Definition. Infection with MRSA (clustered Gram-positive cocci) causes a variety of localized and invasive suppurative infections and toxin-mediated syndromes like toxic shock syndrome and scalded skin syndrome. MRSA infections used to be limited to health-care facilities (HC-MRSA) and were strictly nosocomial; however, a significant increase in community-acquired MRSA (CA-MRSA) was noted recently.
Incidence. The methicillin-sensitive Staphylococcus aureus normally colonizes the nose, umbilicus, and the groin area by 1 week of age with a colonization rate of 20–90%. Maternal anogenital colonization with MRSA is usually ~3.5%, with little or no risk for early-onset disease in the newborn. There are several documented outbreaks of invasive CA-MRSA that developed in healthy newborn infants discharged from normal newborn nurseries as well as neonatal intensive care units (NICUs). The majority of MRSA infections in the NICU are of late onset. The incidence of disease in the newborn is not known because most literature describes outbreaks of MRSA infection. A recent study showed NICU colonization rate of 10.4%, with a mean time to acquire MRSA of 17 days.
Pathophysiology. If the newborn infant is exposed to MRSA, whether from the community or the hospital, then he or she will colonize with more virulent strains that are more likely to cause invasive disease. MRSA has specific virulence factors that make it more invasive than methicillin-sensitive Staphylococcus aureus. These include staphylococcal chromosome cassette (SCC) mecA, Panton-Valentine leukocidin (PVL), and staphylococcal enterotoxins. The SCC mecA has the genes that encode antibiotic resistance. PVL genes lead to the production of cytotoxins that form pores in the cellular membrane and cause tissue necrosis and cell lysis.
Risk factors for MRSA infection outbreaks include overcrowding, inconsistent handwashing, invasive procedures (eg, central lines, endotracheal intubations, nasogastric tubes), and prolonged hospital stay.
Clinical presentations. Invasive MRSA disease is likely to be preceded by colonization (skin, umbilicus, and nasopharynx). The source of the bacteria could be a health-care worker, another patient, equipment, or a family member.
Bloodstream infections are usually catheter related. Common clinical signs are nonspecific and include apnea or hypoxia, fever, elevated C-reactive protein, and leukocytosis.
Septic arthritis and osteomyelitis.S. aureus is the primary cause of septic arthritis and osteomyelitis in the neonate. Symptoms are nonspecific, such as poor feeding or increased irritability. Signs include soft tissue swelling and erythema.
Endocarditis. Neonates with congenital heart disease and percutaneous central catheters are at a higher risk for endocarditis.
Skin and soft tissue infections.S. aureus is the most common pathogen causing pustulosis and cellulitis in the neonate. MRSA has virulence factors that contribute to the pathogen's ability to damage the neonatal skin that is already compromised.
Surgical site infections.
Diagnosis. The gold standard for diagnosing a bloodstream infection is a positive blood culture. Diagnosing arthritis and osteomyelitis can be challenging. In addition to a blood culture, the work-up should include a joint aspirate, bone culture (if surgical debridement is done), radiography, and possibly magnetic resonance imaging. Echocardiography (to diagnose endocarditis) is strongly recommended in infants with more than one ...
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