A 14-day-old female neonate is brought to the emergency department by her parents due to f… — USMLE Step 2 CK

A $14$ -day-old female neonate is brought to the emergency department by her parents due to fever and decreased oral intake for the past $24$ hours. The patient was born at $39$ weeks of gestation via vaginal delivery complicated by fetal heart rate decelerations, which required the application of a fetal scalp electrode. The mother is a $22$ -year-old primigravida who received limited prenatal care. At presentation, the neonate's temperature is $38.4^\circ\text{C}$ ( $101.1^\circ\text{F}$ ), heart rate is $172/\text{min}$ , and respiratory rate is $48/\text{min}$ . Physical examination reveals a lethargic but arousable infant. The anterior fontanelle is full. Examination of the scalp reveals a $2\text{ cm}$ cluster of erythematous vesicles with clear fluid overlying the vertex. The remainder of the physical examination is unremarkable.

Laboratory evaluation reveals:

Test	Result	Reference Range
Hemoglobin	$15.2\text{ g/dL}$	$13.5-19.5\text{ g/dL}$
Leukocytes	$13,500/\mu\text{L}$	$9,000-30,000/\mu\text{L}$
Platelets	$105,000/\mu\text{L}$	$150,000-400,000/\mu\text{L}$

A lumbar puncture is performed, and cerebrospinal fluid (CSF) analysis reveals:

Test	Result	Reference Range
Leukocytes	$85/\mu\text{L}$ ( $80\%$ lymphocytes)	$0-28/\mu\text{L}$
Erythrocytes	$15/\mu\text{L}$	$0-10/\mu\text{L}$
Glucose	$45\text{ mg/dL}$	$34-119\text{ mg/dL}$
Protein	$110\text{ mg/dL}$	$20-170\text{ mg/dL}$

Which of the following is the most appropriate next step in management?

A
Reassurance and close outpatient follow-up in 24 hours
B
Intravenous ampicillin and gentamicin
C
Intravenous ceftriaxone, vancomycin, and acyclovir
D
Intravenous acyclovir alone
Intravenous ampicillin, cefotaxime, and acyclovirAnswer

Answer

The most appropriate next step is the administration of intravenous ampicillin, cefotaxime, and acyclovir.

This neonate presents with fever, a full fontanelle, and cerebrospinal fluid (CSF) pleocytosis, establishing a diagnosis of meningitis. Furthermore, the grouped vesicles on the scalp—particularly at the site of a fetal scalp electrode, which breaks the skin barrier and facilitates viral inoculation—strongly suggest neonatal herpes simplex virus (HSV) infection. Neonatal HSV can manifest as localized skin, eye, and mouth (SEM) disease, CNS disease, or disseminated disease. When a neonate presents with signs of meningitis and a vesicular rash, standard management requires immediate empiric coverage for both the most common bacterial pathogens (*Streptococcus agalactiae*, *Escherichia coli*, *Listeria monocytogenes*) and HSV. Ampicillin and cefotaxime provide excellent bacterial coverage and CNS penetration. Importantly, cefotaxime is used instead of ceftriaxone, as ceftriaxone is contraindicated in neonates due to its propensity to displace bilirubin from albumin, increasing the risk of kernicterus. Acyclovir is added to provide life-saving coverage for HSV.

Step-by-Step Solution

Analyze the patient's clinical presentation.

The

14

-day-old neonate has a fever, lethargy, a full fontanelle, and cerebrospinal fluid pleocytosis, which confirms the presence of meningitis.

Identifying meningitis dictates the need for immediate, broad-spectrum empiric central nervous system (CNS) coverage.

Evaluate the specific rash and maternal history.

The presence of grouped vesicles on the scalp at the site of a fetal scalp electrode in a mother with limited prenatal care points toward neonatal Herpes Simplex Virus (HSV) infection.

Scalp electrodes can inoculate the virus into the infant's skin during delivery, making this a classic presentation of neonatal HSV with CNS involvement.

Determine the necessary pharmacological coverage.

The patient requires antiviral coverage for HSV (acyclovir) AND empiric bacterial coverage for common neonatal pathogens such as Group B Streptococcus, E. coli, and Listeria monocytogenes.

Bacterial meningitis cannot be definitively ruled out until cultures result, necessitating concurrent antibacterial and antiviral therapy.

Select the appropriate specific agents.

Ampicillin covers Listeria, and cefotaxime covers Gram-negative organisms like E. coli. Acyclovir covers HSV.

Ceftriaxone must be avoided in neonates due to the risk of bilirubin displacement and kernicterus, making cefotaxime the preferred third-generation cephalosporin.

Key Concept

Empiric management of neonatal meningitis with suspected HSV

Estimated Time:1m 30s

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