through the health department, hospital discharge, and mortality records
In what situations might would the observed number of cases being greater than the expected number not indicate outbreak?
Changes in population, new diagnostic techniques
What must be done to verify the diagnosis?
- Review clinical findings and lab results (make sure the diagnosis is accurate and the lab tests are correct)
- Visit with patients to get a detailed history for shared risk factors
What questions should be asked when visiting the patients and getting a detailed history?
- What were exposures before becoming ill?
- What do they think caused their illness?
- Do they know anyone else with the disease?
- Do they have anything in common with others who have the disease?
What should be done if you are uncertain about lab tests?
Have a specialists review and order secondary tests
What is done to define and identify cases?
Establish case definition (classify patients as having the disease or not)
What are the 4 components usually used in case definition?
- Clinical information (Presence of fever (> 101oF), 3 or more loose stools/d)
- Characteristics about pts affected (Swam in same lake)
- Information about location or place (Wedding banquet, certain restaurant) –> Restricts definition
- Time during which outbreak occurred (New cases in past month)
What is a confirmed case defined by?
Having lab verification
Ex. Isolating EHEC from stool culture or presence of HUS
What is this an example of?
- School-aged child
- Resident of county
- Had GI symptoms between November 3-8, 1990
Restrictions
What is a probable case defined by?
Typical symptoms with no lab confirmation
Ex. Bloody diarrhea (but no culture) and same restrictions
What is a possible case defined by?
Few typical symptoms
Ex. Abdominal cramps and diarrhea (at least 3 stools in a 24-hour period) and same restrictions
What are 2 ways to identify and count cases?
- Passive surveillance
2. Active surveillance
What is an example of passive surveillance?
Sending out a letter describing situation
What is an example of active surveillance?
Telephone or visit facilities to collect information
Who sometimes alerts the public about an outbreak?
Public health officials
-Can tell public to avoid contaminated food product or consult physician if symptoms are present
When defining and identifying cases, what should be collected regardless of disease?
- Identifying information: Name address, phone number, email
- Demographic information: Age, sex, race, occupation
- Clinical information: Symptoms and date of onset
- Risk factor information: Exposure to food, water sources
How should data be collected on questionnaire?
Line listing with all data fields collected for each patient
In terms of describing data in terms of time, place, and person, what 2 things will descriptive epidemiology do?
- Show what information is reliable and informative (If same unusual exposure is reported by many patients and what may not be as reliable like many missing or “don’t know” responses)
- Provides comprehensive description of outbreak (shows trend over time, geographic extent, populations affected)
Characterizing an outbreak by time is important as well, what is an epi curve?
Shows the number of cases by date of onset
Example with Legionnaires’ disease in Philadelphia in 1976
What can tell where you are in the course of an epidemic and project its future course?
Epi curve
What can an Epi curve tell you about exposure?
It can estimate the probable time period
What does the shape of an Epi curve determine?
Pattern of epidemic, exposure time, incuation
What type of epidemic has an Epi curve with a steep up slope and gradual down slope?
Single source epidemic: People are exposed to the same source over a brief period
What i seen with a continuous common source epidemic?
It has a plateau instead of peak
What is seen with a person-to-person spread?
A series of progressively taller peaks 1 incubation apart
What can show where affected people live, work, and may have been exposed and what does this provide information on?
- Spot Map
- Geographic extent
What might been seen on a spot map?
Clusters or patterns: Proximity to water, restaurant, or grocery store
What does hospital clustering usually indicate?
Focal source or person-to-person spread
What is more consistent with a common source like a dining hall?
Scattering of cases throughout a facility
When can a sport map be misleading?
If the size of population varies between areas affected
What should be used if the size of a population varies between areas affected?
The proportion of patients in each area (attack rate)
What are 2 categories used to determine populations at risk?
- Personal characteristics: Age, race, sex, medical status
2. Exposures: Occupation, leisure activities, use of medications, tobacco, drugs
What should address the source of the agent, mode of transmission, and possible exposures?
Hypotheses
What are 4 questions that should be asked when developing hypotheses?
- What is the agent’s usual reservoir?
- How is it usually transmitted?
- What vehicles are commonly implicated?
- What are known risk factors?
What can help provide some hypotheses?
Descriptive epidemiology
What can an Epi curve show to help provide some hypotheses?
- Narrow period of exposure
- Geographic distribution
- Groups with particular age, sex, other characteristics
What 2 things can be done to evaluate hypotheses?
- Compare hypothesis with established facts
2. Use analytic epidemiology
When can you just compare hypotheses with established facts?
If there is strong evidence
-Vitamin D intoxication linked to more vitamin D being added to milk than recommended
When do you need to use analytic epidemiology to test hypotheses?
When the cause is unclear
What are 2 types of analytic epidemiology used to test hypotheses?
- Cohort study
2. Case-control study
What compares patients exposed to risk factor with unexposed patients?
A cohort study
What compares patients with disease to patients without disease?
A case-control study
What is best for a small, well-defined outbreak (like gastroenteritis in people who attended a wedding where a complete list of wedding guests was available)?
A cohort study
In the gastroenteritis example, what 2 questions should be asked on the questionnaire to assess exposure and disease?
- What food/drink he or she had consumed at the wedding
2. If he or she had become ill with gastroenteritis
What should be calculated in a cohort study?
Attack rates for
- People who ate particular item (were exposed)
- People who didn’t eat that item (weren’t exposed)
What is the equation for exposed group attack rate?
Sick patients who ate item/Total # of people who ate item
What is the equation for unexposed group attack rate?
Sick patients who didn’t eat item/Total # of people who didn’t eat item
When identifying the source of an outbreak, you want to look for the item with what 3 things (using a cohort study)?
- High attack rate among those exposed
- Low attack rate among those not exposed
- -> Ratio between attack rates for 2 groups is high - In addition, most people who became ill should have consumed item: Exposure could explain most, if not all cases
Once the source of the outbreak is identified, what should be done?
Calculate the relative risk for the item
What is best for an outbreak in a large population?
A case-control study
In a case-control study who is asked about exposures?
Both patients (“cases”) and conrols
True or False: Case control studies prove exposure caused disease
FALSE: Case-control studies do not prove exposure caused disease, but can help evaluate possible sources
In a case-control study, you don’t know the number of people in a community who were and were not exposed, so what does this mean for the relative risk?
You can’t calculate it
In a case-control study, what do you calculate and how is it arranged?
The odds ratio, arranged in a 2x2 table
When do you do additional epidemiological studies?
When the analytic epidemiological studies don’t confirm the hypothesis –> You reconsider the hypothesis and look for new sources
Even is an association is identified, what might still be needed?
More specific exposure histories
In a study of a community outbreak of botulism in IL, what were the 3 case-control studies used to identify the source?
- Exposures of cases/controls from public: This implicated a restaurant
- Compared menu items eaten by cases/ controls: This identified specific menu item, meat and cheese sandwich
- Radio broadcast to identify health persons who had eaten a sandwich: This found that controls were less likely than cases to have eaten onions that came with sandwich
-Type A C. Botulinum was identified from a pan of leftover sauteed onions
What other 2 things are important in refining hypotheses and carrying out additional studies?
- Laboratory and environmental studies (need lab tests to isolate bug or confirm source)
- Environmental studies help explain why outbreak occurred (linking sewage plant to shigellosis outbreak)
When should implementing control and prevention measures be done?
ASAP
What should implementing control and prevention measures be aimed at?
Specific links in chain of infection, agent, source, or reservoir
What can be done to implement control and prevention measures? (3)
- Destroy contaminated foods, sterilize contaminated water
- Destroy mosquito breeding sites
- Make infected food handler to stay away from work until well
What should control measures be aimed at?
Transmission or exposure
What are some examples of control measures? (3)
- Limit airborne spread of agent in nursing home residents: Put infected people in separate area to prevent exposure to others
- Wear insect repellent, protective clothing in areas of LD risk
- Malaria chemoprophylaxis for travelers
What are the 2 forms of communication for outbreaks?
- Oral briefing for local health authorities
2. Written report
Who is an oral briefing for and what can you do during it?
- For local health authorities and people responsible for control and prevention
- You can defend you conclusions and recommendations if necessary
What format is a written report in?
Scientific
What 4 things does a written report do?
- Provides blueprint for action
- Serves as record of performance,
- Document for potential legal issues
- Reference for future, similar situations
