Pediatric Examination and Board Review (171 page)

3.
(E)
PCR has become the diagnostic test of choice. The enzyme immunoassay of nasal specimens also has advantages including ease of performance, low cost compared with culture, technical simplicity, and short time to a result compared with immunofluorescence assays. The nasal wash is the preferred specimen for diagnostic testing with a higher yield than specimens obtained by swabs.

4.
(E)
Extended-spectrum beta-lactamase producing
E coli
were once somewhat difficult to detect in the laboratory, but with modern technique, can now be detected with relative ease. This is related to the difficulty in identifying those organisms that produce these beta-lactamases. Currently, isolates of these species that have MICs of 2 μg/mL or more to cefpodoxime, ceftazidime, cefotaxime, or ceftriaxone should be considered possible ESBL producers.

5.
(B)
For treatment of nonmeningeal infections caused by penicillin nonsusceptible
S pneumoniae
isolates, the organism is considered susceptible to ceftriaxone if the MIC is 1.0 μg/mL or less. For treatment of meningeal infections, the breakpoint for ceftriaxone susceptible is 0.5 μg/mL or less (
Table 97-1
).

TABLE 97-1
Interpretation of Susceptibility Testing for Streptococcus Pneumoniae to Antimicrobial Agents

Abbreviation: MIC, minimum inhibitory concentration.

6.
(D)
Anemia is not an adverse reaction associated with vancomycin. Dose-related anemia with reticulocytopenia is an adverse reaction reported commonly with chloramphenicol. This red-man syndrome results in flushing of the upper part of the body during rapid IV infusion of vancomycin.

7.
(C)
Linezolid does not require measurement of serum concentrations during therapy. Nonrenal pathways account for more than 80% of total body clearance, and only minor age-related changes in clearance have been observed in children of varying ages.

8.
(A)
Beta-lactamase production is the most frequent mechanism of ampicillin resistance with
Haemophilus
species and can be rapidly detected in the laboratory. The same test can be used to detect penicillin resistance in
Neisseria gonorrhoeae
.
H influenzae
strains are not susceptible to oxacillin. Kirby-Bauer susceptibility testing takes several days.

9.
(E)
Isolation of
Leptospira
from blood or CSF specimen can be very difficult, requiring special media, techniques, and long incubation times. Serology is the method of choice for diagnosis, with the macroscopic slide agglutination test the most useful serologic test for screening. Antibodies usually develop during the second week of illness.

10.
(C)
Localized erythema migrans usually occurs 1-2 weeks after a tick bite so antibodies against
Borrelia burgdorferi
will not be detectable. IgM antibodies appear 3-4 weeks after infection begins and peak by 6-8 weeks. Specific IgG antibodies usually appear 4-8 weeks after onset of infection and peak 3-6 months later. The EIA test should be corroborated with the Western immunoblot test. The practice of ordering serologic tests for patients with nonspecific symptoms such as chronic fatigue or arthralgia is not recommended.

11.
(B)
The newborn infant most likely has toxoplasmosis. Serologic tests are the primary approach to the diagnosis of congenital toxoplasmosis. It is important to send blood specimens to a reference laboratory with expertise in performing toxoplasma neonatal serologic assays with interpretive expertise. HSV and CMV are best diagnosed by culture. The diagnosis of lymphocytic choriomeningitis virus is best made by serology, but virus isolation is possible.

12.
(A)
The clinical picture is highly suggestive. The nontreponemal tests for syphilis (RPR, Venereal Disease Laboratory Test [VDRL]) are sensitive but can produce false-positive results. The treponemal tests (TP-PA, FTA-ABS) are more specific, and a positive TP-PA would confirm the diagnosis of congenital syphilis. Antibody tests including TP-PA and FTA-ABS should be interpreted with caution because the presence of an antibody in a neonate may represent passive transfer.

13.
(B)
This child most likely has acute EBV infection. Children younger than 5 years with acute EBV infection often have results for heterophil antibody tests that are negative. With acute EBV infection VCA-IgM and VCA-IgG will be positive and serum antibody to the EBV nuclear antigen (EBNA) will be negative. IgM for hepatitis A would be diagnostic but that disease more often presents with clinically apparent jaundice. HHV-6 infection is usually associated with a rash. CMV can cause a “mono” syndrome but a urine culture is not diagnostic.

14.
(A)
Diagnostic techniques such as the HSV DFA of skin lesions have the advantage of a rapid turnaround time. This technique is as specific but slightly less sensitive than viral culture. For the diagnosis of neonatal HSV infection, specimens for culture should also be obtained from skin vesicles, mouth or nasopharynx, eyes, urine, blood, stool or rectum, and cerebrospinal fluid (CSF). The Tzanck test (examination for multinucleated giant cells and eosinophilic intranuclear inclusions) has lower sensitivity. The CSF should be tested for the presence of HSV DNA by PCR.

15.
(B)
Of the viruses listed, only measles can be diagnosed by culture, although the simplest method of establishing the diagnosis of measles is by testing for the presence of measles immunoglobulin IgM antibody on a serum specimen obtained during acute illness. Calicivirus and hepatitis E can be diagnosed with a reverse-transcriptase-polymerase chain reaction (RT-PCR) assay for detection of viral RNA in stool as well as by serology. Parvovirus B19 can be diagnosed by serology or PCR assay.

16.
(E)
Vaccination with BCG vaccine can acutely result in a positive TST. However, the interpretation of TST results among BCG recipients should be the same for people who have not received BCG vaccine. The 16 mm induration, abnormal chest radiograph, and contact with an adult who has a risk factor (HIV) for tuberculosis make it likely that current tuberculosis infection is the cause of the positive TST. The presence of a BCG scar implies vaccine receipt but should not be used to aid in TST interpretation.

17.
(C)
A negative Mantoux test does not exclude the diagnosis of tuberculosis disease such as pulmonary tuberculosis or latent tuberculosis infection (LTBI). Approximately 10% of immunocompetent children with culture-proven tuberculosis do not react initially to a Mantoux test. Young age (<1 year), malnutrition, and receipt of measles vaccine can increase the likelihood for a negative Mantoux test. The effect of measles vaccine on tuberculin reactivity is temporary and should not last for more than 4-6 weeks after vaccination.

18.
(A)
All of the factors noted except bilateral location of lymphadenopathy are more likely associated with nontuberculous mycobacterial species. Adenitis due to NTM is usually unilateral and most commonly involves a submandibular node or an anterior superior cervical node.

S
UGGESTED
R
EADING

Christenson JC, Korgenski EK. Laboratory diagnosis of infection because of bacteria, fungi, parasites and rickettsiae. In: Long SS, Pickering LK, Prober CG, eds.
Principles and Practices of Infectious Diseases.
3rd ed. Philadelphia, PA: Churchill Livingstone; 2008: 1341.

Pickering LK, Baker CJ, Kimberlin DW, Long SS.
Red Book 2009 Report of the Committee on Infectious Diseases.
28th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2009.

CASE 98: A 9-MONTH-OLD WITH FEVER AND CEREBROSPINAL FLUID PLEOCYTOSIS

A 9-month-old male infant was seen by his pediatrician 7 days before admission to the hospital with fever to 101.3°F (38.5°C) and runny nose. He was diagnosed with an uncomplicated viral upper respiratory tract infection and sent home. Two days later the infant was brought to the children’s hospital emergency department because of persistent fever. At that time he was diagnosed with bilateral otitis media, prescribed amoxicillin, and sent home. No laboratory workup was done at the time. Amoxicillin was given as prescribed for the next 5 days, but the patient continued to be febrile. His appetite and activity level decreased. So the parents brought him back to the emergency department the next day.

On physical examination the infant was noted to be irritable. Both tympanic membranes were dull gray with decreased mobility. Nuchal rigidity was present. Examination of the lungs, heart, and abdomen were normal. A spinal tap was performed with these results: WBC 1200/mm
³
(S-65, L-30, M-5), RBC 10/mm
³
, glucose 10 mg/dL, and protein 100 mg/dL.

SELECT THE ONE BEST ANSWER

1.
The Gram stain of the CSF shows gram-positive diplococci, and the culture of the CSF grows
S pneumoniae
(
Figure 98-1
). The MIC of penicillin is 0.1 μg/mL and of cefotaxime is 0.25 μg/mL. The appropriate antibiotic therapy for treatment of this infection is

(A) ceftriaxone

(B) chloramphenicol

(C) penicillin G

(D) rifampin

(E) vancomycin

2.
You are asked about the indications for different formulations of penicillin (pen) including Pen V, procaine pen G, and benzathine pen G. Procaine pen G is appropriate for treatment of which of the following infections?

(A) congenital syphilis in a neonate

(B) group A streptococcal pharyngitis in a schoolage child

(C) actinomycosis in an adolescent