USMLE Step 2 Quiz
Practice Pediatric Infections in USMLE Step 2 with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.
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A 10-day-old newborn has poor feeding and irritability. Pregnancy and delivery were uncomplicated; mother reports painful genital lesions near delivery. Exam: temperature 38.3°C, vesicular lesions on scalp, lethargy. Labs: WBC 9,200/µL; AST elevated. CSF shows lymphocytic pleocytosis. Which of the following is the most appropriate next step in management?
This quiz focuses on Pediatric Infections, giving you a quick way to practice the rules, question types, and explanations that matter most for USMLE Step 2.
Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.
A 10-day-old newborn has poor feeding and irritability. Pregnancy and delivery were uncomplicated; mother reports painful genital lesions near delivery. Exam: temperature 38.3°C, vesicular lesions on scalp, lethargy. Labs: WBC 9,200/µL; AST elevated. CSF shows lymphocytic pleocytosis. Which of the following is the most appropriate next step in management?
Explanation: This question tests clinical knowledge of pediatric infections and decision-making skills as assessed in USMLE Step 2 CK. Understanding the differentiation between bacterial and viral infections is crucial for appropriate management. Bacterial infections often require antibiotics, whereas viral infections do not. In the vignette, the presence of vesicular lesions, maternal genital lesions, and CSF pleocytosis indicates neonatal HSV infection, guiding the clinician towards antiviral therapy and testing. The correct choice, A, aligns with clinical guidelines, ensuring effective treatment and improving patient outcomes. Option B is incorrect because it represents a common misconception such as treating viral HSV with bacterial antibiotics. To help students, emphasize recognizing key diagnostic indicators and adhering to guideline-based management. Practice differentiating similar presentations with different etiologies and understanding the implications of each choice.
A 6-year-old girl has 2 days of high fever, severe abdominal pain, and frequent bloody diarrhea after eating undercooked ground beef. Exam: diffuse abdominal tenderness; no peritoneal signs. Labs: WBC 15,600/µL; platelets normal; creatinine normal. Stool is positive for Shiga toxin. Which of the following is the most appropriate next step in management?
Explanation: This question tests clinical knowledge of pediatric infections and decision-making skills as assessed in USMLE Step 2 CK. Understanding the differentiation between bacterial and viral infections is crucial for appropriate management. Bacterial infections often require antibiotics, whereas viral infections do not. In the vignette, the presence of bloody diarrhea and positive Shiga toxin indicates EHEC infection, guiding the clinician towards supportive care to avoid complications. The correct choice, A, aligns with clinical guidelines, ensuring effective treatment and improving patient outcomes. Option B is incorrect because it represents a common misconception such as using antibiotics which may worsen HUS risk. To help students, emphasize recognizing key diagnostic indicators and adhering to guideline-based management. Practice differentiating similar presentations with different etiologies and understanding the implications of each choice.
A 2-day-old newborn has poor feeding, temperature instability, and lethargy. Pregnancy was complicated by prolonged rupture of membranes; mother’s GBS status is unknown. Exam: hypotonia, tachypnea, mottled skin; capillary refill 4 seconds. Labs: WBC 3,000/µL, ANC low; glucose 38 mg/dL; CRP elevated. Chest radiograph shows diffuse granular opacities. Which of the following is the most appropriate next step in management?
Explanation: This question tests clinical knowledge of pediatric infections and decision-making skills as assessed in USMLE Step 2 CK. Understanding the differentiation between bacterial and viral infections is crucial for appropriate management. Bacterial infections often require antibiotics, whereas viral infections do not. In the vignette, the presence of leukopenia, hypoglycemia, elevated CRP, and granular opacities on CXR indicates early-onset neonatal sepsis, guiding the clinician towards empiric antibiotics. The correct choice, A, aligns with clinical guidelines, ensuring effective treatment and improving patient outcomes. Option B is incorrect because it represents a common misconception such as assuming viral etiology in high-risk neonates. To help students, emphasize recognizing key diagnostic indicators and adhering to guideline-based management. Practice differentiating similar presentations with different etiologies and understanding the implications of each choice.
A 3-year-old boy presents with high fever, toxic appearance, and drooling. He sits leaning forward and refuses to lie down. Exam: inspiratory stridor, muffled voice; no cough. Lateral neck radiograph shows an enlarged epiglottis. Which of the following is the most appropriate next step in management?
Explanation: This question tests clinical knowledge of pediatric infections and decision-making skills as assessed in USMLE Step 2 CK. Understanding the differentiation between bacterial and viral infections is crucial for appropriate management. Bacterial infections often require antibiotics, whereas viral infections do not. In the vignette, the presence of drooling, stridor, and enlarged epiglottis on radiograph indicates epiglottitis, guiding the clinician towards airway security and antibiotics. The correct choice, B, aligns with clinical guidelines, ensuring effective treatment and improving patient outcomes. Option A is incorrect because it represents a common misconception such as risking airway compromise with examination. To help students, emphasize recognizing key diagnostic indicators and adhering to guideline-based management. Practice differentiating similar presentations with different etiologies and understanding the implications of each choice.
A 5-year-old girl has fever and cough after daycare exposure. She develops a nonblanching petechial rash on the legs and becomes lethargic. Exam: tachycardia, delayed capillary refill, nuchal rigidity. Labs: WBC 18,500/µL; platelets 90,000/µL; lactate elevated. What is the most appropriate next step in management?
Explanation: This question tests clinical knowledge of pediatric infections and decision-making skills as assessed in USMLE Step 2 CK. Understanding the differentiation between bacterial and viral infections is crucial for appropriate management. Bacterial infections often require antibiotics, whereas viral infections do not. In the vignette, the presence of petechial rash, lethargy, nuchal rigidity, and elevated lactate indicates meningococcemia, guiding the clinician towards immediate empiric antibiotics. The correct choice, B, aligns with clinical guidelines, ensuring effective treatment and improving patient outcomes. Option E is incorrect because it represents a common misconception such as assuming viral etiology despite signs of sepsis. To help students, emphasize recognizing key diagnostic indicators and adhering to guideline-based management. Practice differentiating similar presentations with different etiologies and understanding the implications of each choice.
A 3-year-old girl with cough and fever has decreased breath sounds and dullness to percussion on the right. Exam: tachypnea and mild retractions. Labs: WBC 20,100/µL with neutrophil predominance. Chest radiograph shows a right pleural effusion with adjacent consolidation. Which of the following is the most appropriate next step in management?
Explanation: This question tests clinical knowledge of pediatric infections and decision-making skills as assessed in USMLE Step 2 CK. Understanding the differentiation between bacterial and viral infections is crucial for appropriate management. Bacterial infections often require antibiotics, whereas viral infections do not. In the vignette, the presence of pleural effusion with consolidation and neutrophil predominance indicates complicated bacterial pneumonia, guiding the clinician towards drainage and antibiotics. The correct choice, B, aligns with clinical guidelines, ensuring effective treatment and improving patient outcomes. Option D is incorrect because it represents a common misconception such as assuming viral etiology in bacterial complication. To help students, emphasize recognizing key diagnostic indicators and adhering to guideline-based management. Practice differentiating similar presentations with different etiologies and understanding the implications of each choice.
A 5-year-old girl has fever and sore throat for 2 days after a daycare outbreak. She now has a fine, sandpaper-like rash on the trunk and erythematous oropharynx with palatal petechiae. Exam: tender anterior cervical nodes, no cough. Labs: WBC 14,800/µL with neutrophil predominance; CRP elevated. Rapid antigen detection test for group A strep is positive. What is the first-line treatment for this infection?
Explanation: This question tests clinical knowledge of pediatric infections and decision-making skills as assessed in USMLE Step 2 CK. Understanding the differentiation between bacterial and viral infections is crucial for appropriate management. Bacterial infections often require antibiotics, whereas viral infections do not. In the vignette, the presence of sandpaper-like rash, palatal petechiae, and positive rapid strep test indicates scarlet fever from group A streptococcus, guiding the clinician towards antibiotic therapy. The correct choice, A, aligns with clinical guidelines, ensuring effective treatment and improving patient outcomes. Option D is incorrect because it represents a common misconception such as misidentifying bacterial pharyngitis as viral and withholding antibiotics. To help students, emphasize recognizing key diagnostic indicators and adhering to guideline-based management. Practice differentiating similar presentations with different etiologies and understanding the implications of each choice.
A 3-week-old female infant is brought to the emergency department by her mother due to a rectal temperature of 38.5°C (101.3°F), poor feeding for the past 12 hours, and increased irritability. The infant was born full-term via an uncomplicated vaginal delivery and has been meeting developmental milestones. On examination, she is fussy but consolable. Her anterior fontanelle is soft and flat. Lungs are clear to auscultation, and there is no heart murmur. The remainder of the examination is unremarkable. She has no signs of localized infection.
Which of the following is the most appropriate next step in the management of this patient?
Explanation: This infant is under 28 days old and presents with a fever, which constitutes a medical emergency. Neonates with fever are at high risk for serious bacterial infection (SBI), including sepsis, meningitis, and urinary tract infection. Standard of care requires a full septic workup, including blood, urine, and cerebrospinal fluid (CSF) cultures, followed by the immediate administration of empiric intravenous antibiotics (typically ampicillin and gentamicin or cefotaxime). Hospital admission is mandatory. Delaying treatment pending laboratory results can lead to significant morbidity and mortality.
An 18-month-old boy is brought to the clinic for a 2-day history of fever, irritability, and pulling at his right ear. He has had a runny nose for the past week. His immunizations are up to date. On physical examination, his temperature is 38.8°C (101.8°F). Otoscopic examination of the right ear reveals a bulging, erythematous tympanic membrane with loss of landmarks and poor mobility on pneumatic otoscopy. The left ear is normal.
Which of the following is the most appropriate initial treatment for this patient's condition?
Explanation: The patient's presentation of fever, ear pain, and a bulging, erythematous tympanic membrane is classic for acute otitis media (AOM). For children under 2 years of age with a certain diagnosis of AOM, antibiotics are recommended. High-dose amoxicillin is the first-line treatment due to its efficacy against the most common causative organisms (Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis), safety profile, and narrow spectrum. Amoxicillin-clavulanate is reserved for patients who have received amoxicillin in the past 30 days, have concurrent purulent conjunctivitis, or have a history of recurrent AOM. Observation is an option for older children (>2 years) with non-severe, unilateral AOM. Azithromycin is not a first-line agent due to high rates of pneumococcal resistance.
A 6-week-old infant is brought to the emergency department due to lethargy and fever of 39.0°C (102.2°F). On examination, the infant is difficult to arouse and has a bulging anterior fontanelle. A lumbar puncture is performed. Cerebrospinal fluid analysis shows a WBC count of 1500/mm³ with 85% neutrophils, a glucose level of 20 mg/dL (serum glucose is 90 mg/dL), and a protein level of 250 mg/dL.
Which of the following is the most likely causative organism?
Explanation: The clinical presentation and CSF findings are consistent with bacterial meningitis. In an infant between 1 and 3 months of age, the most common causes of bacterial meningitis are Streptococcus agalactiae (Group B Streptococcus), Escherichia coli, and Listeria monocytogenes. GBS is the leading cause in this age group, typically acquired perinatally. Listeria is also a consideration, which is why ampicillin is included in empiric therapy. Neisseria meningitidis and Streptococcus pneumoniae become more common causes of meningitis after 3 months of age, once maternal antibody protection wanes and the infant is more exposed to the community.
A 2-year-old toilet-trained girl presents with a 2-day history of fever, fussiness, and new-onset urinary incontinence. She had a similar episode 6 months ago that was treated with antibiotics. A catheterized urine specimen is obtained. Urinalysis is positive for leukocyte esterase and nitrites. Urine culture is pending. She is started on an appropriate oral antibiotic.
Which of the following is the most appropriate next step in the evaluation of this patient?
Explanation: Current guidelines for febrile urinary tract infections (UTIs) in children aged 2 to 24 months recommend a renal and bladder ultrasound (RBUS) for all patients after their first episode to evaluate for anatomic abnormalities such as hydronephrosis or renal abscess. Given this child's age and history of a recurrent UTI, an RBUS is definitely indicated. A voiding cystourethrogram (VCUG) is typically reserved for children who have abnormalities on the RBUS or for those with recurrent febrile UTIs, to evaluate for vesicoureteral reflux. Admission for IV antibiotics is only necessary if the child is toxic-appearing, dehydrated, or unable to tolerate oral medications. No further workup would be inappropriate given the recurrence.
A 3-month-old infant, who has not received any immunizations, is brought to the clinic with a 2-week history of worsening cough. The mother describes episodes where the infant coughs repeatedly until she turns red in the face, followed by a loud gasp for air. Some episodes are followed by vomiting. Between episodes, the infant appears well. A complete blood count reveals a WBC of 25,000/mm³ with 70% lymphocytes.
Which of the following is the most appropriate test to confirm the diagnosis?
Explanation: The clinical presentation of paroxysmal cough, inspiratory whoop, and post-tussive emesis in an unimmunized infant, along with marked lymphocytosis, is highly suggestive of pertussis (whooping cough). The gold standard for diagnosis in the early stages of the illness (first 2-3 weeks) is polymerase chain reaction (PCR) testing of a nasopharyngeal swab or aspirate for Bordetella pertussis. Culture can also be used but is less sensitive. Chest x-ray is often normal or may show perihilar infiltrates but is not diagnostic. Blood cultures would be negative, and obtaining a sputum sample from an infant is not feasible.
An 11-month-old girl is brought to the clinic by her parents. They report she had a high fever, up to 40.0°C (104.0°F), for the past 3 days. During this time, she was irritable but otherwise seemed well. This morning, her fever broke, and she subsequently developed a pink, maculopapular rash that started on her chest and back and is now spreading to her neck and arms. On examination, she is afebrile, alert, and playful. The rash blanches with pressure.
What is the most likely diagnosis?
Explanation: This is a classic presentation of roseola infantum (also known as exanthem subitum or sixth disease), which is caused by Human herpesvirus 6. It is characterized by 3-5 days of high fever in a well-appearing child, followed by defervescence and the subsequent eruption of a maculopapular rash that starts on the trunk and spreads outwards. Measles presents with a prodrome of cough, coryza, and conjunctivitis before the rash. Rubella has a similar rash but is associated with postauricular lymphadenopathy and a lower fever. Erythema infectiosum presents with a "slapped cheek" rash.
A 6-year-old girl is diagnosed with streptococcal pharyngitis. Two days after starting amoxicillin, she develops a fever, diffuse erythematous rash that feels like sandpaper, and a bright red tongue with prominent papillae. On examination, the rash is most prominent in the skin folds of the axilla and groin. There is also pallor around her mouth.
This patient's rash is caused by a toxin produced by an organism that is also a common cause of which of the following conditions?
Explanation: The patient's presentation is classic for scarlet fever, which is caused by an erythrogenic toxin-producing strain of Group A Streptococcus (GAS), the same organism that causes streptococcal pharyngitis. GAS infections can lead to delayed, non-suppurative complications, including acute rheumatic fever and post-streptococcal glomerulonephritis. Coronary artery aneurysms are a complication of Kawasaki disease. Aplastic crisis is a potential complication of Parvovirus B19 infection in patients with underlying hemoglobinopathies. Subacute sclerosing panencephalitis is a rare, late complication of measles.
A 4-year-old boy presents with a 2-day history of high fever and refusal to walk. His parents note that any attempt to move his left leg causes him to cry in pain. On physical examination, his temperature is 39.5°C (103.1°F). His left hip is held in a flexed, abducted, and externally rotated position. There is exquisite pain with passive internal rotation of the hip. Laboratory studies show a WBC of 18,000/mm³ and an ESR of 80 mm/hr.
Which of the following is the most appropriate next step to confirm the diagnosis?
Explanation: The clinical picture is highly suspicious for septic arthritis of the hip, which is a surgical emergency. The definitive diagnosis is made by aspirating synovial fluid from the joint and analyzing it for cell count, Gram stain, and culture. Ultrasound is the imaging modality of choice to identify a joint effusion and to guide needle aspiration. Plain radiographs are often normal early in the course of septic arthritis but can help rule out other conditions. While an MRI is very sensitive, it is often not necessary for diagnosis and can delay treatment. Empiric antibiotics should be started, but only after joint fluid has been obtained for culture, as pre-treatment can sterilize the culture and obscure the diagnosis.
A 2-year-old girl attending daycare is brought to the clinic with a 3-day history of low-grade fever, fussiness, and poor appetite. On examination, there are several shallow ulcers on her tongue and buccal mucosa. She also has a non-pruritic rash on her hands and feet, characterized by small, greyish vesicles on an erythematous base.
Which of the following is the most appropriate management for this patient?
Explanation: The patient's presentation of oral ulcers and a vesicular rash on the hands and feet is classic for Hand, Foot, and Mouth Disease (HFMD). This is a common, self-limited viral illness, most often caused by Coxsackievirus A16. Management is entirely supportive, focusing on maintaining hydration (as oral ulcers can be painful) and providing pain and fever control with acetaminophen or ibuprofen. Antivirals like acyclovir (for herpesviruses) and antibiotics like amoxicillin are not effective against coxsackievirus. Topical corticosteroids are not indicated and may be harmful.
A 15-month-old girl who is fully up to date on her immunizations is brought to the office with a temperature of 39.4°C (102.9°F) for the past 24 hours. Her parents report she is slightly less active but is still drinking fluids well and has had several wet diapers. On examination, she is alert and interactive. Her physical examination, including ears, throat, lungs, and abdomen, is entirely normal. A catheterized urinalysis is negative.
Which of the following is the most appropriate next step in management?
Explanation: This is a well-appearing, fully immunized child between 3 and 36 months of age with a fever without a source. The widespread use of vaccines against H. influenzae type b and S. pneumoniae has dramatically reduced the risk of occult bacteremia in this population. For a well-appearing, immunized child with a negative urinalysis, current guidelines support a strategy of observation with symptomatic care (antipyretics) and close follow-up. A full septic workup or empiric antibiotics are not indicated unless the child appears toxic or develops signs of a focal infection.
A 4-year-old boy whose parents have declined vaccinations is brought to the emergency department with acute respiratory distress. He developed a high fever, sore throat, and muffled voice over the past few hours. He is sitting upright, leaning forward, and drooling. Inspiratory stridor is noted. He appears anxious and toxic.
Which of the following is the most appropriate initial action?
Explanation: This patient's presentation (high fever, drooling, dysphagia, distress, tripod position) is classic for epiglottitis, a life-threatening infection typically caused by Haemophilus influenzae type b. The primary concern is impending airway obstruction. The most critical initial action is to secure the patient's airway. This should be done in a controlled setting, such as an operating room, with personnel skilled in pediatric airway management (anesthesiology and otolaryngology) present. Any attempt to examine the oropharynx or cause the child distress (e.g., by obtaining an X-ray or starting an IV) could precipitate laryngospasm and complete airway obstruction. While antibiotics are necessary, they are administered only after the airway is secured.
A 3-year-old girl presents with a 4-day history of low-grade fever and cough. The cough began as dry but is now productive. On examination, she is afebrile and in no respiratory distress. Auscultation reveals diffuse bilateral wheezing and coarse rhonchi that clear with coughing. A chest x-ray shows prominent peribronchial markings but no focal consolidation.
What is the most likely diagnosis?
Explanation: The patient's symptoms of cough and wheezing following an upper respiratory infection, in the absence of significant respiratory distress or focal lung findings, are most consistent with acute bronchitis. The chest x-ray findings of peribronchial thickening are also characteristic. Acute bronchitis in this age group is almost always viral. Bacterial pneumonia would typically present with higher fever, more significant respiratory distress, and a focal consolidation on chest x-ray. While this could be a first-time wheezing episode related to a virus, the term acute bronchitis is the most fitting diagnosis. Bronchiolitis is typically seen in children under 2 years of age.
A 6-year-old boy is brought to the clinic in the spring with a rash. His mother reports he had a low-grade fever and felt mildly unwell a few days ago. On examination, he has bright red erythema on his cheeks, giving a "slapped cheek" appearance. He also has a faint, pink, reticular (lacy) rash on his trunk and extremities. He is otherwise well-appearing and his joint examination is normal.
This patient's condition is caused by which of the following viruses?
Explanation: The classic presentation of a "slapped cheek" rash followed by a lacy, reticular rash on the body is pathognomonic for erythema infectiosum, also known as fifth disease. This condition is caused by Parvovirus B19. Human herpesvirus 6 causes roseola infantum (high fever followed by rash). Coxsackievirus causes hand, foot, and mouth disease. Measles virus causes a prodrome of fever and the three 'C's (cough, coryza, conjunctivitis) followed by a morbilliform rash spreading from head to toe.