MRSA infection in neonatal intensive care units

Methicillin-resistant S. aureus strains increased in the U.S. from 2.4% in 1975 to 29% in 1991. Once established, MRSA is very difficult to eradicate. One of the biggest challenges is preventing cross-transmission of these organisms. Certain patients are more prone to infection and colonization by MRSA, and neonates in NICUs are a high-risk group (Finkelstein, 1999, 24).

Risk factors for acquiring MRSA include prolonged hospitalization; a stay in an ICU or burn unit; previous antimicrobial therapy; surgical site infections; and exposure to colonized or infected patients. The majority of MRSA infections in neonates are primary bacteremias and pneumonias. MRSA infections have also been associated with increased morbidity and mortality, and greater hospital costs than those due to methicillin-sensitive Staphylococcus aureus (MSSA).

Why are neonates more prone to MRSA infection?

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With regards to skin infection it has been shown that an infant's gestational age has a great impact on epidermal barrier function as measured by transepidermal water loss. Preterm infants younger than 28 weeks show decreased functioning of the epidermal barrier, placing them at risk for cutaneous bacterial infection (Kalia, 1998, 323). The skin barrier attains full function, similar to adult skin, by 2 to 4 weeks of age but can take as long as 8 weeks in extremely premature infants. Mandel et al. (2004, 161) conducted a retrospective analysis of the role of cutaneous abscess in sepsis. They found that in 22% of the newborn infants with nosocomial sepsis, cutaneous abscess was the underlying cause.

Additionally, their immune systems are underdeveloped, with white blood cells-neutrophils in particular-moving more slowly than adults'. It's suspected that neonates become colonized with S. aureus soon after being placed in a nursery, with the umbilical stump as the site of initial colonization. Factors identified with MRSA outbreaks in NICUs include high infant-to-staff ratios and infection transmission through hand carriage by health care workers (AAP, 1997)

Spread of MRSA Infection and prevention

MRSA is found on the anterior nares, groin, and perineum, S. aureus is a normal part of the body flora. It's also a common pathogen, causing major infections in both compromised and uncompromised patients. The normal immune response of the body can overcome any MRSA attempt to infection, but in the intensive care due to reduced immune response, and bacterial resistance, these organisms van create havoc. In a report from Australia quoted by Park (2007, 26-27), it was shown that from 1992 to 1994, methicillin-resistant S. aureus (MRSA) infections caused only 8% of staphylococcal infections but from 1995 to 1998, there was an outbreak of MRSA infection in two Melbourne hospitals.

Methods to halt the spread of MRSA outbreaks include reducing overcrowding and improving staffing patterns, treating umbilical cords with triple-dye, and bathing full-term infants with hexachlorophene. But unless strict adherence to infection control is maintained, it is not possible to control this infection. Handwashing is most important. The American Academy of Pediatrics recommends that neonatal nursery staff perform a three-minute handwash at the start of each shift, cleansing up to the elbows with an antiseptic soap and sponge brush (AAP, 1997).

Infected neonates should be placed on contact precautions. Here the infant must be handled with gloves, and if possible, depending on the spacing available and the acute status of the infant, they should be assigned to isolated chambers (Larson, 1995, 259, 262). Hitomi etal (2000, 127), advocate the use of mupirocin as a nasal spray to control nasal carriage of MRSA in the hospital staff, which act as the greatest source of spread of this infection.

Effects of Nosocomial MRSA infection

According to the NNIS (2002), In 2000, 55.3% of S. aureus isolates causing nosocomial infections among patients hospitalized in intensive care units in hospitals reporting to the National Nosocomial Infection Surveillance System were resistant to methicillin. Nambiar etal(2003, 224) give an interesting account of the complications MRSA can cause in an intensive care setting. They describe an outbreak of MRSA, in which neonates had meningitis, blood stream infection (with its complications - soft tissue abscess, shock and a right atrial thrombus, suppurative thrombophlebitis, osteoarthritis of the distal femur and knee joint). Masanga (1999, 169) reported colonic stenosis after MRSA enterocolitis.

The predisposing factors for neonatal MSSA enterocolitis include breast feeding from a mother with staphylococcal mastitis,an indwelling feeding catheter  and malnutrition. The clinical picture of MSSA enterocolitis in the neonate is characterized by acute onset of diarrhea and ileus.

Necrotizing enterocolitis. intensive care including mechanical ventilation, indwelling feeding catheter, the use of antibiotics, the delay of feeding causing the lower acidity of gastric contents, hypoactive peristalsis and the change of bowel flora, conditions similar to those seen in postoperative patients most likely predisposed to abnormal MRSA growth and resultant enterocolitis. toxic shock syndrome (combination of erythema and thrombocytopenia, low-positive C-reactive protein (CRP) value, or fever), (Richtmann etal, 2000, 88-89, Takahashi, 2003, 234-35).

Effect on parents

The illness in the neonate is a great source of stress to the parents. Not only is the child separated from the mother, which leads to anxiety for the mother, and nursing problems. There occur problems of lactation, with breast engorgement and galactorrhoea. In addition, the mother is at a greater risk of catching infection from a septicemic child with pneumonia and exanthemas. Skin infection can spread via contact. Thus parents are at an increased risk from a child affected with MRSA infection.

Treatment

Prevention is the best treatment. This infection can be rapidly fatal in the neonates, particularly the preterm infants. Prompt recognition of the symptoms and active measures to prevent spread can reduce the morbidity and mortality. Cultures should be obtained for susceptibility determination in any child with a presumed S. aureus infection that is moderate to severe. The choice of empiric therapy, before susceptibility testing, and the choice of definitive therapy will depend on the local antibiotic resistance patterns, the tissue site and severity of infection, and the toxicity profile of the antibiotic.

Vancomycin has been the traditional antibiotic employed for the treatment of MRSA pneumonia. It has been found, however, that problems with lung tissue penetration may limit the effectiveness of vancomycin  Similarly, daptomycin has been shown to have limited activity for pneumonia due to limited lung penetration and inhibition by surfactant. Linezolid has also recently been evaluated as a specific treatment for MRSA pneumonia, and found to have good lung tissue penetration capability (Bradley, 200575-77)

Conclusions

MRSA infection in the neonatal intensive care setting is associated with exceptional morbidity and mortality. Preventive measures are the key to victory against MRSA. Each unit has to chart out effective protocols of infection control and adhere to it with a strong will.

References

1 Finkelstein LE etal(1999MRSA in NeonatesAm J Nurs, Volume 99(1).January.24

2  Kalia YN, Nonato LB, Lund CH, et al(1998) Development of skin barrier function in premature infants. J Invest Dermatol; 111:320-326

3 Mandel D, Littner Y, Mimouni FB, et al.( 2004) Nosocomial cutaneous abscesses in septic infants. Arch Dis Child Fetal Neonatal Ed; 89:F161-F162

4 American Academy of Pedaitrics and American College of Obstetricians and Gynecologists (1997)Guidelines for Perinatal care, 4th ed. Elk Grove Village, IL, The Academy,

5 PARK CH etal(2007). Changing trend of neonatal infection: Experience at a newly established regional medical center in KoreaPediatr Int, Volume 49(1).24–30

6 Larson, E. L(1995). APIC guideline for handwashing and hand antisepsis in health care settings. Am.J. Infect.Control 23:251-269.

7  Hitomi S, Kubota M, Mori N, et al(2005): Control of methicillin resistant Staphylococcus aureus outbreak in a neonatal intensive care unit by unselective use of nasal mupirocin ointment. J Hosp Infect; 46: 123–129

8 National Nosocomial Infections Surveillance (NNIS) System Report. Data Summary from January 1992 to June 2001. Issued August 2001. Available at: http://www.cdc.gov/ncidod/hip/NNIS/members/members.htm #nnisreports. Accessed Mar 5 2007

9  Nambiar S, Herwaldt LA, Singh N (2003). Outbreak of invasive disease caused by methicillin-resistant Staphylococcus aureus in neonates and prevalence in the neonatal intensive care unit. Pediatr Crit Care Med, Volume 4(2).220-226

10 Masanga K etal (1999). Colonic Stenosis After Severe Methicillin-Resistant Staphylococcus Aureus Enterocolitis In A Newborn. Pediatr Infect Dis J, Volume 18(2).169-171

11 Richtmann R etal.(2000) Outbreak Of Methicillin-Resistent Staphylococcus Aureus (Mrsa) Infection On A Neonate Intensive Care Unit (Nicu): The Key Role Of Infection Control Measures. Am J Infect Control, Volume 28(1).February 88-89.

12 Takahashi N (2003). Neonatal toxic shock syndrome-like exanthematous disease (NTED). Pediatr Int, Volume 45(2).233–237

13 Bradley JS (2005). Newer antistaphylococcal agents Curr Opin Pediatr, Volume 17(1).71-77

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