Infectious Disease Practice Questions

Question 1

An 18-month-old boy presents to the emergency department for malaise. The boy’s parents report worsening fatigue for 3 days with associated irritability and anorexia. The patient’s newborn screening revealed a point mutation in the beta-globin gene but the patient has otherwise been healthy since birth. On physical exam, his temperature is 102.4°F (39.1°C), blood pressure is 78/42 mmHg, pulse is 124/min, and respirations are 32/min. The child is tired-appearing and difficult to soothe. Laboratory testing is performed and reveals the following:

Serum:
Na+: 137 mEq/L
Cl-: 100 mEq/L
K+: 4.4 mEq/L
HCO3-: 24 mEq/L
Urea nitrogen: 16 mg/dL
Creatinine: 0.9 mg/dL
Glucose: 96 mg/dL

Leukocyte count: 19,300/mm^3 with normal differential
Hemoglobin: 7.8 g/dL
Hematocrit: 21%
Mean corpuscular volume: 82 um^3
Platelet count: 324,000/mm^3
Reticulocyte index: 3.6%

Which of the following is the most likely causative organism for this patient's presentation?

Accepted Answer

Streptococcus pneumoniae

Answer

Listeria monocytogenes

Answer

Haemophilus influenzae

Answer

Neisseria meningitidis

Answer

Salmonella

Question 2

A 13-month-old boy is referred to an immunologist with recurrent otitis media, bacterial sinus infections, and pneumonia, which began several months earlier. He is healthy now, but the recurrent nature of these infections are troubling to his parents and they are hoping to find a definitive cause. The boy was born at 39 weeks gestation via spontaneous vaginal delivery. He is up to date on all vaccines and is meeting all developmental milestones. The patient has five older siblings, but none of them had similar recurrent illnesses. Clinical pathology results suggest very low levels of serum immunoglobulin. As you discuss options for diagnosis with the patient’s family, which of the following tests should be performed next?

Accepted Answer

Flow cytometry

Answer

CSF gram staining

Answer

Urine protein screening

Answer

Stool cultures

Answer

Genetic analysis

Question 3

A 12-month-old girl is brought to her pediatrician for a checkup and vaccines. The patient’s mother wants to send her to daycare but is worried about exposure to unvaccinated children and other potential sources of infection. The toddler was born at 39 weeks gestation via spontaneous vaginal delivery. She is up to date on all vaccines. She does not walk yet but stands in place and can say a few words. The toddler drinks formula and eats a mixture of soft vegetables and pureed meals. She has no current medications. On physical exam, the vital signs include: temperature 37.0°C (98.6°F), blood pressure 95/50 mm Hg, pulse 130/min, and respiratory rate 28/min. The patient is alert and responsive. The remainder of the exam is unremarkable. Which of the following is most appropriate for this patient at this visit?

Accepted Answer

MMR vaccine

Answer

Meningococcal vaccine

Answer

Gross motor workup and evaluation

Answer

Rotavirus vaccine

Answer

Referral for speech pathology

Question 4

A 30-year-old man is brought to the emergency department with complaints of fevers to 39.0℃ (102.2℉) and diarrhea for the past 12 hours. There is no history of headaches, vomiting, or loss of consciousness. The past medical history is unobtainable because the patient recently immigrated from abroad and has a language barrier, but his wife says that her husband had a motor vehicle accident when he was a teenager that required emergent surgery. He is transferred to the ICU after a few hours in the ED due to dyspnea, cyanosis, and hemodynamic collapse. There are no signs of a meningeal infection. The blood pressure is 70/30 mm Hg at the time of transfer. A chest X-ray at the time of admission shows interstitial infiltrates without homogeneous opacities. The initial laboratory results reveal metabolic acidosis, leukopenia with a count of 2000/mm3, thrombocytopenia (15,000/mm3), and a coagulation profile suggesting disseminated intravascular coagulation. A peripheral smear is performed as shown in the accompanying image. Despite ventilatory support, administration of intravenous fluids, antibiotics, and vasopressor agents, the patient dies the next day. The gram stain from the autopsy specimen of his lungs reveals gram-positive, lancet-shaped diplococci occurring singly and in chains. Which of the following organisms is the most likely cause for the patient’s condition?

Accepted Answer

Streptococcus pneumoniae

Answer

Neisseria meningitidis

Answer

Non-typeable H. influenzae

Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Question 5

A father brings his 3-year-old son to the pediatrician because he is concerned about his health. He states that throughout his son's life he has had recurrent infections despite proper treatment and hygiene. Upon reviewing the patient's chart, the pediatrician notices that the child has been infected multiple times with S. aureus, Aspergillus, and E. coli. Which of the following would confirm the most likely cause of this patient's symptoms?

Accepted Answer

Negative nitroblue-tetrazolium test

Answer

Increased IgM, Decreased IgG, IgA, and IgE

Answer

Positive nitroblue-tetrazolium test

Answer

Normal dihydrorhodamine (DHR) flow cytometry test

Answer

Increased IgE and IgA, Decreased IgM

Question 6

You are treating a neonate with meningitis using ampicillin and a second antibiotic, X, that is known to cause ototoxicity. What is the mechanism of antibiotic X?

Accepted Answer

It binds the 30S ribosomal subunit and inhibits formation of the initiation complex

Answer

It binds the 50S ribosomal subunit and inhibits formation of the initiation complex

Answer

It binds the 30S ribosomal subunit and reversibly inhibits translocation

Answer

It binds the 50S ribosomal subunit and inhibits peptidyltransferase

Answer

It binds the 50S ribosomal subunit and reversibly inhibits translocation

Question 7

You are seeing a 4-year-old boy in clinic who is presenting with concern for a primary immune deficiency. He has an unremarkable birth history, but since the age of 6 months he has had recurrent otitis media, bacterial pneumonia, as well as two episodes of sinusitis, and four episodes of conjunctivitis. He has a maternal uncle who died from sepsis secondary to H. influenza pneumonia. If you drew blood work for diagnostic testing, which of the following would you expect to find?

Accepted Answer

Abnormally low number of B cells

Answer

Abnormally low number of T cells

Answer

Abnormally high number of B cells

Answer

Elevated immunoglobulin levels

Answer

Abnormally high number of T cells

Question 8

A 4-year-old boy is brought to the emergency department by his parents. He is lethargic and confused and has a severe headache, vomiting, and a high-grade fever since earlier that day. His mother reports that the child was doing well until 2 days ago when he developed a fever and green nasal discharge. The patient has a history of neonatal sepsis, meningococcemia at 18 months of age, and pneumococcal pneumonia at 2 and 3 years of age. His scheduled vaccinations are up to date. His blood pressure is 70/50 mm Hg, heart rate is 120/min, respiratory rate is 22/min, and temperature is 39.3°C (102.4°F). On examination, the child is lethargic and his skin is pale, with several petechiae over his buttocks. There is a purulent nasal discharge from both nostrils. The lungs are clear to auscultation bilaterally. Heart sounds are normal. There is marked neck rigidity. Cerebrospinal fluid analysis shows the following results:
Opening pressure 100 mm H2O
Appearance cloudy
Protein 500 mg/dL (5 g/L)
White blood cells 2500/μL (polymorphonuclear predominance)
Glucose 31 mg/dL (1.7 mmol/L)
Culture positive for N. meningitidis
Which of the following immunological processes is most likely to be impaired in this child?

Accepted Answer

Formation of C5-9 complex

Answer

Production of IL-2 by Th1 cells

Answer

Oxidative burst in macrophages

Answer

Activation of TCRs by MHC-II

Answer

Cleavage of C2 component of complement into C2a and C2b

Question 9

A 10-year-old boy is brought to the emergency department by his parents because of a dull persistent headache beginning that morning. He has nausea and has vomited twice. During the past four days, the patient has had left-sided ear pain and fever, but his parents did not seek medical attention. He is from Thailand and is visiting his relatives in the United States for the summer. There is no personal or family history of serious illness. He is at the 45th percentile for height and 40th percentile for weight. He appears irritable. His temperature is 38.5°C (101.3°F), pulse is 110/min, and blood pressure is 98/58 mm Hg. The pupils are equal and reactive to light. Lateral gaze of the left eye is limited. The left tympanic membrane is erythematous with purulent discharge. There is no nuchal rigidity. Which of the following is the most appropriate next step in management?

Accepted Answer

MRI of the brain

Answer

Intravenous ceftriaxone and clindamycin therapy

Answer

Lumbar puncture

Answer

Intravenous cefazolin and metronidazole therapy

Answer

Cranial burr hole evacuation

Question 10

A 6-year-old girl is brought to the clinic for evaluation of malaise and low-grade fever over the past 3 days. In the last 24 hours, she developed sores and pain in her mouth. She also had vesicles on her hands and feet. Her past medical history was benign and the immunization history was up-to-date. The oral temperature was 38.1°C (100.6°F). The physical examination revealed several erythematous macules in the oropharynx and small oval vesicles with an erythematous base on the palms. What is the next best step in the management of this patient?

Accepted Answer

Supportive care

Answer

Corticosteroids

Answer

Penicillin

Answer

Ribavirin

Answer

Aspirin

Infectious Disease

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Common childhood exanthems

Pediatric respiratory infections

Pediatric gastrointestinal infections

Urinary tract infections in children

Bone and joint infections

Central nervous system infections

Pediatric tuberculosis

Pediatric HIV

Recurrent infections evaluation

Fever of unknown origin approach

Emerging infectious diseases in children

Post-infectious immune complications

Antimicrobial resistance in pediatrics

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About Infectious Disease for USMLE

Lessons in Infectious Disease

Master Infectious Disease