Despite the many benefits of breast-feeding, breast milk is a biologic product that has the potential to transmit infection. For example, breast milk from a mother who was infected with GBS or S. aureus has been implicated as the vehicle of transmission of these pathogens to infants with resulting severe sepsis (57,58,59). Neonatal sepsis caused by Klebsiella pneumoniae has been associated with contaminated breast milk resulting from the contamination of a component of a breast pump (60), and contamination of a milk bank pasteurizer was associated with an NICU outbreak of Pseudomonas aeruginosa infections (61). Furthermore, viral agents that could be transmitted to infants in breast milk or in the blood contact associated with breast-feeding from dry, cracked nipples include hepatitis B virus (HBV), HIV, and human T-lymphotrophic virus type 1 (HTLV-1). Therefore, in
countries where safe formula for bottle-feeding is readily available, breast-feeding is contraindicated for mothers known to be infected with HIV and HTLV-1. HBV vaccine given to neonates is protective against transmission by breast-feeding. Although cytomegalovirus (CMV) is transmitted in breast milk, maternal antibody is protective against clinically significant disease. The CDC’s guidelines developed for banking human milk obtained from unrelated donors include screening all donors for HIV, HTLV-1, and HBV surface antigen and pasteurization (62.5°C for 30 minutes) of all milk specimens. Bacterial counts of 10⁴ colony-forming units (cfu)/mL or more of nonpathogenic organisms or the presence of gram-negative bacteria (GNB), S. aureus, or α- or β-hemolytic streptococci preclude the use of that milk (62). Established guidelines for human breast milk banks (www.hmbana.org), personal hygiene, and handling and decontaminating the components of breast milk pumps (62) should be followed.

Every healthcare facility that handles expressed breast milk should have a written policy to guide storage and handling. Expressed breast milk should be labeled as soon as it is pumped with at least two identifiers in addition to the date and time, and a dedicated refrigerator/freezer should be used for storage. The American Academy of Pediatrics (AAP) recommends refrigerating milk that will not be used immediately and freezing milk at 0°F or below if it will not be used within 24 hours; previously frozen milk that has been thawed in the refrigerator must be used within 24 hours or discarded (http://www.healthychildren.org/English/ages-stages/baby/breastfeeding/Pages/Storing-and-Preparing-Expressed-Breast-Milk.aspx). Powdered infant formulas are not sterile and pose a risk of infection with organisms such as Cronobacter sakazakii or Salmonella sp. if not handled correctly. The World Health Organization has established guidelines for safe preparation, storage, and handling of powdered infant formulas (http://www.who.int/foodsafety/publications/micro/pif_guidelines.pdf). The key points include hand hygiene and cleaning and sterilizing the feeding-preparation equipment before use, discarding unused refrigerated formula after 24 hours, and using room temperature hang times of preferably no >2 hours for continuous or bolus feeds. The CDC recommends a hang time of not >4 hours for continuous feeds in the NICU (63). The most controversial recommendation made by WHO is to use water >70°C to reconstitute powdered infant formula. This recommendation is supported by laboratory studies demonstrating that higher water temperatures result in greater inactivation of C. sakazakii (64). No clinical data have been published to evaluate the comparative efficacy of different preparation methods. Other stakeholders, including the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition, have argued that such high temperatures adversely affect the vitamins in the formula and therefore cannot be recommended (65). Some have expressed concern about the potential for burns if boiling water is used (66). The AAP recommendations for formula preparation at home call for room temperature water to be added to formula immediately before feeding, as long as a safe water source is available (http://www.healthychildren.org/English/ages-stages/baby/feeding-nutrition/Pages/Sterilizing-and-Warming-Bottles.aspx). This difference from the WHO recommendations likely reflects both the higher risk for invasive infections from C. sakazakii among preterm infants and the practicality of formula preparation for healthy infants in the home.

CONS account for nearly 50% of late-onset HAIs in many reports (3,9,40,41,48,118). Several reasons for the increased recognition of this organism as a neonatal pathogen follow:

The epidemiology of neonatal CONS-BSI has been studied extensively using pulsed-field gel electrophoresis (PFGE), ribotyping, DNA-DNA hybridization, and restriction endonuclease analysis in addition to the traditional methods of speciation, phage typing, and plasmid analysis. PFGE is the most reliable method for confirming the identity of strains. Distinct clones of both Staphylococcus haemolyticus (119,120) and Staphylococcus epidermidis (121,122,123) can become endemic in NICUs, and cause clusters of infections over periods of 6 months to as long as 10 years. At the same time, many completely unrelated strains can be isolated from infants within the same unit. Some NICUs possibly have no related strains identified during a specific period of time (124,125). Eastick et al. (126) have reported relatively stable reservoirs of CONS in the feces, around the ear, and in the axillae and nares but small, unstable numbers on the skin of the forearm and leg. Thus, cross-contamination among sites on the same infant as well as horizontal spread among infants is an important mode of transmission. Infusion of parenteral fluids contaminated with CONS is a rare source of BSI in the NICU (127).

The clinical manifestations of CONS-BSI are most often nonspecific, and this pathogen is rarely considered a cause of death (128). The signs of sepsis observed most frequently are fever, apnea and bradycardia, feeding intolerance, and lethargy. Temperature instability, thrombocytopenia, abdominal distention, and persistent BSI in the absence of a CVC have been associated with disease caused by CONS (129,130). Specific delta toxin-producing strains have been found in pure culture in the stool or in the blood or peritoneal fluid of patients with a mild form of NEC (131,132). Focal infections associated with these pathogens include neck abscess, omphalitis, wound abscess, and mastitis (133). Right-sided endocarditis caused by CONS must be considered in the presence of a CVC, persistent BSI (>48 hours), and thrombocytopenia during appropriate antimicrobial therapy for BSI (134). Physical examination might
reveal no other abnormalities but an echocardiogram could demonstrate vegetations in the right atrium or on the tricuspid valve. Removal of the CVC is required for clearance of CONS if BSI persists for >4 days (135).

After CONS, S. aureus was the second most frequently isolated pathogen from NICU infants in a 1986 to 1993 report (9) and in studies from the Neonatal Research Network (3). In contrast, the point-prevalence study of 29 NICUs performed in 1999 reported that S. aureus accounted for only 3.4% of BSIs (48). Since the late 1980s, S. aureus outbreaks in the NICU have been associated with both MSSA (78,105,136,137,138,139) and MRSA (25,140,141,142,143,144), and reports of outbreaks of MRSA have surpassed those of MSSA in recent years. The incidence of late-onset MRSA infections increased >300% between 1995 and 2004 (145). Nurseries situated in large general hospitals that share services (laboratory, radiology) and HCWs (nurses, respiratory therapists, consulting physicians) are especially vulnerable to the acquisition of virulent strains from geographically distant foci of healthcare-associated MSSA or MRSA infection. A single or multiple virulent strains can be introduced into the nursery by a colonized infant, a visiting family member, and, rarely, an HCW (146,147,148). However, the principal mode of transmission is horizontal via the hands of HCWs who fail to follow recommendations for hand hygiene between patient contacts. PFGE is the most useful method to determine whether a single or multiple strains caused an outbreak (149); a recent study demonstrated the improved efficacy of detecting clonal strains through the use of whole-genome sequencing, although this technique currently remains primarily a research tool (150). High rates of colonization (30% to 70%) can become established before clinical disease is recognized. The clinical and economic impacts of MRSA colonization and infection in NICUs have been quantified in several studies (151,152). Environmental sources or chronic carriers have rarely been implicated in nosocomial transmission in the NICU, but environmental contamination with S. aureus does occur and contributes to the overall burden of pathogens in high-risk units. Unidentified virulence factors and environmental conditions determine the persistence of the organism in the NICU. In Parkland Health and Hospital System’s crowded NICU in Dallas, Texas, MRSA persisted for a 3-year period from 1988 to 1991 (25). Neither susceptible S. aureus nor MRSA nursery outbreaks were controlled until conditions of overcrowding and understaffing were corrected (25,78). Minimizing the number of nurses caring for both MRSA-colonized and -uncolonized infants may be beneficial in reducing MRSA transmission (153). The prevalence of CA-MRSA strains that have antibiotic susceptibility and molecular profiles (staphylococcal chromosomal cassette [SCC] mec types IV or V) distinct from those of the traditional healthcare-associated MRSA strains (149) has increased, and transmission of those CA-MRSA strains have been reported within healthcare facilities (154,155,156). A shift from healthcare-associated MRSA to CA-MRSA in the NICU now appears to be occurring (157

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