USMLE Step 1 Clinical Science Review: Integrated Practice Quiz
This practice quiz is designed for medical students preparing for the USMLE Step 1
examination. It emphasizes the integration of clinical presentations with foundational
principles of microbiology, pharmacology, immunology, and endocrinology.
Question 1
A 1-week-old neonate is brought to the pediatric clinic for a follow-up. The mother reports the
infant has been irritable, feeding poorly, and passing frequent loose stools. Physical
examination shows a fussy infant with a temperature of 37.9°C (100.2°F), heart rate of
158/min, and blood pressure of 62/40 mmHg. Abdominal examination reveals mild
distension. A biopsy of the colonic mucosa shows hyperemic tissue with enlarged
endothelial and stromal cells containing prominent intranuclear "owl’s eye" (Baykuş gözü)
inclusions.What is the most likely causative agent?A) Human papillomavirus (HPV) Type
16 B) Mycobacterium bovis C) Cytomegalovirus (CMV) D) Echinococcus granulosus E)
Treponema pallidumExplanation:Correct Answer: C) Cytomegalovirus (CMV). The
clinical presentation of neonatal irritability and diarrhea, combined with the classic
histopathological finding of "owl’s eye" inclusions (large intranuclear inclusions surrounded
by a clear halo) in stromal and endothelial cells, is diagnostic of CMV infection. CMV is a
major cause of congenital and neonatal morbidity.
● Choice A is incorrect. HPV-16 is a double-stranded DNA virus associated with
warts and cervical/anogenital malignancies, not neonatal gastrointestinal illness with
systemic viral inclusions.
● Choice B is incorrect. M. bovis causes a granulomatous tuberculosis-like illness.
It is characterized by acid-fast bacilli and granuloma formation, not viral inclusions.
● Choice D is incorrect. Echinococcus granulosus is a helminth that causes hydatid
cyst disease, typically manifesting as large fluid-filled cysts in the liver or lungs.
● Choice E is incorrect. Congenital syphilis ( T. pallidum ) presents with snuffles,
notched teeth, or bone abnormalities (saber shins), and tertiary syphilis presents later
with gummas. It does not produce cellular viral inclusions.
Question 2
A 54-year-old male is hospitalized for an invasive fungal infection. He is started on an
intravenous antifungal agent. Two days later, his temperature is 37.0°C (98.6°F), blood
pressure is 128/82 mmHg, and heart rate is 74/min. He reports new-onset blurred vision and
a "bluish tint" to his surroundings. An electrocardiogram (ECG) is performed and reveals a
QTc interval of 510 msec (baseline 430 msec).Which of the following medications is
most likely responsible for these findings?A) Ketoconazole B) Posaconazole C)
Fluconazole D) Itraconazole E) VoriconazoleExplanation:Correct Answer: E)
Voriconazole. Voriconazole is a second-generation triazole used for invasive aspergillosis.
It is uniquely associated with transient visual disturbances (blurred vision, photophobia, or
altered color perception) in about 30% of patients. Additionally, like other azoles, it can
cause QTc prolongation.
● Choice A is incorrect. Ketoconazole is primarily used for Cushing syndrome or
topical fungal infections due to its high side-effect profile, including significant
CYP450 inhibition and inhibition of testosterone synthesis (gynecomastia). It does
not cause visual changes.
, ● Choice B is incorrect. Posaconazole has a broad spectrum of activity and can
cause QTc prolongation, but it is not associated with the visual disturbances
described.
● Choice C is incorrect. Fluconazole is commonly used for Candida and
Cryptococcus but is rarely associated with visual changes or significant QTc
prolongation compared to the other options.
● Choice D is incorrect. Itraconazole is used for dimorphic fungi but is notable for
negative inotropic effects (avoid in heart failure) rather than visual disturbances.
Question 3
A 32-year-old pregnant woman at 32 weeks gestation presents to her obstetrician with
dysuria and increased urinary frequency. Her temperature is 37.2°C (99.0°F), BP 118/74
mmHg, and HR 82/min. A urine culture grows beta-hemolytic, Gram-positive cocci in chains.
The laboratory reports that the organism is CAMP (Christie-Atkins-Munch-Peterson) test
positive.What is the most likely pathogen?A) Enterococcus faecium B) Staphylococcus
saprophyticus C) Enterococcus faecalis D) Streptococcus agalactiae E) Streptococcus
pyogenesExplanation:Correct Answer: D) Streptococcus agalactiae . Streptococcus
agalactiae (Group B Streptococcus) is a common colonizer of the female genitourinary tract.
It is characterized by beta-hemolysis and a positive CAMP test (which identifies the CAMP
factor that enlarges the zone of hemolysis produced by S. aureus ). It is a leading cause of
UTI in pregnancy and neonatal sepsis.
● Choices A and C are incorrect. Enterococcus species are generally
gamma-hemolytic and are inhibited by bile and 6.5% NaCl. They do not produce a
positive CAMP test.
● Choice B is incorrect. S. saprophyticus is a common cause of UTIs in young
women but is a Gram-positive coccus in clusters (Catalase-positive) and is not
beta-hemolytic.
● Choice E is incorrect. Streptococcus pyogenes (Group A Strep) is beta-hemolytic
but is CAMP test negative and Bacitracin sensitive.
Question 4
A 3-year-old male is brought to the emergency department for evaluation of lower extremity
weakness. He has a significant history of recurrent sinopulmonary infections since age 6
months. His mother notes he received a live-attenuated oral polio vaccine two weeks ago.
Physical examination reveals asymmetric flaccid paralysis and absent deep tendon reflexes
in the left leg.Which underlying immunodeficiency is the most likely cause of this
patient’s presentation?A) Complement deficiency B) Severe Combined Immunodeficiency
(SCID) C) Chronic Granulomatous Disease (CGD) D) Bruton agammaglobulinemia E)
Secondary immunodeficiencyExplanation:Correct Answer: D) Bruton
agammaglobulinemia. Also known as X-linked agammaglobulinemia (XLA), this condition
involves a defect in Bruton Tyrosine Kinase (BTK), preventing B-cell maturation. Patients
lack all classes of immunoglobulins. They are susceptible to encapsulated bacteria and
certain viral infections. Crucially, they lack mucosal IgA, allowing live-attenuated polio virus
(Sabin vaccine) to revert to virulence and cause paralytic disease.
● Choice A is incorrect. Complement deficiencies (e.g., C5-C9) predispose patients
to Neisseria infections, not paralysis from live-attenuated vaccines.
This practice quiz is designed for medical students preparing for the USMLE Step 1
examination. It emphasizes the integration of clinical presentations with foundational
principles of microbiology, pharmacology, immunology, and endocrinology.
Question 1
A 1-week-old neonate is brought to the pediatric clinic for a follow-up. The mother reports the
infant has been irritable, feeding poorly, and passing frequent loose stools. Physical
examination shows a fussy infant with a temperature of 37.9°C (100.2°F), heart rate of
158/min, and blood pressure of 62/40 mmHg. Abdominal examination reveals mild
distension. A biopsy of the colonic mucosa shows hyperemic tissue with enlarged
endothelial and stromal cells containing prominent intranuclear "owl’s eye" (Baykuş gözü)
inclusions.What is the most likely causative agent?A) Human papillomavirus (HPV) Type
16 B) Mycobacterium bovis C) Cytomegalovirus (CMV) D) Echinococcus granulosus E)
Treponema pallidumExplanation:Correct Answer: C) Cytomegalovirus (CMV). The
clinical presentation of neonatal irritability and diarrhea, combined with the classic
histopathological finding of "owl’s eye" inclusions (large intranuclear inclusions surrounded
by a clear halo) in stromal and endothelial cells, is diagnostic of CMV infection. CMV is a
major cause of congenital and neonatal morbidity.
● Choice A is incorrect. HPV-16 is a double-stranded DNA virus associated with
warts and cervical/anogenital malignancies, not neonatal gastrointestinal illness with
systemic viral inclusions.
● Choice B is incorrect. M. bovis causes a granulomatous tuberculosis-like illness.
It is characterized by acid-fast bacilli and granuloma formation, not viral inclusions.
● Choice D is incorrect. Echinococcus granulosus is a helminth that causes hydatid
cyst disease, typically manifesting as large fluid-filled cysts in the liver or lungs.
● Choice E is incorrect. Congenital syphilis ( T. pallidum ) presents with snuffles,
notched teeth, or bone abnormalities (saber shins), and tertiary syphilis presents later
with gummas. It does not produce cellular viral inclusions.
Question 2
A 54-year-old male is hospitalized for an invasive fungal infection. He is started on an
intravenous antifungal agent. Two days later, his temperature is 37.0°C (98.6°F), blood
pressure is 128/82 mmHg, and heart rate is 74/min. He reports new-onset blurred vision and
a "bluish tint" to his surroundings. An electrocardiogram (ECG) is performed and reveals a
QTc interval of 510 msec (baseline 430 msec).Which of the following medications is
most likely responsible for these findings?A) Ketoconazole B) Posaconazole C)
Fluconazole D) Itraconazole E) VoriconazoleExplanation:Correct Answer: E)
Voriconazole. Voriconazole is a second-generation triazole used for invasive aspergillosis.
It is uniquely associated with transient visual disturbances (blurred vision, photophobia, or
altered color perception) in about 30% of patients. Additionally, like other azoles, it can
cause QTc prolongation.
● Choice A is incorrect. Ketoconazole is primarily used for Cushing syndrome or
topical fungal infections due to its high side-effect profile, including significant
CYP450 inhibition and inhibition of testosterone synthesis (gynecomastia). It does
not cause visual changes.
, ● Choice B is incorrect. Posaconazole has a broad spectrum of activity and can
cause QTc prolongation, but it is not associated with the visual disturbances
described.
● Choice C is incorrect. Fluconazole is commonly used for Candida and
Cryptococcus but is rarely associated with visual changes or significant QTc
prolongation compared to the other options.
● Choice D is incorrect. Itraconazole is used for dimorphic fungi but is notable for
negative inotropic effects (avoid in heart failure) rather than visual disturbances.
Question 3
A 32-year-old pregnant woman at 32 weeks gestation presents to her obstetrician with
dysuria and increased urinary frequency. Her temperature is 37.2°C (99.0°F), BP 118/74
mmHg, and HR 82/min. A urine culture grows beta-hemolytic, Gram-positive cocci in chains.
The laboratory reports that the organism is CAMP (Christie-Atkins-Munch-Peterson) test
positive.What is the most likely pathogen?A) Enterococcus faecium B) Staphylococcus
saprophyticus C) Enterococcus faecalis D) Streptococcus agalactiae E) Streptococcus
pyogenesExplanation:Correct Answer: D) Streptococcus agalactiae . Streptococcus
agalactiae (Group B Streptococcus) is a common colonizer of the female genitourinary tract.
It is characterized by beta-hemolysis and a positive CAMP test (which identifies the CAMP
factor that enlarges the zone of hemolysis produced by S. aureus ). It is a leading cause of
UTI in pregnancy and neonatal sepsis.
● Choices A and C are incorrect. Enterococcus species are generally
gamma-hemolytic and are inhibited by bile and 6.5% NaCl. They do not produce a
positive CAMP test.
● Choice B is incorrect. S. saprophyticus is a common cause of UTIs in young
women but is a Gram-positive coccus in clusters (Catalase-positive) and is not
beta-hemolytic.
● Choice E is incorrect. Streptococcus pyogenes (Group A Strep) is beta-hemolytic
but is CAMP test negative and Bacitracin sensitive.
Question 4
A 3-year-old male is brought to the emergency department for evaluation of lower extremity
weakness. He has a significant history of recurrent sinopulmonary infections since age 6
months. His mother notes he received a live-attenuated oral polio vaccine two weeks ago.
Physical examination reveals asymmetric flaccid paralysis and absent deep tendon reflexes
in the left leg.Which underlying immunodeficiency is the most likely cause of this
patient’s presentation?A) Complement deficiency B) Severe Combined Immunodeficiency
(SCID) C) Chronic Granulomatous Disease (CGD) D) Bruton agammaglobulinemia E)
Secondary immunodeficiencyExplanation:Correct Answer: D) Bruton
agammaglobulinemia. Also known as X-linked agammaglobulinemia (XLA), this condition
involves a defect in Bruton Tyrosine Kinase (BTK), preventing B-cell maturation. Patients
lack all classes of immunoglobulins. They are susceptible to encapsulated bacteria and
certain viral infections. Crucially, they lack mucosal IgA, allowing live-attenuated polio virus
(Sabin vaccine) to revert to virulence and cause paralytic disease.
● Choice A is incorrect. Complement deficiencies (e.g., C5-C9) predispose patients
to Neisseria infections, not paralysis from live-attenuated vaccines.
