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MSSA-associated infections, deaths occur more often than MRSA in NICU
Methicillin-susceptible Staphylococcus aureus caused more infections and deaths in a neonatal intensive care unit than MRSA, while both strains were found to have similar mortality rates after infection in a recent study.
“S. aureus infections are associated with increased mortality and morbidity and longer hospital stays, but data on the burden of S. aureus disease in hospitalized infants are limited.” Daniel K. Benjamin Jr., MD, PhD, faculty associate director of the Duke Clinical Research Institute at Duke University School of Medicine, and colleagues wrote. “Our findings confirm results of earlier studies demonstrating that MSSA infections are more common than MRSA infections.”
Daniel K. Benjamin Jr.
Benjamin and colleagues conducted a retrospective study of 3,888 neonates with invasive S. aureus infections discharged from 348 NICUs from 1997 through 2012. Study findings revealed that of all patients discharged from NICUs (n = 887,910), 0.4% were diagnosed with an invasive S. aureus infection. Of the 3,978 S. aureus infections, MSSA accounted for 72.1% of them. The proportion of infections caused by MRSA increased annually, between 1997 and 2006, then decreased between 2006 and 2012.
There were more deaths associated with invasive MSSA infections (237 vs. 110) than MRSA. The mortality rate for both groups, however, was similar at 9.6% in infants with MSSA vs. 11.9% in infants with MRSA (P = .05).
Benjamin and colleagues suggested broadening the scope of S. aureus prevention to target both types of infection.
“Consideration should be given to expanding hospital infection control efforts targeting MRSA to include MSSA as well,” they wrote. “Future studies to better define the relationship between MSSA colonization and subsequent infection will help to clarify the importance of such interventions for preventing MSSA disease.”
In a related editorial, Joseph B. Cantey, MD, of the department of pediatrics at Texas A&M Health Science Center, and colleagues wrote that while targeted surveillance of specific pathogens would be effective at reducing infections, it could result in unnecessary workloads and costs.
“The key to minimizing morbidity and mortality from any organism (S. aureus included) must be prevention of horizontal transmission that can result in NICU outbreaks,” Cantey and colleagues wrote. “We know that horizontal transmission occurs via the hands of health care workers, so hand hygiene as part of standard and transmission-based precautions remains the main stay of prevention. Unlike decolonization practices that focus on a specific organism, hand hygiene provides protection against all pathogens.” – by David Costill
Disclosure: Benjamin reports receiving research support from Cempra Pharmaceuticals.
Perspective
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Ericson and colleagues’ study of invasive MSSA and MRSA infections gives a good perspective on the need to focus on the prevention of MSSA infections as much as we have on MRSA infections as they have similar associated mortality and occur more often. This is in line with the perspective in the NICU for many years, in that while we want to eliminate all infections in our patients, we may have had an imbalance in those we target. For example, gram-negative infections and specifically pseudomonas infections have mortality rates around 50% to 75% in preterm infants weighing less than1,500 g, but little research and infection control studies or measures focus on these infections.
The authors demonstrated the increase in incidence from 1997 to 2007, followed by a decline in both MSSA and MRSA. The rise may be due to care of more infants aged younger than 25 weeks gestation, and the fall may be due to central venous catheter prevention measures (CLABSI bundles). But further research is needed to better define these factors.
Taking a page from CLABSI bundles, antifungal prophylaxis, and early-onset group B streptococcus prevention, well-designed studies should be performed to examine targeted prevention or decolonization with or without surveillance in high-risk patients. Comparing practices at centers with low rates and those with higher rates may help as well. At IDWeek 2015 there were studies showing surveillance and decolonization with mupirocin (Popoola VO, et al.) as well as one targeting mupirocin monthly for 5 days showing a decrease in both invasive MSSA and MRSA infections (Ristagno E, et al.). Neither was a randomized controlled trial. This seems to be the approach in infection control studies, but there is no reason we can’t have a higher level of evidence. Recently we performed a study of nonsterile gloving with patient and catheter care as an RCT, and published our findings demonstrating fewer gram-positive infections in preterm infants.
Studies of general cleaning and bathing are lacking. Chlorhexidine is a strong fast acting broad-spectrum biocide and has become more commonly used in the NICU with central line care and wipes for bathing, but has neuronal toxicity if it comes in direct contact with neurons and still has not had studies that include safety regarding whether there is significant systemic absorption and if that may affect neurodevelopmental outcomes.
Moving forward, our patients in the NICU need well-designed studies examining both efficacy and safety of our interventions to prevent these serious and often fatal diseases. As the authors point out, there are 5,000 infections yearly due to invasive Staphyloccocus aureus infections with approximately 200 associated deaths (using the 7-day mortality) and increased neurodevelopmental impairment in the survivors.
