Elsevier

Clinics in Perinatology

Volume 37, Issue 3, September 2010, Pages 535-546
Clinics in Perinatology

Staphylococcus aureus: A Continuously Evolving and Formidable Pathogen in the Neonatal Intensive Care Unit

https://doi.org/10.1016/j.clp.2010.05.002Get rights and content

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Epidemiology

The National Institute of Child Health and Human Development (NICHD) Neonatal Research Network maintains a prospective registry of early- and late-onset infections among very low-birth-weight (VLBW; ≤1500 g) infants. S aureus is a rare cause of early-onset sepsis in VLBW infants. In an evaluation of 5447 VLBW infants between 1998 and 2000, 84 patients had early-onset septicemia of which only 1 patient was infected with S aureus,21 and this low incidence was confirmed in a more recent

Resistance and virulence factors

The staphylococcal chromosome cassette (SCC) mecA has the genes responsible for antibiotic resistance, including mecA, which encodes for the penicillin-binding protein 2A (PBP 2A). PBP 2A has much lower affinity for β-lactam antibiotics when compared with natural binding proteins, thus interrupting the mechanism by which the β-lactam antibiotics block cell wall synthesis.32

Different SCC mec types are associated with the previous decade's classic HA-MRSA (SCC mecA I–III) and the current epidemic

A blurred border between MRSA and MSSA

Following the rapid increase in the number of CA-MRSA cases almost a decade ago, CA-MSSA is increasingly associated with severe and invasive disease. In fact, invasive disease is more often associated with CA-MSSA than with CA-MRSA isolates.43 The USA300 clone (with its characteristic pathogenicity island) is not only increasing as MRSA isolates but also as CA-MSSA isolates. In a study from Houston, 25% of MSSA isolates were USA300 clones and these isolates were associated with more severe

Clinical manifestations

SSTIs, including osteomyelitis, surgical wound infections and cellulitis, are common manifestations of S aureus infections in neonates.46, 47, 48 Compared with classic MSSA and HA-MRSA, CA-MRSA is highly associated with skin and skin structure infection and abscesses in adults and children.49 There may also be a difference in the invasiveness of S aureus infections, with MSSA predominating among children with invasive infections and CA-MRSA predominating among children with SSTIs.42, 50

In this

Well-newborn nursery

Although the NICU population is at great risk of developing nosocomial infections,33S aureus is not relegated solely to hospital units with critically ill, immunocompromised patients. In fact, S aureus is a serious threat in the well-newborn nursery. Skin infections with CA-MRSA (USA300) among otherwise healthy full-term newborns occurring within 30 days of delivery (typically during the second week of life) have been reported in Illinois,52 California,52 and Texas.28 All neonates had an

Treatment

Vancomycin remains the first-line therapy for MRSA infections, and many NICUs with endemic MRSA use vancomycin as the empiric therapy for late-onset sepsis while awaiting culture results. However, the early development of vancomycin-insensitive S aureus has been observed in several studies reporting an increase in the minimum inhibitory concentrations (MICs).55, 56 Simply looking at categorical results of resistance or susceptibility, this relative decline in susceptibility, the so-called MIC

Prevention

Risk factors for CA-MRSA versus HA-MRSA colonization in neonates hospitalized in NICUs include birth by vaginal delivery, endotracheal intubation, maternal substance abuse during pregnancy, and a higher gestational age and birth weight.65

It is difficult to determine the most effective measures for containment of MRSA, because during an outbreak, many measures are instituted concurrently. In 2006, a consensus statement was released from the Chicago Department of Public Health on management of

Summary and future directions

S aureus is a particularly formidable pathogen in the neonate. The natural history of present MSSA/MRSA community-based epidemics suggests that control will be challenging and eradication impossible. Optimal management and prevention of S aureus infections in nurseries require well-designed, scientifically rigorous, prospective intervention, and outcome studies. These requirements are the opportunities to advance effective strategies and to direct research and development of novel approaches

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      However, most of the USA300 strains recovered in Italy so far belong to an ACME-negative variant, and are probably less likely to cause outbreaks.8 CA-MRSA is a dangerous pathogen for neonates: several outbreaks of CA-MRSA have been reported in the USA and Europe both in NICUs and in well-newborn nurseries.3,5–7,12,13 The spread of CA-MRSA strains can be facilitated by the overcrowding of the newborn nursery settings and there can be transmission from neonate to neonate by staff members.12,13

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