2. The answer is c. A rash develops in approximately 80% to 90% of individuals with infectious mononucleosis caused by EBV or CMV who are inadvertently treated with ampicillin. The reason is unclear.

3. The answer is a. Parvovirus B19 is the cause of erythema infectiosum, also known as slapped cheek or fifth disease. An intense erythematous rash develops on the cheeks along with a systemic, lace-like eruption on the trunk and extremities (see Fig. 1.20). The eruption may be pruritic and is often evanescent.

4. The answer is d. Rubella, mostly an illness of adolescents and young adults in the postvaccine era, generally causes asymptomatic infection. The classic features, when present, include a discrete, often pinpoint rash that begins on the face and spreads to the trunk. Postauricular and postoccipital tender adenopathy is said to be most characteristic of rubella.

5. The answer is e. Classic roseola is characterized by 3 to 5 days of high fever, often associated with toxicity, followed by defervescence and the appearance of a maculopapular rash. Human herpes virus 6 is the etiologic agent of roseola; it is also a common cause of febrile illness without rash in infants and children.

6. The answer is b. Measles is characterized by a prodrome manifesting with fever, cough, coryza, conjunctivitis, and Koplik spots, the pathognomonic feature of measles. A rash, accompanied by high fever, follows the prodrome. The respiratory symptoms of measles, especially the cough, are striking. The rash typically begins on the neck, head, and face and spreads to the trunk and extremities. As the rash spreads, it becomes confluent.

Answer

The answer is e. M. pneumoniae is associated with many clinical manifestations. Atypical pneumonia in schoolaged children and adolescents is the most important of these. Indeed, M. pneumoniae is the most common cause of pneumonia in school-aged children. Pharyngitis as an isolated finding is rare but is common in conjunction with pneumonia. Approximately 2% to 4% of cases of croup are caused by this organism. M. pneumoniae and herpes simplex virus are the most common infectious agents of erythema multiforme/Stevens-Johnson syndrome. M. pneumoniae is also associated with bullous myringitis and otitis media, hemolytic anemia, and common gastrointestinal symptoms. Neurologic manifestations of infection with this organism include aseptic meningitis, encephalitis, Guillain-Barré syndrome, and transverse myelitis.

Answer

The answer is b. Pneumonia develops in approximately 10% to 20% of infants born to women with C. trachomatis infection. The illness usually presents in infants between 3 and 12 weeks of age, and 30% to 50% of them have a history of conjunctivitis. The clinical onset is insidious, with persistent cough, tachypnea, and rales as common clinical features. Fever is characteristically absent. Peripheral eosinophilia is common. Chest radiography reveals hyperinflation and interstitial infiltrates. Erythromycin for 14 days is the standard treatment for infants with Chlamydia pneumonia and conjunctivitis.

Chamydophila (formerly Chlamydia) pneumoniae does not cause pneumonia in young infants. The initial illness develops during the school age years and is associated with asymptomatic infection, pharyngitis, and atypical pneumonia. Pneumonia associated with group B streptococci most commonly accompanies early-onset disease and is uncommon in late-onset disease. S. pneumoniae and S. aureus cause in young infants severe, febrile pneumonia that is associated with an acute onset, toxicity, and focal infiltrates.

Answer

The answer is d. This infant has acute pyogenic cervical adenitis, which in most cases is caused by S. aureus, S. pyogenes, or anaerobic organisms. The adenitis is generally unilateral and occurs in children between the ages of 1 and 4 years. Infections with S. aureus can be difficult to distinguish from those with S. pyogenes, but in general, staphylococcal adenitis is more indolent although more likely to become suppurative (Fig. 51.1). Overall, 25% to 40% of infections with S. aureus become suppurative and require surgical drainage. Mycobacterial adenitis usually manifests as subacute or chronic lymphadenitis and is very rarely associated with fluctuance. B. henselae is the causative agent of cat scratch adenitis,
which characteristically has a subacute presentation. Group B streptococci can cause an adenitis-cellulitis syndrome, almost exclusively in neonates.

Answer

The answer is c. This child has subacute lymphadenopathy. Potential causes include:

Of the choices given, a complete blood cell count and chest radiography are reasonable given that malignancy and tuberculosis are included in the differential diagnosis. Incision and drainage of the lymph node are indicated if the node is fluctuant. Removal of the node is appropriate if the diagnosis of nontuberculous mycobacterial infection is thought likely and other causes have been excluded. A double-strength tuberculin skin test should never be utilized to assess previous exposure to tuberculosis or nontuberculous mycobacteria; a standard 5-TU skin test should be applied. Appropriate management before any invasive procedures are undertaken includes eliciting a detailed history, including tuberculosis and kitten exposures, and placing a 5-TU tuberculin test.

Further history reveals that the family has recently obtained a kitten with which the child has had close contact. The patient has no history of exposure to tuberculosis, and the result of a 5-TU tuberculin skin test is negative. On closer physical examination, you note a papule on the child’s face medial to the enlarged lymph node.

Answer

The answer is d. This child most likely has cat scratch adenitis. Ninety percent of patients report exposure to cats or kittens, and 75% have a history of a cat bite or scratch. B. henselae is the organism that causes cat scratch disease, and confirmation of infection can be documented with commercially available serologic testing. A cat scratch skin test, which utilizes antigen derived from human sera, is not recommended. Subacute tender regional lymphadenopathy, most commonly involving the axillae and face, is the most common clinical finding. A macule or papule at the inoculation site is found in 60% of cases (Fig. 51.2). Systemic symptoms, such as fever, are found in <35% of cases. Atypical clinical manifestations of cat scratch disease include:

The typical course of cat scratch adenitis is benign and self-limited. Therefore, antimicrobial therapy is not indicated in most cases. Antimicrobial therapy is commonly used for severe atypical disease, such as encephalitis, although no controlled trials have assessed the efficacy of such therapy.

Answer

The answer is c. The history and clinical features are most consistent with primary spontaneous peritonitis. This entity is extremely rare in healthy children; it occurs in children with underlying ascites resulting from nephrotic syndrome, liver disease, or rheumatic disorders. Children receiving corticosteroid therapy, which may mask the clinical features of peritonitis, are at highest risk. The organisms most commonly reach the peritoneum by hematogenous spread. Paracentesis is the procedure of choice to confirm the diagnosis; a large number of polymorphonuclear cells (>250/μL), a protein level >1 g/dL, a glucose level <50 mg/dL, and the presence of only gram-positive organisms with Gram staining are features that favor a diagnosis of primary peritonitis.

Answer

The answer is d. E. coli and S. pneumoniae are the most common causes of primary peritonitis. Other, less common organisms include group A streptococci and Klebsiella pneumoniae. Anaerobes are not commonly isolated from the peritoneal fluid of patients with primary peritonitis, as they are present in secondary peritonitis. Therefore, antimicrobial therapy should include coverage against pneumococci and other streptococci in addition to coverage against gram-negative aerobes. Because a large percentage of E. coli organisms produce β-lactamases, ampicillin monotherapy is not adequate for initial therapy. The aminoglycosides provide good coverage against gram-negative aerobes but not against
pneumococci. Metronidazole is not required for initial therapy because anaerobes are not common pathogens in primary peritonitis. Nafcillin and clindamycin have no activity against gram-negative organisms. Ceftriaxone provides excellent activity against gram-negative aerobes and S. pneumoniae and should be sufficient even for penicillin-resistant strains of pneumococci.

Answer

The answer is a. Appropriate antimicrobial therapy for AOM must take into account the pathogens involved and their resistance patterns. The three most common causes of AOM are S. pneumoniae, nontypable H. influenzae, and M. catarrhalis. H. influenzae and M. catarrhalis induce β-lactamases as their mechanism of resistance, which cannot be overcome by increasing the dosage of a β-lactam antibiotic agent. In contrast, resistance by the pneumococcus is mediated by altered penicillin-binding proteins, which is a stepwise process that can be overcome by increasing the dosage of β-lactams. On the basis of in vitro activity and achievable concentrations in the middle ear, amoxicillin is the most active of the oral β-lactams for the treatment of nonsusceptible strains of S. pneumoniae. The addition of clavulanate to amoxicillin adds a β-lactamase inhibitor to counter the effects of β-lactamases produced by H. influenzae and M. catarrhalis, but provides no added activity against S. pneumoniae. Although clindamycin has activity against S. pneumoniae and has been utilized to treat resistant pneumococcal infections, it does not have activity against H. influenzae and M. catarrhalis, and is therefore not recommended as initial empiric therapy. The macrolide antibiotics should not be used as first-line therapy for AOM, given the increasing rates of resistance against these agents, which is as high as 30% for strains of S. pneumoniae. These agents should be utilized as alternatives in patients who have severe allergies to β-lactam agents.

Answer

The answer is c. B. pertussis infection in young infants is associated with many of the features described in the case study. In neonates with pertussis, the classic paroxysmal cough may not be apparent, and the catarrhal stage is frequently absent or brief. These infants often present with feeding difficulties, recurrent episodes of gagging, apnea, bradycardia, and cyanosis. Apnea can follow episodes of coughing and gagging or can occur spontaneously during the course of the illness. Posttussive emesis is very common at all ages. Laboratory features of pertussis include a leukocytosis with absolute lymphocytosis, the degree of which parallels the severity of the illness. The lymphocytosis consists of small T and B lymphocytes (Fig. 51.5) rather than the atypical-appearing lymphocytes of infectious mononucleosis. Thrombocytosis is common in children with pertussis infection. The differential diagnosis of pertussis includes:

Answer

The answer is b. Heterophil antibodies are produced in EBV infection but not infectious mononucleosis syndromes with other causes, such as CMV or Toxoplasma, and in human immunodeficiency virus infection. The rapid spot tests (monospot slide tests) are highly sensitive and specific for EBV infection in older children. However, the antibodies may be absent in young children with EBV infection, and the diagnosis may require specific EBV serology. Absolute lymphocytosis with atypical lymphocytosis is not specific for EBV infection; it can be seen in infectious mononucleosis with other causes. Children <2 years are most commonly asymptomatic. Children, in comparison with adolescents, more frequently have nonspecific symptoms, such as fever, rash, abdominal pain, and upper respiratory symptoms. Older children and adolescents have more classic, mononucleosis-like symptoms. Antibodies to the nuclear antigen of EBV are produced 4 weeks after acute infection, are indicative of past infection, and persist for life. Immunoglobulin M (IgM) antibodies to the viral capsid antigen are produced early in the course of infection, are indicative of acute infection, and last for weeks to months. IgG antibodies to the viral capsid antigen are produced at the time of acute infection and last for life. Antibodies to the early antigen are produced acutely, disappear, and can reappear spontaneously.

Answer

The answer is b. Facial nerve palsies and encephalitis are the most common neurologic complications of infectious mononucleosis. Others include Guillain-Barré syndrome and transverse myelitis. Mild thrombocytopenia occurs in up to 50% of patients with infectious mononucleosis. Mild autoimmune hemolytic anemia and granulocytopenia can also occur. Although mild subclinical hepatitis is common in infectious mononucleosis, severe hepatitis and liver failure are extremely rare and are seen in patients with X-linked lymphoproliferative disorder. Corticosteroid therapy for patients with infectious mononucleosis is indicated only in cases of severe airway obstruction secondary to tonsillar hypertrophy.

Answer

The answer is a. This infant has staphylococcal scalded skin syndrome (SSSS), a toxin-mediated process caused by circulating exfoliative toxins of S. aureus. The organism is very rarely recovered from the blood or bullous lesions because it is the toxin elaborated by the organism that is responsible for the epidermolysis. The organism most commonly is found in the nasopharynx, conjunctivae, umbilicus, or at the site of previous trauma or surgery, such as circumcision. SSSS is most common in infants and children <5 years. Malaise, fever, and tender skin are the first signs of infection, followed by diffuse erythema, a wrinkled appearance of the skin, circumoral erythema, and flaccid blisters. Facial edema and perioral crusting are common. Desquamation of the skin occurs 2 to 5 days after the onset of the erythema, representing cleavage of the stratum granulosum layer of the epidermis. The Nikolsky sign is separation of the epidermis by gentle shear force. The absence of a strawberry tongue in SSSS can help in differentiating this entity from systemic
skin infections caused by group A streptococci. Infants with SSSS generally appear well except for irritability likely caused by skin tenderness. Treatment with systemic antistaphylococcal antibiotics is indicated.