Studies show that methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S aureus (MRSA) are still significant pathogens in the neonatal intensive care unit, especially for extremely premature infants.1

A recent study presented at the 2015 St. Jude/PIDS Pediatric Infectious Diseases Research Conference in Memphis, Tennessee, found that MSSA infections are much more common than MRSA infections, although each type of infection had a similar mortality risk.  

Jessica E. Ericson, MD, pediatric infectious disease specialist at Penn State Hershey Children’s Hospital  and colleagues (then at Duke University Medical Center) defined S aureus cultures as invasive or noninvasive infections and then did a comparison to determine the proportion of cultures that were MRSA.


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Researchers found that 29% of the infections were MRSA, while MSSA infections made up 71% of the cases. Investigators also found that infants with MRSA and MSSA had about the same odds of death.   

“I hope these results lead doctors to have more concern and awareness for MSSA infections, rather than only focusing on MRSA. It is important to consider both kinds of S aureus infections as we develop new treatment and prevention strategies,” says Dr Ericson.

Risk Factors for Infection

Premature and hospitalized infants are at greatest risk for S aureus infection.

Aaron Milstone, MD, associate professor of infectious diseases at Johns Hopkins Children’s Center in Baltimore, Maryland, found that “in healthy neonates that go home from the nursery, about 40% will be exposed to Staphylococcus within the first few months of life, but the risk of infection is very small. In hospitalized neonates, the risks are much higher.”

“Smaller, more premature infants are at the highest risk,” says Dr Ericson. “We found that infants [weighing] less than 1500 g (about 3 lb) have a risk of invasive S aureus infection of 2.2%, while for infants [weighing more] than 1500 g, or 3 lb, the risk of invasive infection is reduced to 0.1%.”

However, researchers found no major differences in risk factors for MRSA or MSSA infection. According to Dr Ericson, “We found that there aren’t significant differences in risk factors for MRSA as compared with MSSA infections. Prior to the onset of infection, both groups had the same amount of time on a ventilator, similar exposure to antibiotics, similar need for blood pressure support, same amount having a surgery before their infection, and similar gender distribution,” says Dr Ericson. “There was nothing about an infant that predicted he or she would have MRSA infection instead of MSSA.”

Limited Data on Treatment Options for Neonates

Both Dr Milstone and Dr Ericson believe it is important to reduce the incidence of these infections because of concerns about antibiotic treatment in newborns. Dr Milstone says that although there are a number of drugs to treat MSSA and MRSA, newer drugs have limited data in children with regard to dosing, efficacy, and safety. “We are not sure of the right doses, and the antibiotics for MRSA are more toxic and harder to use, especially in very small infants, which is why our main goal is prevention,” says Dr Ericson.

Further Steps to Reduce MSSA and MRSA

To reduce the number of MSSA and MRSA infections, Dr Milstone says that “we need to continue to optimize infection-control measures to prevent the spread–hand washing and environmental cleaning. More data are needed to determine the safety and efficacy of decolonization (reducing asymptomatic carriage of the bacteria) and its safety and effectiveness in reducing infections in neonates exposed to the bacteria.”

Furthermore, Dr Ericson says, “We have found that changing our practices on how central lines are used and removing central lines as soon as possible is very important. In addition, reducing unnecessary antibiotic use is especially important, so there are not as many resistant organisms in the community.”

Medically reviewed by Pat F. Bass III, MD, MS, MPH.

References

1.     Carey AJ, Duchon J, Della-Latta P, Saiman L. The epidemiology of methicillin-susceptible and methicillin-resistant Staphylococcus aureus in a neonatal intensive care unit, 2000-2007. J Perinatol. 2010;30(2):135-139.

2.     MSSA infections surpass MRSA, match mortality risk among infants. Healio. http://www.healio.com/pediatrics/mrsa/news/online/%7B1ffa743e-7c6f-4085-8447-3dcca0f270fb%7D/mssa-infections-surpass-mrsa-match-mortality-risk-among-infants. Accessed August 29, 2015.