Epidemiology (midterm) Flashcards

Question

How are hypotheses of the determinants of health-related events proven or disproven?

Answer 1

Through analytical studies (case–control and cohort studies), experimental studies, and the use of statistical hypothesis testing throughout

Answer 2

Developing scientifically sound health programs, interventions, and policies

Answer 3

Not only the health of patients as individuals, but anything in the environment that may affect their health and well-being in any way

Answer 4

That the unit of study is a population, not individuals

Answer 5

* Endemic: the habitual presence or usual prevalence of a given disease in an area * Epidemic: the occurrence of a group of illnesses in an area, clearly in excess of normal expectancy (outbreak) * Pandemic: a worldwide epidemic

Answer 6

* Registration of births, deaths, and diseases * Population censuses * Routine health information systems * Surveillance * Investigation of epidemics * Sample surveys

Answer 7

* Supernatural theories: a curse, the evil force of a demon * Hippocratic theory * Miasmatic theory * Theory of contagion * Germ theory (Henle–Koch postulates) * Classic epidemiologic theory (agent–host–environment theory) * Multicausality and webs of causation

Answer 8

1. Agent of disease 2. Susceptible host 3. External environment

Answer 9

* Infectivity: proportion of **exposed** persons who become **infected** (i.e. when the agent multiplies in the host) * Pathogenicity: proportion of **infected** persons who develop **clinically apparent disease** * Virulence: proportion of **clinically apparent cases** that are **severe or fatal**

Answer 10

* Infectivity * Pathogenicity * Virulence

Answer 11

An infectious microorganism or pathogen, **as well as** chemical and physical causes (e.g. poisons, smoke, repetitive mechanical stress in carpal tunnel)

Answer 12

The human who **can get** the disease/health-related event

Answer 13

* Exposure, i.e. practices, personal choices * Susceptibility, e.g. genetic composition, psychological status, age, sex * Response to the causative agent

Answer 14

The extrinsic factors that affect the agent, host, and opportunity for exposure

Answer 15

* Physical factors, e.g. geology, climate * Biological factors, e.g. insect vectors * Socioeconomic factors, e.g. crowding, sanitation, availability of health services

Answer 16

The sum of all factors that contribute to the occurrence of a disease (agent factors + host factors + environmental factors)

Answer 17

Multicausal theory/web of causation

Answer 18

* Direct: A causes B without intermediates (very rare) * Indirect: A causes B with intermediates (i.e. by the effect of C, D, etc.)

Answer 19

* Sufficient factors: the occurrence of these factors inevitably produces disease, but these factors may not be present in every occurrence * Necessary factors: disease cannot occur without these factor, but these factors alone may not be enough to cause the disease

Answer 20

Neccessary, **but not** sufficient ## Footnote E.g. AIDS will never occur in the absence of exposure to HIV, but not every person exposed to HIV will develop AIDS

Answer 21

Sufficient, **but not** necessary ## Footnote Each of the factors in the question is enough to cause lung cancer on its own, but not every case of lung cancer will include exposure to any of the three

Answer 22

**Neither** sufficient **nor** necessary

Answer 23

* Public health action does not depend on the identification of every cause, as no single cause is enough to cause the disease, nor will a single cause be found in all cases * These diseases may be preventable by blocking a single factor out of the many factors

Answer 24

The progression of a disease process in an individual over time in the absence of treatment ## Footnote E.g. the natural history of HIV/AIDS includes some clinical presentation within the first few months (acute retroviral disease) but then latency for around 10 years until AIDS-proper develops, and usually terminates with death

Answer 25

Chronic carriers remain infectious after recovery from the clinical illness, or may have never exhibited symptoms

Answer 26

* Hepatitis B * Typhoid fever

Answer 27

Unapparent

Answer 28

Moderate clinical severity

Answer 29

The habitat in which the agent normally lives, grows, and multiplies, be it humans, animals, or the environment. This may or may not be the source of infection. ## Footnote E.g. for *Clostridium botulinum* (the bacterium causing botulism), the source of infection is usually improperly canned food containing spores, **but the reservoir is soil**

Answer 30

The naturally occuring disease may be eradicated, as with smallpox in 1977

Answer 31

* Brucellosis (from cows and pigs) * Anthrax (from sheep) * Plague (from rodents) * Trichinellosis/trichinosis (from pigs) * Rabies (from bats, raccoons, dogs)

Answer 32

* HIV/AIDS * Ebola * SARS and COVID-19

Answer 33

The path by which a pathogen leaves its host, usually corresponding to where the pathogen is localized in the host ## Footnote E.g. respiratory infections like *Mycobacterium tuberculosis* exit via the respiratory tract. Other agents exit by the blood, whether through direct exposure (e.g. HIV, hepatitis B) or by a vector (e.g. malaria)

Answer 34

* Skin-to-skin contact * Kissing/saliva * Sexual contact * Droplets produced by sneezing, coughing, talking, etc.

Answer 35

* Airborne: via dust or aerosols (droplet nuclei) * Vehicleborne: via food (e.g. botulism), water (e.g. cholera), biologic products like blood, or fomites * Vectorborne (using another organism): the organism may carry the infectious agent by purely mechanical means (e.g. fleas, lice, ticks) or may support biological changes in the agent (e.g. mosquitoes in malaria)

Answer 36

The manner through which the pathogen enters a susceptible host and gains access to tissues in which it can multiply or act

Answer 37

* Respiratory tract (e.g. cholera) * GI tract and the fecal–oral route * Skin (e.g. hookworm) * Mucous membranes like the vagina (e.g. syphilis) * Blood (e.g. hepatitis B)

Answer 38

Developing specific immunity in a certain percentage of the population (whether from prior infection or immunization) to limit the number of susceptible hosts that the agent can infect

Answer 39

* The disease must be restricted to a single host species (e.g. smallpox in humans) * There must be relatively direct transmission * Infections/immunization must produce solid, specific immunity

Answer 40

RR = risk in exposed/risk in not exposed i.e. RR = [a/(a+b)]/[c/(c+d)]

Answer 41

* Chi-squared (χ²) test * Relative risk/risk ratio * Odds ratio * Attributable risk

Answer 42

≥ 3: high association 1.5–2.9: moderate association 1.2–1.49: weak association 1: no association < 1: negative association (protective effect)

Answer 43

RR measures the risk of the outcome in those exposed compared to those not exposed. A RR of 5 means those exposed are 5 times more likely to develop the outcome compared to those not exposed.

Answer 44

Cohort studies

Answer 45

Whether there is an association between two **categorical** variables, and the probability that this association is purely due to chance (P value)

Answer 46

If the P-value ≤ α-value (where α is usually 0.05), there is a significant association i.e. if the test statistic is greater than the critical value

Answer 47

It only tells us if there is an association, not how strong this association is

Answer 48

Cross-sectional studies

Answer 49

OR = (a∙d)/(b∙c)

Answer 50

OR measures the probability that those with the disease were exposed, compared to those who do not have the disease An OR of 5 means that those with the disease are 5 times more likely to have been exposed compared to those without the disease

Answer 51

Case–control studies

Answer 52

1. The selected controls are representative of the general population 2. The selected cases are representative of all cases 3. The disease is rare

Answer 53

AR = a/(a+b) – c/(c+d) AR% = [a/(a+b) – c/(c+d)] ∙ 100/[a/(a+b)] ∴ AR% = (AR ∙ 100)/[a/(a+b)]

Answer 54

﹥0: positive association = 0: no association < 0: negative association (protective effect)

Answer 55

AR measures the risk of the outcome in the exposed due to exposure alone, not due to other factors An AR of 3 means those exposed are 3 times more likely to develop the outcome due to this exposure alone, removing the risk due to other factors E.g. for smoking and lung cancer, those who smoke are 3 times more likely to develop lung cancer due to the fact that they smoke alone

Answer 56

AR% measures how much of the outcome among those exposed is directly attributable to the exposure, not other factors An AR% of 90% means that 90% of the outcome among exposed is due to the exposure alone E.g. for smoking and lung cancer, 90% of the lung cancer cases are due to the individuals smoking, not due to other factors

Answer 57

The AR values suggest the amount of the disease that could be eliminated if the exposure is controlled or eliminated. E.g. for smoking and lung cancer, an AR of 90% means that 90% of cases of lung cancer among smokers could have been prevented if they did not smoke. The remaining 10% are due to other factors and may still have occurred if the individuals did not smoke

Answer 58

No, e.g. age

Answer 59

The concurrence of two variables more often than would be expected by chance

Answer 60

* Spurious (false) associations * Indirect (confounding) association * Direct (causal) associations: one-to-one or multifactorial

Answer 61

1. Evaluate the results of the study and ensure that they are accurate: evaluate the method, validity, reliability, and bias 2. Perform statistical analysis on the results (calculate P-value, confidence interval). If the P-value is not significant, this may be due to a small sample size (**low power**) 3. If the P-value is significant, evaluate whether the relationship is indirect—the presence of a **confounder** 4. If the possibility of confounding is excluded, apply the criteria of causation

Answer 62

Systematic—once it is introduced to the study, it cannot be corrected

Answer 63

**Selection bias**: distortion in the selection of participants, either: * A difference in those selected to participate and those who were not, or * A difference in those selected for the treatment group and those selected for the control group **Information bias**: distortion in the way the data were obtained from the study groups (e.g. recall bias)

Answer 64

Those in the "outcome" group are more likely to remember possible exposure than those in the "non-outcome" group

Answer 65

1. Must be a risk factor for the disease independently 2. Must be associated with the exposure under study 3. Must not lie on the causal pathway between the exposure and the disease

Answer 66

* At the design stage: restriction, matching, randomization * At the analysis stage: stratification, multivariate analysis, standardization

Answer 67

**Most important criteria** * Temporality: cause precedes effect * Strength of association: large RR or AR * Consistency: the exposure–outcome repeatedly observed by different people in different places under different circumstances at different times **Other criteria** * Biological gradient (dose–response): increasing the exposure is associated with higher rates of disease, and vice versa * Biological plausability: causation makes sense according to biological knowledge of the time * Experimental evidence **Additional, non-necessary criteria** * Analogy: similar cause–effect relationships established for related diseases * Specificity: one cause leads to one effect * Coherence: relationship doesn't seriously conflict with known facts of the disease and its biology

Answer 68

A systematic investigation to develop or contribute to generalizable knowledge

Answer 69

A specific plan or protocol for conducting the study, which allows the investigator to translate the conceptual hypothesis into an operational one

Answer 70

* Descriptive: cross-sectional, case report, case series, ecological studies, surveys * Analytical: case–control, cohort studies

Answer 71

* Community trial (community assignment) * Clinical trial (individual assignment)

Answer 72

One that watches for outcomes based on specific exposure, e.g. cohort studies

Answer 73

One that looks backwards to examine exposures based on an identified outcome

Answer 74

Case report

Answer 75

Case–control study

Answer 76

* Cannot estimate prevalence or incidence (except if the outcome is surveilled, e.g. breast cancer) * There is no control group for comparison

Answer 77

Drawing unfounded conclusions about exposure–outcome association **on the individual level** from data on the population level ## Footnote E.g. in Country A, 72% of people eat 5+ pieces of fruit a day, compared to 24% in Country B. In Country A, the rate of obesity is 34%, compared to 66% in Country B. We **cannot** say that eating 5+ pieces of fruit a day decreases your chances of being obese, as those in Country A who eat 5+ pieces of fruit a day may not be those with the low BMIs

Answer 78

Populations/aggregates of individuals

Answer 79

Looking for associations and correlations (correlation requires that both variables are continuous) * Pearson's product–moment correlation coefficient (*r*) * Spearman's rank correlation coefficient (ρ)

Answer 80

* Disease prevalence * Prevalence rate ratio (PRR) = [a/(a+b)]/[c/(c+d)] {similar to risk ratio but for prevalence, not incidence}

Answer 81

No, as temporality cannot be determined

Answer 82

* Rare diseases * Diseases with a long latency period

Answer 83

Similar to the case group in all respects except having the disease

Answer 84

Odds ratio (OR)

Answer 85

* Recall bias * Confounding variables

Answer 86

Case–control studies

Answer 87

Cohort studies

Answer 88

* Incidence * Relative risk/risk ratio (RR)

Answer 89

* Prospective cohort * Retrospective cohort * Ambidirectional cohort

Answer 90

The best standard of care. Giving an inert placebo in this case is considered unethical

Answer 91

1. Background information and expert opinions 2. Case reports and case series 3. Case–control studies 4. Cohort series 5. Randomized controlled trials 6. Critically appraised topics 7. Systematic reviews 8. Meta-analyses

Answer 92

* Case reports/case series * Case–control studies * Cohort studies * Randomized controlled trials

Answer 93

* Criticaly appraised topics * Systematic reviews * Meta-analyses

Answer 94

A short summary of the evidence on a topic of interest, usually focused on a clinical question

Answer 95

Critically appraised topic

Answer 96

They have a short useful lifetime if they are not updated with new information

Answer 97

A literature review that considers the entirety of available literature to provide a comprehensive overview of a subject and minimize bias

Answer 98

In research databases like Cochrane or PubMed

Answer 99

A systematic review that summarizes information from all studies on a specific clinical question, using **quantitative, statistical methods** to determine whether findings are reliable and applicable to different populations

Answer 100

* Unfiltered information: shaped by the researcher's approach—the researcher is the primary source of data collection * Filtered information: the researcher applies quantitative or qualitative methods to filter information from unfiltered sources

Answer 101

A meta-search engine and database for searching through **both filtered and unfiltered** medical research (similar to Google Scholar)

Answer 102

The lower part of the pyramid—they are less reliable due to lack of rigorous peer review and a systematic methodology

Answer 103

The systematic ongoing collection, collation, analysis, and interpretation of health data; the evaluation of public health practice; and the timely dissemination of these data to those who need to know | (Combined WHO and US CDC definitions)

Answer 104

* Following trends in the health status of a population over time * Establishing health care and public health priorities * Ensuring those with the greatest need are prioritized * Detecting and responding to epidemics * Evaluating the effectiveness of programs and services

Answer 105

* Giving early warning of changes in incidence (e.g. the recent increases in tuberculosis cases in many countries) * Early detection of outbreaks * Evaluating the effectiveness of interventions (e.g. a new vaccine)

Answer 106

* Epidemic diseases (e.g. measles, meningococcal meningitis) * Malnutrition * Animal reservoirs and vectors of communicable diseases * Environmental pollution, especially water pollution * Demographic events, e.g. births and deaths

Answer 107

* There must be a baseline figure on deaths due to malaria * There must be a way of monitoring the trends in deaths due to malaria over time

Answer 108

* Passive surveillance * Active surveillance * Negative surveillance * Sentinel surveillance * Mortality surveillance

Answer 109

* Data are generated without intervention or contact by the surveilling agency * Other agencies will initiate reporting * E.g. for notifiable diseases, like anthrax, cancers, COVID-19

Answer 110

* The surveilling agency initiates procedures to obtain reports * The data collator ensures that the reporting agency is in fact collecting data to the fullest degree

Answer 111

* The surveilling agency requires the collector to report **even the absence** of cases * Ensures that a "nil report" truly reflects zero incidence, not a failure to report * E.g. for uncommon disorders, pediatric conditions

Answer 112

* The surveilling agency selects (either randomly or intentionally) a small group of health workers from whom to gather data * Often produces more detailed data on cases of illness because the participating health workers may receive incentives * E.g. analyzing the nasopharyngeal swabs from **all patients** at **only 15** COVID-19 swabbing sites to analyze and identify the strain of the virus

Answer 113

* Present in most countries—the requirement that every death in the population be reported or registered * Yields a death rate * Countries differ in the quality and completeness of their death registers

Answer 114

Death is the common final outcome of severe diseases. Changes in death rates can be an indicator of changing health status of a population

Answer 115

* Problem * Data gathering * Data analysis/integration * Intervention (loops back to step 1)

Answer 116

1. Data collection 2. Data collation 3. Data analysis 4. Dissemination (often with resulting action)

Answer 117

* Primary: preventing disease when risk factors are present (e.g. by immunization, lifestyle modification) * Secondary: preventing complications when the disease is present (e.g. by early diagnosis, sustained care) * Tertiary: prevention of disability or death (e.g. by rehabilitation) * Quaternary: prevention of over-diagnosis and over-treatment from interventions which are too invasive or ethically unacceptable (using evidence-based medicine)

Answer 118

The **systematic** application of a test or inquiry to identify individuals at **sufficient risk** of a specific disorder to benefit from further investigation or direct prevention among persons **who have not sough medical attention from symptoms of that disorder** | (Wald, 2004)

Answer 119

* Better prognosis for individuals * Protecting the public from communicable diseases * Rational allocation of resources * Research into the natural history of disease

Answer 120

Screening someone when they come into contact with the health system **for another reason** E.g. * Checking the lipid profile for an overweight or obese patient when they come to your clinic (screening for diabetes) * Referring all women at your clinic within a certain age range for cervical or breast cancer screening

Answer 121

Early detection/diagnosis is based on symptoms and signs, while screening is performed for people who are usually asymptomatic

Answer 122

* The disease is an important, well-defined health problem with known epidemiology, well-understood natural history, and prevalent undiagnosed cases * The presence of a presymptomatic or early stage, where screening would be actually beneficial

Answer 123

* Safe * Inexpensive * Acceptable * Reliable * Valid * No, or minimal, adverse effects (e.g. pain, radiation exposure)

Answer 124

* Sensitivity * Specificity * False positive rate * Positive predictive value (PPV) * Negative predictive value (NPV)

Answer 125

The ability of a screening test to correctly identify those **with** the disease = TP/(TP + FN)

Answer 126

The ability of a screening test to correctly identify those **without** the disease = TN/(TN + FP)

Answer 127

The proportion of "positive" results that are erroneous—incorrect identification of disease = FP/(FP + TN) = 1 – specificity

Answer 128

Estimates the magnitude of: * the economic effects of a false positive (further testing, investing health care resources) * the psychological distress of a false positive

Answer 129

The likelihood that someone with a "positive" result actually has the disease = TP/(TP+FP)

Answer 130

The likelihood that someone with a "negative" result actually does not have the disease = TN/(TN+FN)

Answer 131

= (TP + FN)/(N), where N is the total sample size

Answer 132

* Evaluating the economics of the program * Setting the cut-off age based on local data * Improving performance from the experience gained * Comprehensive assessment of the screening process * Quality assessment of staff * Assessing the barriers to screening

Answer 133

A perceived longer survival time in those who underwent screening as they were detected at a stage too early for effective treatment E.g. a person who underwent early brain cancer screening survived 8 years, compared to 3 years for a person diagnosed from symptoms. If the person who underwent screening were left to be diagnosed from symptoms, they may too have survived for only 3 years—there is a 5 year lead time bias.

Answer 134

Screening tends to detect cases where the disease is progressing slowly due to a longer asymptomatic phase, inflating the survival rate Those with severe, short disease have a very short asymptomatic phase, and so wouldn't be detected from screening anyway

Answer 135

Those who volunteer for screening tend to be: * of a higher socioeconomic class, * more health-conscious, and * comply with prescribed advice better. Therefore the percieved benefits of screening may only be the benefits of volunteerism