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ABP Pediatric Infectious Diseases study materials
ABP Pediatric Infectious Diseases study resources

ABP Pediatric Infectious Diseases practice questions

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Question 1Bacterial Infections and Mycobacterial Disease

A 6-day-old term infant develops fever, poor feeding, and lethargy. Blood and cerebrospinal fluid cultures are obtained. Which empiric antibiotic regimen is most appropriate while awaiting results?

  1. Ceftriaxone alone
  2. Vancomycin plus meropenem
  3. Azithromycin plus ceftriaxone
  4. Ampicillin plus gentamicin Correct answer.

Explanation

Empiric therapy for neonatal sepsis must cover group B Streptococcus, Listeria monocytogenes, and enteric gram-negative bacilli, which is achieved with ampicillin plus an aminoglycoside. Ceftriaxone is generally avoided in neonates because it displaces bilirubin from albumin and can precipitate with calcium-containing fluids.

Question 2Bacterial Infections and Mycobacterial Disease

A 9-year-old has a positive rapid antigen test for group A Streptococcus and no drug allergies. Which oral antibiotic is the first-line treatment?

  1. Amoxicillin Correct answer.
  2. Azithromycin
  3. Doxycycline
  4. Trimethoprim-sulfamethoxazole

Explanation

Penicillin and amoxicillin remain first-line because group A Streptococcus has never developed confirmed penicillin resistance, and these agents are narrow-spectrum and inexpensive. A 10-day course of oral amoxicillin is standard for eradication and prevention of rheumatic fever.

Question 3Bacterial Infections and Mycobacterial Disease

A 6-week-old infant has paroxysmal cough with a whoop and post-tussive emesis, and pertussis is confirmed by PCR. Which antibiotic is the preferred treatment?

  1. Trimethoprim-sulfamethoxazole
  2. Amoxicillin
  3. Doxycycline
  4. Azithromycin Correct answer.

Explanation

Macrolides are the drugs of choice for pertussis, and azithromycin is preferred in young infants because of once-daily dosing and good tolerability. Treatment eradicates the organism and reduces transmission, although it does not reverse symptoms that are already established.

Question 4Bacterial Infections and Mycobacterial Disease

A 6-year-old child's older sibling is hospitalized with meningococcal meningitis and did not receive chemoprophylaxis. Which medication is appropriate prophylaxis for the 6-year-old?

  1. Rifampin Correct answer.
  2. Azithromycin
  3. Amoxicillin
  4. Penicillin G

Explanation

Household contacts of a patient with invasive meningococcal disease should receive chemoprophylaxis with rifampin, ciprofloxacin, or ceftriaxone to eradicate nasopharyngeal carriage. Prophylaxis should be given as soon as possible, ideally within 24 hours of identifying the index case.

Question 5Bacterial Infections and Mycobacterial Disease

Which organism is the most common cause of acute hematogenous osteomyelitis in children older than 3 years?

  1. Kingella kingae
  2. Staphylococcus aureus Correct answer.
  3. Salmonella enterica
  4. Streptococcus pneumoniae

Explanation

Staphylococcus aureus causes the majority of acute hematogenous bone infections at essentially all pediatric ages beyond the neonatal period. Salmonella is characteristically associated with sickle cell disease rather than being the usual pathogen in healthy children.

Question 6Bacterial Infections and Mycobacterial Disease

A 4-year-old develops a single expanding erythema migrans lesion after a tick bite in an endemic area, without fever or neurologic symptoms. Which oral regimen is appropriate?

  1. Amoxicillin for 14 days Correct answer.
  2. Intravenous ceftriaxone for 14 days
  3. Azithromycin for 5 days
  4. Cephalexin for 10 days

Explanation

Early localized Lyme disease is treated orally with amoxicillin, doxycycline, or cefuroxime axetil, and amoxicillin is a standard choice in young children. Parenteral therapy is reserved for disseminated disease with neurologic, cardiac, or severe joint involvement.

Question 7Bacterial Infections and Mycobacterial Disease

A 3-year-old has 2 weeks of fever and vomiting followed by seizures. Cerebrospinal fluid shows lymphocytic pleocytosis, low glucose, and high protein, and the family recently emigrated from a country with high tuberculosis prevalence. Which initial regimen is most appropriate?

  1. Ceftriaxone plus vancomycin for 14 days
  2. Isoniazid, rifampin, and ethambutol without steroids
  3. Isoniazid and rifampin alone for 12 months
  4. Isoniazid, rifampin, pyrazinamide, ethambutol, and steroids Correct answer.

Explanation

Tuberculous meningitis is treated initially with four drugs - isoniazid, rifampin, pyrazinamide, and ethambutol - because of the risk of resistance and the severity of the disease. Adjunctive corticosteroids improve survival and reduce neurologic sequelae.

Question 8Bacterial Infections and Mycobacterial Disease

A 5-year-old who recently immigrated has a positive interferon-gamma release assay, a normal chest radiograph, no symptoms, and a normal examination. Which management is indicated?

  1. Isoniazid plus rifampin for 2 weeks
  2. No treatment, with repeat testing in 1 year
  3. Isoniazid alone for 6 to 9 months Correct answer.
  4. Four-drug therapy for 6 months

Explanation

This child has latent tuberculosis infection, defined by evidence of infection without clinical or radiographic disease. Recommended regimens include 6 to 9 months of isoniazid, 4 months of rifampin, or short-course rifapentine-based regimens, all aimed at preventing progression to active disease.

Question 9Bacterial Infections and Mycobacterial Disease

A 7-year-old develops a papule on the hand that persists for 2 weeks, followed by tender regional lymphadenopathy after being scratched by a kitten. Which antibiotic is preferred if treatment is indicated?

  1. Cephalexin
  2. Azithromycin Correct answer.
  3. Trimethoprim-sulfamethoxazole
  4. Amoxicillin-clavulanate

Explanation

Cat-scratch disease is caused by Bartonella henselae, and azithromycin is the preferred agent when antibiotic therapy is warranted, such as for extensive or systemic disease. Many immunocompetent children with mild localized disease recover without antimicrobial therapy.

Question 10Bacterial Infections and Mycobacterial Disease

A fully immunized 4-year-old has fever, cough, and a right lower lobe infiltrate on radiograph. She is well-appearing, tolerates oral intake, and has normal oxygen saturation. Which outpatient antibiotic is most appropriate?

  1. Azithromycin
  2. High-dose amoxicillin Correct answer.
  3. Levofloxacin
  4. Intramuscular ceftriaxone

Explanation

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia in this age group, and high-dose amoxicillin provides reliable coverage. A macrolide is added or substituted when atypical pathogens are suspected, such as in older children with gradual onset and prominent cough.

Question 11Bacterial Infections and Mycobacterial Disease

A 5-year-old has fever, bloody diarrhea, and tenesmus, and stool culture grows Shigella sonnei. Which management is most appropriate?

  1. Loperamide alone
  2. Oral vancomycin
  3. Amoxicillin
  4. Azithromycin Correct answer.

Explanation

Antibiotic treatment shortens illness and reduces shedding in shigellosis, and azithromycin or ceftriaxone are preferred because resistance to ampicillin and trimethoprim-sulfamethoxazole is widespread. Antimotility agents are avoided because they can prolong fever and shedding.

Question 12Bacterial Infections and Mycobacterial Disease

An 18-month-old has 3 days of watery diarrhea and low-grade fever, and stool culture grows nontyphoidal Salmonella. He is well hydrated, immunocompetent, and has no signs of invasive disease. What is the most appropriate management?

  1. Oral azithromycin for 3 days
  2. Oral rehydration alone Correct answer.
  3. Oral ciprofloxacin for 5 days
  4. Intravenous ceftriaxone for 10 days

Explanation

Uncomplicated nontyphoidal Salmonella gastroenteritis in an immunocompetent child resolves with supportive care, and antibiotics do not meaningfully shorten illness. Antibiotics are reserved for young infants, immunocompromised children, and those with bacteremia or severe disease, because treatment can prolong carriage.

Question 13Bacterial Infections and Mycobacterial Disease

A newborn is born to a mother with untreated syphilis diagnosed late in pregnancy. The infant is asymptomatic. Which evaluation and treatment plan is appropriate?

  1. CSF studies and parenteral penicillin G for 10 days Correct answer.
  2. Oral amoxicillin for 14 days
  3. No evaluation or treatment because the infant is asymptomatic
  4. A single intramuscular dose of benzathine penicillin G

Explanation

Infants born to mothers with untreated or inadequately treated syphilis require full evaluation, including CSF analysis, blood counts, and long-bone radiographs, and are treated with intravenous aqueous crystalline penicillin G for 10 days. A single dose of benzathine penicillin is reserved for selected lower-risk infants after evaluation excludes neurosyphilis.

Question 14Bacterial Infections and Mycobacterial Disease

A 6-week-old presents with afebrile pneumonia, a staccato cough, tachypnea, and peripheral eosinophilia; the infant had conjunctivitis at 2 weeks of age. Which treatment is indicated?

  1. Intravenous vancomycin
  2. Intravenous ceftriaxone
  3. Oral azithromycin Correct answer.
  4. Oral amoxicillin

Explanation

The presentation suggests Chlamydia trachomatis pneumonia acquired perinatally, which is treated with a macrolide such as azithromycin or erythromycin. Tetracyclines are avoided in this age group because of effects on teeth and bone.

Question 15Bacterial Infections and Mycobacterial Disease

A 9-year-old has a 3-cm fluctuant, erythematous skin abscess with surrounding induration, is afebrile, and has no systemic signs. Which management is most appropriate?

  1. Intravenous vancomycin for 7 days
  2. Oral cephalexin alone for 10 days
  3. Topical mupirocin applied twice daily
  4. Incision and drainage alone Correct answer.

Explanation

Incision and drainage is the primary treatment for a purulent skin abscess in an otherwise healthy child, with antibiotics added when there is extensive cellulitis, systemic illness, or immune compromise. When empiric oral therapy is needed, it should cover methicillin-resistant Staphylococcus aureus.

Question 16Bacterial Infections and Mycobacterial Disease

A 12-year-old had an episode of acute rheumatic fever with arthritis and no evidence of carditis. Which secondary prophylaxis regimen is recommended?

  1. For 2 years after the most recent episode
  2. No prophylaxis is required
  3. For 5 years or until age 21 Correct answer.
  4. For 6 months after the most recent episode

Explanation

Penicillin prophylaxis prevents recurrent rheumatic fever, and the duration depends on whether carditis occurred. Without carditis, prophylaxis continues for 5 years after the last episode or until age 21, whereas carditis warrants a substantially longer course.

Question 17Bacterial Infections and Mycobacterial Disease

Which child most clearly warrants antibiotic prophylaxis before a dental procedure that involves manipulation of gingival tissue?

  1. A child with an innocent murmur and no structural disease
  2. A child with a ventricular septal defect repaired 4 years ago and no residual shunt
  3. A child with a prosthetic mitral valve Correct answer.
  4. A child with a history of Kawasaki disease and resolved coronary aneurysms

Explanation

Prophylaxis is recommended only for the highest-risk cardiac lesions, including prosthetic valves, previous infective endocarditis, unrepaired cyanotic congenital heart disease, and repaired lesions with residual defects. Completely repaired defects without residual shunt beyond 6 months, innocent murmurs, and resolved coronary findings do not require prophylaxis.

Question 18Bacterial Infections and Mycobacterial Disease

A 2-year-old refuses to bear weight on the left leg and has a low-grade fever. MRI shows septic arthritis of the hip, and blood cultures are pending. Which organism is a leading cause of osteoarticular infection in children of this age?

  1. Pseudomonas aeruginosa
  2. Kingella kingae Correct answer.
  3. Neisseria gonorrhoeae
  4. Streptococcus agalactiae

Explanation

Kingella kingae colonizes the oropharynx and is a leading cause of septic arthritis and osteomyelitis in children aged 6 months to 4 years, often following a recent upper respiratory infection. The organism is fastidious and may not grow in routine blood culture media.

Question 19Bacterial Infections and Mycobacterial Disease

A 10-year-old with culture-confirmed pulmonary tuberculosis has isolates resistant to both isoniazid and rifampin. Which statement about management is correct?

  1. At least four effective drugs selected by susceptibility testing Correct answer.
  2. Standard four-drug therapy continued for the usual 6 months
  3. Isoniazid at a higher dose combined with rifampin
  4. Ethambutol and pyrazinamide alone for 12 months

Explanation

Resistance to both isoniazid and rifampin defines multidrug-resistant tuberculosis, which requires a regimen of at least four effective agents chosen by drug-susceptibility testing, typically including a later-generation fluoroquinolone and a group A agent such as bedaquiline. Such regimens should be designed with expert consultation and continue for many months.

Question 20Bacterial Infections and Mycobacterial Disease

A 3-year-old has a 4-week history of a unilateral, nontender, violaceous submandibular lymph node that has not responded to oral antibiotics; there is no fever, and the chest radiograph is normal. Which diagnosis is most likely?

  1. Nontuberculous mycobacterial lymphadenitis Correct answer.
  2. Cat-scratch disease from a kitten scratch
  3. Tuberculous lymphadenitis with chest disease
  4. Recurrent streptococcal lymphadenitis

Explanation

Unilateral submandibular or cervical lymphadenitis that is violaceous, minimally tender, and unresponsive to standard antibiotics in a toddler is characteristic of nontuberculous mycobacterial infection, most often Mycobacterium avium complex. Excision is often both diagnostic and therapeutic.

Question 21Viral Infections

A 4-month-old infant has 3 days of rhinorrhea and cough followed by tachypnea, subcostal retractions, diffuse wheezing, and fine crackles. Which virus is the most likely cause?

  1. Adenovirus
  2. Human metapneumovirus
  3. Parainfluenza virus type 3
  4. Respiratory syncytial virus Correct answer.

Explanation

RSV is the single most common cause of bronchiolitis in children under 2 years and the leading reason for infant hospitalization with lower respiratory tract infection, peaking at 2 to 6 months of age. The typical pattern is an upper respiratory prodrome followed by wheeze, crackles, and increased work of breathing.

Question 22Viral Infections

A 6-year-old with varicella developed new vesicles for 4 days and now the earliest lesions have formed crusts. When may the child return to school?

  1. When all skin lesions have crusted over Correct answer.
  2. As soon as fever has been absent for 24 hours
  3. When the rash has completely faded
  4. After one dose of oral acyclovir

Explanation

Children with varicella are contagious from about 48 hours before rash onset until all lesions have crusted, usually 5 to 7 days after the rash appears. Exclusion and infection-control decisions are based on crusting of every lesion rather than on fever or antiviral treatment.

Question 23Viral Infections

A child has small white lesions on an erythematous base on the buccal mucosa, followed 2 days later by a maculopapular rash that begins on the face and spreads downward. Which infection is this?

  1. Scarlet fever
  2. Measles Correct answer.
  3. Parvovirus B19 infection
  4. Rubella

Explanation

Koplik spots are the pathognomonic enanthem of measles and appear 1 to 2 days before the rash, which then spreads cephalocaudally and often coalesces. The patient is highly infectious during this prodrome, which is why exposure history and immunization status matter so much.

Question 24Viral Infections

An 18-month-old has 3 days of fever to 40°C that resolves abruptly, followed within hours by a blanching maculopapular rash on the trunk. Which virus is responsible?

  1. HHV-6 Correct answer.
  2. Measles virus
  3. Rubella virus
  4. Parvovirus B19

Explanation

Roseola infantum is caused by human herpesvirus 6 (less often type 7) and is characterized by high fever for 3 to 5 days that defervesces just as a truncal rash appears. Febrile seizures may accompany the febrile phase, and the illness is generally self-limited.

Question 25Viral Infections

A 3-year-old has painful oral ulcers and a vesicular rash on the palms and soles. Which agent most commonly causes this illness?

  1. Enterovirus D68
  2. Varicella-zoster virus
  3. Herpes simplex virus type 1
  4. Coxsackievirus A16 Correct answer.

Explanation

Hand-foot-mouth disease is most often caused by coxsackievirus A16, with coxsackievirus A6 now also frequent in outbreaks. Lesions are distributed on the buccal mucosa, tongue, palms, and soles, and treatment is supportive because the illness is self-limited.

Question 26Viral Infections

A 2-year-old has a barking cough, hoarse voice, and inspiratory stridor that began after 2 days of coryza. Which virus most commonly causes this presentation?

  1. Adenovirus
  2. Rhinovirus
  3. Influenza A virus
  4. Parainfluenza 1 Correct answer.

Explanation

Croup (laryngotracheobronchitis) is most often caused by parainfluenza virus type 1, with types 2 and 3 also implicated. Subglottic edema produces the barking cough and stridor, and treatment rests on dexamethasone with nebulized epinephrine for moderate to severe disease.

Question 27Viral Infections

A 5-year-old with asthma presents 60 hours after the onset of fever and cough, and a rapid influenza A test is positive. What is the most appropriate management?

  1. Repeat the rapid influenza test before treating
  2. Start oseltamivir now Correct answer.
  3. Withhold antiviral therapy because the 48-hour window has passed
  4. Give amoxicillin and reassess in 48 hours

Explanation

Antiviral treatment is recommended as early as possible, but children who are hospitalized, severely ill, or at high risk of complications such as asthma should still be treated after 48 hours of symptoms. Antibiotics have no role in uncomplicated influenza, and repeat testing does not change the decision to treat.

Question 28Viral Infections

A 7-year-old with sickle cell anemia develops sudden pallor and fatigue, with hemoglobin falling from 8 to 4 g/dL and a low reticulocyte count. A sibling had a slapped-cheek rash 1 week earlier. Which virus explains this?

  1. Epstein-Barr virus
  2. Cytomegalovirus
  3. Human herpesvirus 8
  4. Parvovirus B19 Correct answer.

Explanation

Parvovirus B19 infects erythroid progenitor cells and causes transient arrest of red cell production. In children with shortened red cell survival such as sickle cell disease, this produces a transient aplastic crisis with profound anemia and reticulocytopenia, which may require transfusion.

Question 29Viral Infections

A 10-year-old has fever, exudative pharyngitis, and cervical lymphadenopathy; 3 days after starting amoxicillin he develops a diffuse maculopapular rash. What is the most likely explanation?

  1. EBV infection with an aminopenicillin rash Correct answer.
  2. IgE-mediated penicillin allergy requiring lifelong avoidance
  3. Drug-induced Stevens-Johnson syndrome
  4. Group A streptococcal scarlet fever

Explanation

Aminopenicillins given during acute Epstein-Barr virus infection frequently trigger a diffuse maculopapular rash that is not IgE-mediated and does not contraindicate future penicillin use. The underlying mononucleosis, with exudative pharyngitis and posterior cervical adenopathy, is the key clue.

Question 30Viral Infections

Which congenital infection is the leading non-genetic cause of sensorineural hearing loss in children?

  1. Congenital syphilis
  2. Toxoplasmosis
  3. Cytomegalovirus Correct answer.
  4. Congenital rubella

Explanation

Congenital cytomegalovirus is the most common congenital infection worldwide and the leading non-genetic cause of sensorineural hearing loss. Hearing loss may be present at birth or develop progressively over years, so serial audiologic testing is required even in asymptomatic infants.

Question 31Viral Infections

Which historical finding is a contraindication to receiving rotavirus vaccine?

  1. A prior febrile seizure
  2. Prematurity at 34 weeks' gestation
  3. Household contact with an immunocompromised person
  4. A previous episode of intussusception Correct answer.

Explanation

A prior episode of intussusception is a contraindication to rotavirus vaccination because the vaccine carries a small increased risk of intussusception, especially in the first week after the first dose. Severe combined immunodeficiency and history of severe allergic reaction to a vaccine component are other contraindications.

Question 32Viral Infections

A 10-day-old infant has vesicular scalp lesions, lethargy, and temperature instability, and CSF shows pleocytosis with elevated protein. What is the most appropriate immediate therapy?

  1. Ceftriaxone alone
  2. Oral acyclovir for 5 days
  3. IV acyclovir for 21 days Correct answer.
  4. Topical acyclovir with observation

Explanation

Neonatal herpes simplex virus disease with skin and central nervous system involvement requires high-dose intravenous acyclovir (60 mg/kg/day divided every 8 hours) for 21 days, with repeat CSF PCR to confirm clearance. Empiric acyclovir should be started promptly whenever neonatal HSV is suspected, because delayed therapy worsens outcomes.

Question 33Viral Infections

A term infant is born to a mother who is positive for both HBsAg and HBeAg. Besides hepatitis B vaccine, what should the infant receive, and when?

  1. Tenofovir prophylaxis starting at birth
  2. HBIG within 12 hours of birth Correct answer.
  3. No additional therapy; vaccine alone is sufficient
  4. HBIG at 2 months of age

Explanation

Infants born to HBsAg-positive mothers, especially those who are also HBeAg positive and highly infectious, should receive hepatitis B immune globulin and the first vaccine dose within 12 hours of birth. This combined passive-active immunoprophylaxis reduces perinatal transmission substantially, and completion of the vaccine series plus post-vaccination serologic testing follows.

Question 34Viral Infections

Which complication of mumps is most common in postpubertal males?

  1. Orchitis Correct answer.
  2. Aseptic meningitis
  3. Sensorineural deafness
  4. Pancreatitis

Explanation

Orchitis occurs in roughly 20 to 30 percent of postpubertal males with mumps, typically 1 to 2 weeks after parotitis, and may lead to testicular atrophy, though sterility is uncommon. Aseptic meningitis is common overall but is more often recognized in younger children.

Question 35Viral Infections

Several children develop fever, pharyngitis, and non-purulent conjunctivitis about a week after swimming together in a public pool. Which agent is most likely?

  1. Enterovirus 71
  2. Adenovirus Correct answer.
  3. Coxsackievirus B
  4. Epstein-Barr virus

Explanation

Adenovirus serotypes 3, 4, and 7 cause pharyngoconjunctival fever, which is notorious for outbreaks linked to inadequately chlorinated swimming pools because the virus resists standard chlorine levels. The triad of fever, pharyngitis, and non-purulent conjunctivitis is characteristic.

Question 36Viral Infections

A 5-year-old has 2 days of fever, headache, photophobia, and neck stiffness but is alert and interactive. CSF shows 200 white cells/µL with 80 percent lymphocytes, glucose 60 mg/dL with a serum glucose of 90 mg/dL, protein 45 mg/dL, and a negative Gram stain. What is the most likely diagnosis?

  1. Pneumococcal meningitis
  2. Partially treated bacterial meningitis
  3. Viral meningitis Correct answer.
  4. Tuberculous meningitis

Explanation

A lymphocytic pleocytosis with a normal CSF-to-serum glucose ratio, only mildly elevated protein, and a negative Gram stain in an alert child favors viral meningitis, most often caused by enteroviruses. Bacterial meningitis typically produces a neutrophilic pleocytosis with low glucose and high protein, and CSF should be reassessed if the child does not improve as expected.

Question 37Viral Infections

In an untreated HIV-infected pregnant woman, which statement best describes the timing of mother-to-child transmission?

  1. Transmission cannot occur before 20 weeks' gestation
  2. Most transmission occurs in the first trimester
  3. Most transmission occurs during labor and delivery Correct answer.
  4. Transmission occurs only through breast milk

Explanation

Without prophylaxis, the intrapartum period accounts for the largest share of transmission, roughly half to two-thirds in non-breastfeeding populations, with in utero transmission accounting for most of the remainder and breastfeeding adding additional risk. Maternal antiretroviral therapy, infant prophylaxis, and appropriate feeding decisions can reduce transmission to under 1 to 2 percent.

Question 38Viral Infections

A 9-year-old in a dengue-endemic area has 4 days of fever that suddenly resolves, followed by abdominal pain, persistent vomiting, and a rising hematocrit with a falling platelet count. What is the most appropriate interpretation?

  1. The findings indicate bacterial superinfection
  2. The illness is resolving and the child may be discharged
  3. The child has entered the critical plasma-leakage phase Correct answer.
  4. Platelet transfusion should be given immediately

Explanation

The critical phase of dengue begins around defervescence, usually day 3 to 7 of illness, when plasma leakage peaks over 24 to 48 hours and can produce shock. Warning signs such as abdominal pain, persistent vomiting, mucosal bleeding, lethargy, and a rising hematocrit with falling platelets mandate close monitoring and judicious isotonic fluid resuscitation.

Question 39Viral Infections

An 8-year-old is bitten on the hand by a stray dog of unknown vaccination status, and the skin is broken and bleeding. What is the appropriate post-exposure management?

  1. Wound washing, rabies vaccine, and rabies immunoglobulin Correct answer.
  2. Tetanus prophylaxis alone, since the wound is minor
  3. Observation of the animal for 10 days before starting vaccine
  4. Rabies vaccine alone, without immunoglobulin

Explanation

A transdermal bite that bleeds is a category III exposure, which requires immediate thorough wound washing with soap and water, the full rabies vaccine series, and rabies immunoglobulin infiltrated into and around the wound. Immunoglobulin provides passive antibody before the vaccine-induced response develops and is omitted only in previously vaccinated persons.

Question 40Viral Infections

A 10-year-old has 5 days of fever, conjunctivitis, rash, abdominal pain, and hypotension 4 weeks after a mild SARS-CoV-2 infection, with elevated CRP, troponin, and ferritin. Which diagnosis best fits?

  1. Acute viral hepatitis
  2. Streptococcal toxic shock syndrome with scarlet fever
  3. Kawasaki disease
  4. Multisystem inflammatory syndrome in children Correct answer.

Explanation

Multisystem inflammatory syndrome in children presents 2 to 6 weeks after SARS-CoV-2 infection with persistent fever plus multisystem involvement, commonly cardiac, gastrointestinal, mucocutaneous, and hematologic, with markedly elevated inflammatory markers. Kawasaki disease is the main differential but lacks the post-COVID timing and is typically seen in younger children; management includes IVIG with or without glucocorticoids and cardiology involvement.

Question 41Fungal and Parasitic Infections

A 9-month-old previously healthy infant has white plaques on the tongue and buccal mucosa that wipe off and leave a raw erythematous base. What is the most appropriate first-line therapy?

  1. Oral fluconazole
  2. Clotrimazole troches
  3. Nystatin suspension Correct answer.
  4. Oral griseofulvin

Explanation

Topical nystatin is first-line for uncomplicated oral candidiasis in an immunocompetent infant. Fluconazole is reserved for refractory, extensive, or immunocompromised cases. Troches must be dissolved slowly in the mouth and are unsuitable for an infant.

Question 42Fungal and Parasitic Infections

A 5-year-old has intense perianal itching that wakes him at night. What is the most sensitive diagnostic test for the suspected infection?

  1. Colonoscopy with biopsy
  2. Serum IgG testing
  3. Stool ova and parasite exam
  4. Cellophane tape test at dawn Correct answer.

Explanation

Enterobius vermicularis females deposit eggs on the perianal skin at night, so tape is applied first thing in the morning before bathing or defecation. Sensitivity improves with sampling on three consecutive days. Stool examination is unreliable because eggs are rarely shed into stool.

Question 43Fungal and Parasitic Infections

A 4-year-old in daycare has two weeks of foul-smelling watery diarrhea and poor weight gain. Stool testing identifies Giardia lamblia cysts. Which medication is first-line?

  1. Amoxicillin
  2. Nystatin
  3. Metronidazole Correct answer.
  4. Albendazole

Explanation

Metronidazole or tinidazole is first-line therapy for giardiasis in children. Albendazole is an anthelmintic with inconsistent activity against Giardia. Nystatin and amoxicillin have no meaningful activity against the organism.

Question 44Fungal and Parasitic Infections

A 6-year-old has a scaly patch of hair loss with broken hairs and black dots on the scalp; KOH preparation shows fungal elements. Topical therapy has failed. What is the most appropriate treatment?

  1. Topical terbinafine
  2. Topical clotrimazole
  3. Topical selenium sulfide
  4. Oral griseofulvin Correct answer.

Explanation

Dermatophytes causing tinea capitis invade the hair follicle and shaft, where topical agents cannot reach, so an oral agent such as griseofulvin or terbinafine is required for 6 to 8 weeks. Selenium sulfide and topical azoles may reduce shedding but do not cure the infection.

Question 45Fungal and Parasitic Infections

A 3-year-old returns from a Caribbean beach with an intensely itchy, serpiginous track on the sole of the foot. What is the treatment of choice?

  1. Albendazole Correct answer.
  2. Metronidazole
  3. Permethrin
  4. Griseofulvin

Explanation

Cutaneous larva migrans is caused by animal hookworm larvae that penetrate skin and migrate, producing a pruritic serpiginous track. Oral albendazole or ivermectin is the treatment of choice. The other listed agents target mites, dermatophytes, or anaerobic organisms and protozoa.

Question 46Fungal and Parasitic Infections

A 14-year-old has multiple hypopigmented, finely scaly macules on the trunk. KOH preparation shows short hyphae with round spores in a spaghetti-and-meatballs pattern. Which organism is responsible?

  1. Candida albicans
  2. Aspergillus fumigatus
  3. Malassezia furfur Correct answer.
  4. Trichophyton rubrum

Explanation

Malassezia furfur is a lipophilic yeast that is part of normal skin flora and overgrows to cause pityriasis versicolor. KOH shows short hyphae with round spores, the classic spaghetti-and-meatballs appearance. Topical selenium sulfide or an azole is effective.

Question 47Fungal and Parasitic Infections

An 8-month-old has bright red erythema in the diaper area with several small pustules scattered beyond the main rash and involvement of the skin folds. What is the most likely cause?

  1. Group A streptococcal infection
  2. Seborrheic dermatitis
  3. Candida albicans Correct answer.
  4. Tinea corporis

Explanation

Beefy red erythema with satellite pustules and involvement of skin folds is characteristic of Candida diaper dermatitis. KOH preparation shows budding yeasts and pseudohyphae. Topical nystatin or clotrimazole is usually sufficient.

Question 48Fungal and Parasitic Infections

A 7-year-old in the United States has tinea capitis with widespread scaling and broken hairs. Which organism is the most common cause in this setting?

  1. Microsporum canis
  2. Malassezia furfur
  3. Trichophyton rubrum
  4. T. tonsurans Correct answer.

Explanation

Trichophyton tonsurans is the most common cause of tinea capitis in the United States and spreads from person to person. Microsporum canis is acquired from pets and predominates in some other regions. Trichophyton rubrum typically causes tinea corporis, pedis, or cruris rather than tinea capitis.

Question 49Fungal and Parasitic Infections

A 10-year-old from the Ohio River valley has fever and cough two weeks after exploring a cave filled with bird droppings. Chest imaging shows hilar lymphadenopathy and a patchy infiltrate. Which organism is most likely?

  1. Coccidioides immitis
  2. Blastomyces dermatitidis
  3. Aspergillus fumigatus
  4. Histoplasma capsulatum Correct answer.

Explanation

Histoplasma capsulatum is endemic in the Ohio and Mississippi River valleys, and soil enriched by bird or bat droppings is a classic exposure. Children often have a self-limited flu-like illness with hilar adenopathy. Severe or disseminated disease requires amphotericin B.

Question 50Fungal and Parasitic Infections

A 6-year-old living in Arizona develops fever, cough, and painful red nodules on the shins, with a focal lung infiltrate on imaging. Which tissue finding is characteristic of the causative organism?

  1. Arthroconidia in tissue
  2. Spherules containing endospores Correct answer.
  3. Pseudohyphae with budding yeasts
  4. Broad-based budding yeasts

Explanation

In tissue, Coccidioides immitis forms spherules filled with endospores, which is the diagnostic finding. Arthroconidia are the infectious structures formed in soil, not the tissue form. Broad-based budding suggests Blastomyces, and pseudohyphae suggest Candida.