SEPTEMBER, 2021 Question: A three-week-old female neonate with a fever is brought to the emergency department. Earlier in the day, she was noted to be fussy and was not feeding well. One hour prior to presentation, she had a rectal temperature of 38.1ºC. She was full-term at birth and has no medical conditions. She has a temperature of 38ºC, blood pressure of 87/55 mm Hg, heart rate of 140 beats/min, and respiratory rate of 40 breaths/min. She cries during physical examination but is consolable. A fine maculopapular rash is seen over her thorax. The remainder of the physical examination findings is normal. She undergoes an evaluation for a serious bacterial infection and is started on ampicillin and gentamicin. Her urine is negative for blood, protein, nitrite, and leukocyte esterase. Final results of a urine culture are pending. Laboratory data are shown: Laboratory Test
Result
Blood White blood cell count
4,500/µ (4.5 x 10º/ )
Hemoglobin
9.8 g/d (98 g/ )
Platelet count
175 x 103/µ (175 X 10º/ )
Culture
Gram-positive cocci in clusters; negative for
Staphylococcus aureus by molecular testing
Cerebrospinal Fluid White blood cell count
3/µ
Red blood cell count
440/µ
Glucose
57 mg/d (3.2 mmol/ )
Protein
80 mg/d
Culture
Gram stain, no organisms seen; culture, pending
Of the following, the BEST next step in management is A. No further testing, add vancomycin B. No further testing, no medication change C. Repeat blood culture, add vancomycin D. Repeat blood culture, no medication change
Answer: B The best management of the neonate in this vignette is no further testing and no medication change. The blood culture drawn for evaluation of serious bacterial infection is positive for gram-positive cocci in clusters, and molecular testing has excluded Staphylococcus aureus. Therefore, one can infer that the organism is coagulase negative staphylococci (CoNS). The neonate was born at term and has no underlying medical condition or indwelling device that would predispose her to an invasive infection with CoNS. The most likely explanation for the positive blood culture is bacterial contamination of the blood culture from a common skin organism. Risk factors for CoNS infection include prematurity, especially in infants who weigh less than 1,500 g, and foreign devices or material. Indwelling devices at risk for colonization with CoNS include central venous catheters, ventriculoperitoneal shunts, and peritoneal catheters. Other foreign material at risk for colonization includes orthopedic hardware, baclofen pumps, prosthetic joints, pacemakers, and prosthetic valves. The ability of CoNS to proliferate in foreign material is mediated in part by the organism’s ability to create biofilm, which is an aggregate of bacteria encased in extracellular material. Biofilm is relatively impermeable to host defenses and antibiotics. Repeating a blood culture is not necessary for the neonate in this vignette because there is enough information provided to assume that the result represents contamination, rather than actual bacteremia. It is not necessary to add vancomycin to cover the organism identified in culture because it represents a blood culture contaminant.