USMLE USMLE Certifications USMLE-STEP-2 Questions & Answers

• Question 311:

  The laboratory test has a sensitivity of 85% and a specificity of 70%. You want to have 1000 persons take the test. To estimate the positive predictive value of the test for this population, you need to know which of the following?

  A. disease incidence

  B. disease prevalence

  C. negative predictive value

  D. the cut off values for the test

  E. the latest period of the disease

  Correct Answer: B

  In order to calculate predictive value, it is necessary to know prevalence. To illustrate this, onsider the extremes if prevalence is zero, positive predictive value will be zero, and negative predictive value will be 100%!

• Question 312:

  Doing a retrospective chart review of unmatched cases and controls, you calculate an OR to make an initial assessment of whether women who have had induced abortions are more likely to develop breast cancer. Twenty of 100 women with breast cancer reported a history of induced abortion. Ten of 200 women without breast cancer reported a history of induced abortion. What are the exposure odds among cases?

  A. 0.250

  B. 0.500

  C. 2.000

  D. 4.000

  E. 8.000

  Correct Answer: A

  The problem can be represented by the following table:

  

  The odds of exposure among cases is calculated by dividing the probability that a case was exposed by the probability that a case was not exposed: (20/100)/(80/100) = 20/80 = 0.25.

• Question 313:

  A new screening test for prostate cancer becomes available. You assess whether this will be useful to your practice by reviewing the operating characteristics of the test. The test's ability to correctly classify diseased persons as having disease is called what?

  A. specificity

  B. sensitivity

  C. positive predictive value

  D. negative predictive value

  E. reproducibility

  Correct Answer: B

  By definition, sensitivity is the probability of testing positive if the disease is truly present. It indicates the percentage of persons with the disease of interest who have positive test results. Positive predictive value estimates the probability of disease in those who have positive test results. It indicates the percentage of persons with positive test results who actually have the disease of interest.

• Question 314:

  On January 15, 2005, a health survey was performed in an elementary school of a developing country. All the school children were examined for conjunctivitis, and 2% of the children were diagnosed with the disease. From these data, one can determine which of the following?

  A. the incidence of conjunctivitis

  B. the prevalence of conjunctivitis

  C. both incidence and prevalence of conjunctivitis

  D. neither the incidence nor prevalence of conjunctivitis

  E. the attributable risk

  Correct Answer: B

  The health survey was conducted in a defined population on a particular date. With this information, the prevalence of conjunctivitis can be determined, but not the incidence. Measuring incidence requires information on new occurrences of the disease from a followup study.

• Question 315:

  You are reviewing a cohort (follow-up) study to determine whether dietary fiber reduces the risk of colon cancer. In the study, the population at risk at the beginning of the follow-up period should consist of which of the following?

  A. persons who all have diagnosed disease

  B. persons with diverse exposure levels and disease

  C. persons of comparable age, gender, and race

  D. persons with homogeneous disease probability

  E. persons who are susceptible but free of disease

  Correct Answer: E

  The design of a cohort study requires a follow-up of a group of subjects who are susceptible but free of the disease of interest at the beginning of the study period.

• Question 316:

  Among the observational study designs, the prospective cohort design offers which of the following advantages?

  A. It provides a relatively quick answer.

  B. It allows one to take advantage of existing outcome data.

  C. It is easy to assemble a comparison group.

  D. It allows one to measure incidence.

  E. It is relatively cheap.

  Correct Answer: D

  In a prospective cohort design, a group of subjects at risk of developing disease are followed over a specified period of time. This design permits the direct calculation of incidence by dividing the number of subjects who developed the disease of interest during the follow-up period by the population or persontime at risk. In contrast, incidence cannot be calculated directly from the other observational study design.

• Question 317:

  When making recommendations to a state general assembly against routine premarital screening, the State Health Commissioner used the following data to arrive at his conclusions. The state had a young adult population of 100,000. Their actual prevalence of human immunodeficiency virus (HIV) infection was 1 per 1000. The best screening test available had a sensitivity of 98% and a specificity of 95%. How many people in this population would have screened false positive?

  A. 4995

  B. 98

  C. 2

  D. 100

  E. 5000

  Correct Answer: A

  The following table was constructed using the data in the question. There would be 4995 FPs, 98 TPs, and 2 FNs.

  

• Question 318:

  Select the organism associated with the following clinical findings:

  Approximately 12 hours after a banquet, most of those who ate stew report abdominal cramps and diarrhea which subsided after 12 days.

  A. aureus

  B. beta-hemolytic Streptococcus

  C. respiratory syncytial virus (RSV)

  D. Mycoplasma pneumoniae

  E. Haemophilus pertussis

  F. Helicobacter pylori

  G. Escherichia coli

  H. Rickettsia prowazekii

  I. Giardia lamblia

  J. C. perfringens

  Correct Answer: J

  Giardiasis may cause cramping and a chronic diarrheal syndrome, with malabsorption and weight loss. Its distribution is worldwide, particularly where hygienic standards are not high. It also occurs sporadically in high-risk individuals. Streptococcal pyoderma, including erysipelas and impetigo, has been demonstrated to precede acute glomerulonephritis. Even when appropriate antibiotics are given in adequate dosage and duration for these conditions, renal damage may still result. Prevention thus consists of wound care, including cleaning wounds well and removal of crust. Mycoplasma infections are particularly common in families with younger children. They are frequently imported to the family by school-aged children, leading to a low-grade fever and persisting tracheobronchitis in the parents, or more acutely, an atypical pneumonia. G. lamblia is found in up to 20% of homosexual males, and may cause chronic diarrhea, although in these patients it tends to be asymptomatic. E. coli was first reported as a cause of watery diarrhea in nurseries in the 1940s. Although nursery epidemics with enteropathogenic serotypes had decreased in recent years in the United States, the increase of infant- child day care centers has resulted in their relatively frequent occurrence. Furunculosis is most frequently caused by coagulase-positive staphylococcal infections. The public health significance of this largely relates to the hazards of skin infections in food handlers and subsequent staphylococcal toxin in the food, leading to staphylococcal intoxication food-borne disease. H. pylori has been associated with gastric ulcers, but not with duodenal ulcers. Otitis media, whether acute or with effusion, commonly results from viral infection, such as by RSV. Various other organisms may be responsible including Streptococcu pneumoniae, H. influenzae, and others. C. perfringens, with rare exceptions, is transmitted in a meat dish prepared in bulk. Under propitious circumstances for the organism, especially on cooling of the food, bacterial multiplication can be very rapid. Symptoms begin to occur in the affected population in about 12 hours. Epidemic typhus is a rickettsial illness. Man is the host and long-term reservoir. The vectors are body lice (P. humanus corporis). The rickettsia are not present in human excretions and cannot be transmitted by person-toperson contact.

• Question 319:

  Select the organism associated with the following clinical findings:

  A2-year-old child is pulling on her earlobe and has a temperature of 39°C and a bulging eardrum.

  A. aureus

  B. beta-hemolytic Streptococcus

  C. respiratory syncytial virus (RSV)

  D. Mycoplasma pneumoniae

  E. Haemophilus pertussis

  F. Helicobacter pylori

  G. Escherichia coli

  H. Rickettsia prowazekii

  I. Giardia lamblia

  J. C. perfringens

  Correct Answer: C

  Giardiasis may cause cramping and a chronic diarrheal syndrome, with malabsorption and weight loss. Its distribution is worldwide, particularly where hygienic standards are not high. It also occurs sporadically in high-risk individuals. Streptococcal pyoderma, including erysipelas and impetigo, has been demonstrated to precede acute glomerulonephritis. Even when appropriate antibiotics are given in adequate dosage and duration for these conditions, renal damage may still result. Prevention thus consists of wound care, including cleaning wounds well and removal of crust. Mycoplasma infections are particularly common in families with younger children. They are frequently imported to the family by school-aged children, leading to a low-grade fever and persisting tracheobronchitis in the parents, or more acutely, an atypical pneumonia. G. lamblia is found in up to 20% of homosexual males, and may cause chronic diarrhea, although in these patients it tends to be asymptomatic. E. coli was first reported as a cause of watery diarrhea in nurseries in the 1940s. Although nursery epidemics with enteropathogenic serotypes had decreased in recent years in the United States, the increase of infant- child day care centers has resulted in their relatively frequent occurrence. Furunculosis is most frequently caused by coagulase-positive staphylococcal infections. The public health significance of this largely relates to the hazards of skin infections in food handlers and subsequent staphylococcal toxin in the food, leading to staphylococcal intoxication food-borne disease. H. pylori has been associated with gastric ulcers, but not with duodenal ulcers. Otitis media, whether acute or with effusion, commonly results from viral infection, such as by RSV. Various other organisms may be responsible including Streptococcu pneumoniae, H. influenzae, and others. C. perfringens, with rare exceptions, is transmitted in a meat dish prepared in bulk. Under propitious circumstances for the organism, especially on cooling of the food, bacterial multiplication can be very rapid. Symptoms begin to occur in the affected population in about 12 hours. Epidemic typhus is a rickettsial illness. Man is the host and long-term reservoir. The vectors are body lice (P. humanus corporis). The rickettsia are not present in human excretions and cannot be transmitted by person-toperson contact.

• Question 320:

  Select the organism associated with the following clinical findings:

  A50-year-old man who reports drinking two or three alcoholic beverages per day complains of chronic,

  vague, intermittent dyspepsia.

  A. aureus

  B. beta-hemolytic Streptococcus

  C. respiratory syncytial virus (RSV)

  D. Mycoplasma pneumoniae

  E. Haemophilus pertussis

  F. Helicobacter pylori

  G. Escherichia coli

  H. Rickettsia prowazekii

  I. Giardia lamblia

  J. C. perfringens

  Correct Answer: F

  Giardiasis may cause cramping and a chronic diarrheal syndrome, with malabsorption and weight loss. Its distribution is worldwide, particularly where hygienic standards are not high. It also occurs sporadically in high-risk individuals. Streptococcal pyoderma, including erysipelas and impetigo, has been demonstrated to precede acute glomerulonephritis. Even when appropriate antibiotics are given in adequate dosage and duration for these conditions, renal damage may still result. Prevention thus consists of wound care, including cleaning wounds well and removal of crust. Mycoplasma infections are particularly common in families with younger children. They are frequently imported to the family by school-aged children, leading to a low-grade fever and persisting tracheobronchitis in the parents, or more acutely, an atypical pneumonia. G. lamblia is found in up to 20% of homosexual males, and may cause chronic diarrhea, although in these patients it tends to be asymptomatic. E. coli was first reported as a cause of watery diarrhea in nurseries in the 1940s. Although nursery epidemics with enteropathogenic serotypes had decreased in recent years in the United States, the increase of infant- child day care centers has resulted in their relatively frequent occurrence. Furunculosis is most frequently caused by coagulase-positive staphylococcal infections. The public health significance of this largely relates to the hazards of skin infections in food handlers and subsequent staphylococcal toxin in the food, leading to staphylococcal intoxication food-borne disease. H. pylori has been associated with gastric ulcers, but not with duodenal ulcers. Otitis media, whether acute or with effusion, commonly results from viral infection, such as by RSV. Various other organisms may be responsible including Streptococcu pneumoniae, H. influenzae, and others. C. perfringens, with rare exceptions, is transmitted in a meat dish prepared in bulk. Under propitious circumstances for the organism, especially on cooling of the food, bacterial multiplication can be very rapid. Symptoms begin to occur in the affected population in about 12 hours. Epidemic typhus is a rickettsial illness. Man is the host and long-term reservoir. The vectors are body lice (P. humanus corporis). The rickettsia are not present in human excretions and cannot be transmitted by person-toperson contact.