A 5-week-old girl is brought to the emergency department for increased fussiness. The infant had been feeding, voiding, and stooling normally since discharge from the nursery but has become increasingly irritable over the past 48 hours with decreased appetite and frequent crying. Temperature is 38.3 C (100.9 F). Mucous membranes are moist. Heart and lung examinations are unremarkable. The abdomen is soft and nondistended. A 5 × 6 cm area of redness and induration is noted along the left cheek and submandibular region; it has greatly expanded over the past hour. Leukocyte count is 22,000 cells/mm³. Blood, urine, and cerebrospinal fluid are collected for culture. The infant is admitted to the pediatrics unit, and broad-spectrum antibiotics are started. After 5 hours, the blood culture grows gram-positive cocci in pairs and chains. Which of the following is the most likely pathogen in this patient?

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Quizplus · Accepted Answer

11ec25c8_d6b7_5ac7_bc81_e39cb0821f3e_MD0003_00 This infant with gram-positive cocci in pairs and chains on blood culture most likely has infection due to Streptococcus agalactiae, also known as group B Streptococcus (GBS). GBS is the most common cause of early-onset neonatal sepsis in the first week of life (typically first 24 hours) due to vertical transmission during passage through a colonized vaginal canal. However, GBS can also cause late-onset infection in young infants age ≥7 days due to horizontal transmission of bacteria from colonized household members. Maternal intrapartum antibiotic prophylaxis does not reduce the incidence of late-onset disease. gram-positive cocci in pairs and chains Late-onset GBS most commonly presents at age 4-5 weeks with bacteremia, meningitis, or a focal infection (eg, cellulitis, osteomyelitis). This patient has cellulitis-adenitis, a well-described manifestation of GBS characterized by inflammation and induration of the face and/or submandibular area, often with associated adenopathy. Fever may be present, and patients typically have concomitant bacteremia. Workup includes blood, urine, and cerebrospinal fluid cultures as well as initiation of empiric antibiotics. Growth of S agalactiae on culture, which appears as gram-positive cocci arranged in pairs and short chains, is diagnostic. Definitive treatment is intravenous penicillin G. (Choices A and B) Clostridium perfringens and Corynebacterium species are gram-positive rods that cause gangrenous wound infections and respiratory symptoms (eg, diphtheria), respectively. (Choice C) Enterococcus faecalis is a gram-positive coccus that organizes into pairs and chains similar to GBS; however, E faecalis is a much less common cause of late-onset neonatal infection than GBS, and it typically causes urinary tract infections, not skin infections. (Choice D) Late-onset neonatal listeriosis can present with fever, poor feeding, and bacteremia, but cellulitis does not occur. In addition, Listeria monocytogenes is a gram-positive rod, not a coccus. (Choice E) Staphylococcus aureus infection should be suspected in a patient with cellulitis, but S aureus appears as gram-positive cocci in clusters, not in pairs and chains. Educational objective: Streptococcus agalactiae (group B Streptococcus) are gram-positive cocci in pairs and chains on culture. It can cause early-onset neonatal sepsis or late-onset disease in young infants. Late-onset infection most commonly presents at age 4-5 weeks with bacteremia, meningitis, and/or focal infection (eg, cellulitis-adenitis). References: Management of infants at risk for group B streptococcal disease. (http://www.ncbi.nlm.nih.gov/pubmed/31285392) Group B streptococcal cellulitis and necrotizing fasciitis in infants: a systematic review. (http://www.ncbi.nlm.nih.gov/pubmed/29424798)

A 5-Week-Old Girl Is Brought to the Emergency Department for Increased