Epidemiology Midterm / S00

For multiple-choice questions, provide the single best response. For open-ended questions, please be brief and concise. For problems involving calculations, show all work. Point values are indicated in [square brackets]. The time limit for this test is 60 minutes.

Chapter 1

(1) Epidemiology and Public Health are both concerned with the prevention of disease and the promotion of health in populations. How do they differ? [3]

ANS: Epidemiology is mostly a ["study of"]. Public health is largely an ["activity or organized effort"]

(2) List the three most common causes of death in the United States, as of 1992, in their correct order: [3]

(A) ____________________________
(B) ____________________________
(C) ____________________________

ANS: (A) Heart disease (B) Cancer (C) Injuries / External Cause

(3) How do the above three diseases differ from the primary causes of death that occurred at the turn of the last century? [2]

ANS: The most common causes of death today are [chronic] and [non-contagious]. Most of the common causes of death at the turn of the prior century were [acute] and [contagious] (the exception being TB, which is chronic and contagious).

(4) Define "epidemic." [2]

ANS: An epidemic is a clear excess above normalcy of disease or disease-related condition in a definable population.

(5) Define "endemic." [2]

ANS: Endemic means that the disease is occurring at is usual or expected rate.

(6) Define "morbidity." [2]

ANS: Morbidity mean related to disease or disability.

(7) Name the physician who removed the handle from the Broad Street pump. [1]

ANS: John Snow

Chapter 2

(8) List a synonym for "incubation period." [1]

ANS: Any of the following: latent period, induction period, or preclinical stage of disease

(9) Match the definitions below with one of the following terms: (A) contributing cause; (B) natural history of disease; (C) necessary cause; (D) primary prevention; (E) secondary prevention; (F) stage of clinical disease; (G) stage of susceptibility; (H) stage of subclinical disease; (I) sufficient cause (J) tertiary prevention
Definition Term
A causal factor that is neither necessary nor sufficient, but increases the likelihood of disease, all other things being equal. (A) contributing cause
Any factor that must be present for the disease to occur. (C) necessary cause
Any factor or, more commonly a constellation of factors, that inevitably lead to the disease (I) sufficient cause
Preventive measures that occur during the stage of subclinical disease, intended to delay the onset of disease or reduce its duration or severity (E) secondary prevention
Preventive measures aimed at the stage of susceptibility, intended to reduce new occurrences of disease. (D) primary prevention
Preventive measures that are intended to reduce the complications and disabilities associated with an ongoing disease. (J) tertiary prevention
The stage of disease the follows exposure to the agent but is before symptoms are apparent. (H) stage of subclinical disease
The stage in the natural history of a disease that precedes exposure to the causal agent. (G) stage of susceptibility
The progression of a disease in an individual over time. (B) natural history of disease
The stage of disease associated with signs and symptoms (F) stage of clinical disease

(10) Distinguish between a "risk indicator" and "risk factor." [2]

ANS: A risk indicator is a factor that is statistically associated with a disease but is not necessary causal. A risk factor is truly causal.

Chapter 3

(11) The habitat or environment in which an infectious agent lives and multiplies is called its ________________________.

ANS: reservoir

(12) All infectious diseases are associated with infections but not all infections are associated with disease. Please explain. [2]

ANS: Infections can be asymptomatic.

(13) List four of the five elements of the infectious disease process [5]

(A) ______________________________________
(B) ______________________________________
(C) ______________________________________
(D) ______________________________________

ANS: (A) agent (B) reservoir (C) portals (D) transmission (E) host immunity

(14) List two examples of portals. [2]

(A) ______________________________________
(B) ______________________________________

ANS: Any two of the following: respiratory tract, conjunctiva, urogenital tract, gastrointestinal tract, placenta.

(15) Provide an example of a physical barrier to infection. [1]

ANS: Any of following: skin, mucosal linings, mucus sheaths, respiratory tract cilia, cough and gag reflex

(16) Provide an example of a chemical barrier to infection. [1]

ANS: Any of the following: acidity of stomach and vagina, enzymes in saliva and GI tract, lipids, interferons, and other miscellaneous biologically active substances.

(17) How does a modified live vaccine differ from a killed vaccine? [2]

ANS: Modified live vaccines are composed of non-virulent strains of the agent, modified to be nonpathogenic. "Killed" vaccines are agent proteins that are incapable of replicating themselves.

Chapter 4

(18) Match the definitions below with the following terms

- sign
- symptom
- test.

___________ The subjective perceptions of disease made on the part of the patient.
___________ A measures of physiologic or immunologic function.
___________ An observation indicative of a disease made by an examiner.

(19) Define reproducibility. [2]

ANS: [repeatability / consistency]

(20) A kappa statistic of 1 indicates (select best response):

(A) Perfect agreement
(B) Good agreement
(C) Poor agreement
(D) Random agreement

ANS: (A)

(21) This problem is similar to the problems in the case study in which we backfilled a sensitivity / specificity table in order to determine the predictive value positive of a test in a population. Suppose, we start with a population of 10,000 individuals in which the prevalence of disease is 5% (0.05). A test that is 96% sensitive (SEN = 0.96) and 98% specificity (SPEC = 0.98) is used to uncover latent infection in the population. Based on this information, fill in all boxes with "______", below. (Use the blank back of the prior page to show your work.)

D+ D-
T+ 480_____ 190_____ 670_____
T- 20_____ 9310_____ 9,330_____
500_____ 9,500_____ 10,000

ANS:

m1 = (N)(P) = 500

m2 = N - m1 = 10,000 - 500 = 9,500

TP = (SEN)(m1) = (.96)(500) = 480

FN = m1 - TP = 500 - 480 = 20

TN = (SPEC)(m2) = (.98)(9500) = 9,310

FP = m2 - TN = 9500 - 9310 = 190

n1 = TP + FP = 480 + 190 = 670

n2 = FN + TN = 20 + 9310 = 9330

(22) The predictive value positive of the above test in the above population is = __________

ANS: PVP = (TP) / n1 = 480 / 670 = 0.7164

(23) The predictive value negative of the above test in the above population = __________

ANS: PVN = (TN) / n2 = 9310 / 9330 = 0.9979

(24) Do you think it would be safe to tell someone who tests positive in the above population that they are indeed infected? Justify your response. [2]

ANS: [No,] [since they have only ~72% of actually being a true positive, i.e., PVP = .716].

(25) Do you think it would be safe to tell someone who tests negative in the above population that they are free from infection? Justify. [2]

ANS: [Yes,] since there is an almost 99.8% chance of being correct, i.e., [PVP = .998].

Chapter 5

(26) What does "ICD" stand for? [3]

ANS [International] [Classification] of [Disease]