Characterization of early activation events in cord blood B cells after stimulation with T cell-independent activators.

Human neonates are immunologically immature, particularly in their humoral antibody responses to T cell-independent antigens, as exemplified by their increased susceptibility to infections with polysaccharide-encapsulated bacteria. To clarify the mechanism(s) underlying the unresponsiveness of neonates to polysaccharide antigens, we used an in vitro model with neonatal cord blood cells that has been shown to mimic surface Ig-dependent signaling in the adult by T cell-independent antigens. We studied the ability of cord blood human B cells to become activated after ligation of their surface Ig by unconjugated anti-Ig, dextran-conjugated anti-Ig, and Staphylococcus aureus Cowan A1, and compared their response with that of adult B cells. After the addition of nanogram concentrations of anti-Ig-dextran, neonatal cord blood B cells proliferated at levels comparable to that observed with adult B cells. The majority of cord blood B cells showed a marked rise in intracellular calcium, increased surface expression of human leukocyte antigen DR, and an increase in cell size. Direct activation of protein kinase C by phorbol esters in neonatal B cells led to cellular proliferation, and when combined with anti-Ig, a synergistic effect on proliferation was observed. These data suggest that the unresponsiveness of human neonates to polysaccharide antigens does not represent an inability of these antigens to induce early activation events in circulating B cells.

Use of human milk in the intensive care nursery decreases the incidence of nosocomial sepsis.

OBJECTIVES: This study compares stool colonization and incidence of sepsis in human milk-fed (HM) and formula-fed (FF) intensive care nursery (ICN) patients. STUDY DESIGN: Infants recruited prospectively were fed HM based on the decision of their mothers (59 HM and 114 FF). The incidence of sepsis was determined during the following three intervals: period 1, first 10 days of life; period 2, 11 to 24 days; and period 3, 25 to 38 days. RESULTS: Frequency of Escherichia coli and Enterococcus sp. colonization was increased in HM infants. The incidence of sepsis was 9.5% in period 1 (5% in HM vs 10% in FF), 17.2% in period 2 (9% in HM vs 20% in FF), and 12.5% in period 3 (0% in HM vs 15% in FF). The odds ratio for sepsis in HM infants was 0.4, the 95% limits 0.15 to 0.95, p = 0.04. CONCLUSIONS: HM feeding in the ICN has a protective effect against nosocomial sepsis, which is unrelated to its influence on gastrointestinal (GI) flora.

Staphylococcus epidermidis sepsis in the intensive care nursery: a characterization of risk associations in infants < 1,000 g.

We undertook to determine Staphylococcus epidermidis colonization patterns and risks of sepsis in a cohort of 82 consecutive intensive care nursery admissions (birth weight 1,285 +/- 57 g), with 24 infants weighing < 1,000 g at birth. Colonization was determined by skin and stool cultures collected at three time points. Multiple neonatal variables were classified into three intervals preceding the time of sample collection including the occurrence of S. epidermidis sepsis. 16 infants (20%) developed S. epidermidis sepsis. 81% of these episodes occurred in infants < 1,000 g. Skin colonization was nearly universal at all sampling points. Rectal colonization was 63.6% initially (10 +/- 0.4 days), then declined to 32% by the third sample (37 +/- 0.4 days). Neither prevalence of skin nor rectal colonization influenced the incidence of sepsis significantly. Statistically significant risk associations for sepsis for the entire intensive care nursery population included: low birth weight, gestational age, presence of a central line, and delayed feeding. For infants < 1,000 g the occurrence of sepsis during the second study time period (54% of the episodes) was associated with preceding steroid exposure. During the third study time period, birth weight and delayed attainment of full enteral feeds showed a statistically significant association with sepsis. We conclude that infants < 1,000 g are at an increased risk of S. epidermidis sepsis. Extreme immaturity, steroid therapy, and prolonged hyperalimentation are all significant risk associations.

Incidence of Candida parapsilosis colonization in an intensive care nursery population and its association with invasive fungal disease.

We have studied 82 consecutive intensive care nursery admissions to determine rates of colonization and incidence of fungal sepsis. Cultures were obtained from stool, gastric aspirate and skin at three different times. Infants studied ranged in gestational age from 23 to 38 weeks (mean +/- SEM 29 +/- 0.4 weeks). Nineteen percent of all infants were colonized with Candida sp.; stools were more frequently culture-positive than skin or gastric aspirates. Colonized infants began enteral feeds at a later time compared with noncolonized neonates. Five of the study infants developed fungal sepsis. One had congenital Candida albicans sepsis and died at 10 days of age; the other four had Candida parapsilosis sepsis and survived. The development of C. parapsilosis sepsis was significantly associated with gastrointestinal colonization. Our results suggest that early initiation of enteral feeds decreases gastrointestinal colonization with C. parapsilosis. Gastrointestinal colonization was strongly associated with the subsequent development of C. parapsilosis sepsis in this group of high risk neonates.

Bacterial contaminants of collected and frozen human milk used in an intensive care nursery.

BACKGROUND: Use of human milk for preterm and high-risk neonates conveys many potential benefits but also poses practical difficulties. This prospective study examined the prevalence and degree of bacterial contamination of human milk used in the intensive care nursery. METHODS: One hundred eight milk samples collected from 40 mothers were tested for contamination. Samples from mothers whose milk showed a high degree of contamination were retested after counseling on collection methods. RESULTS: Only 12.5% of the samples showed no bacterial growth. Of the contaminated samples, 38% contained > 30,000 colony-forming units/ml. The most common contaminants were Staphylococcus epidermidis (82%) and Acinetobacter (9%), but other contaminants were also encountered. CONCLUSIONS: There were not statistically identifiable common characteristics of mothers whose milk showed abundant bacterial contamination. Only 30% of these mothers showed improvement in the degree of contamination after counseling regarding techniques of milk collection.

Aerobes isolated in fecal microflora of infants in the intensive care nursery: relationship to human milk use and systemic sepsis.

BACKGROUND: Staphylococcus epidermidis is a leading cause of nosocomial sepsis in the intensive care nursery. The relationship between rates of gastrointestinal colonization and the incidence of systemic sepsis with S. epidermidis in hospitalized neonates is under investigation. METHODS: In this study, we enrolled 46 infants consecutively admitted to the intensive care nursery (mean +/- standard deviation, birth weight 1300 +/- 337 gm, gestational age 29.4 +/- 2.2 weeks). At the time of enrollment, infants had been fed enterally for at least 1 week (28 were fed formula and 18 received their own mothers' frozen milk). Stool samples were collected when infants were 2 to 3 weeks of age (16.3 +/- 7.4 days). RESULTS: Aerobic stool flora were present in 65% of all patients. Human milk use was associated with a significant increase in the presence of aerobic stool flora (78% vs 46%, p = 0.035), as well as more frequent isolation of S. epidermidis. The incidence of S. epidermidis sepsis was 33% in those infants whose stool specimens grew S. epidermidis and 3.5% in those whose stool specimens did not (p < 0.01). CONCLUSIONS: These findings suggest the gastrointestinal tract as a possible site of entry for S. epidermidis in the hospitalized preterm infant. In addition, frozen human milk may be a vehicle for gastrointestinal S. epidermidis colonization.

Prevalence and toxigenicity of Clostridium difficile isolates in fecal microflora of preterm infants in the intensive care nursery.

Fecal isolates of Clostridium difficile and its toxin B were followed prospectively in 50 preterm intensive care nursery (ICN) patients. The first stool specimen was obtained after 1 week of enteral feeding, at 15 +/- 1 days of life, and 2 more specimens were collected at 2-week intervals, 24 +/- 1 and 32 +/- 2 days of life. The stools were cultured for C. difficile, and tested for C. difficile toxin B. In the first specimen 15% of stools grew C. difficile. In the second specimen C. difficile isolation rates increased to 33% and plateaued. Toxin B was detected in 71, 93 and 100% of culture-positive stools in the first, second, and third specimens, respectively. C. difficile colonization was not associated with a higher incidence of necrotizing enterocolitis or diarrhea, and using precollected, frozen human milk did not protect from C. difficile colonization.

Impaired interferon-alpha enhancement of neonatal monocyte phagocytosis.

Monocyte phagocytic activity was tested in 10 healthy term newborns using a latex phagocytic assay. The baseline phagocytic activity in the cord blood monocytes (37.7 +/- 3.8%) was comparable to adult controls (38.5 +/- 9.4%). When enhanced with 1,000 U/ml of alpha-interferon, the phagocytic activity was lower in cord blood monocytes (40.5 +/- 3.4%) than in the adult controls (47.9 +/- 10.6%), but this difference reached statistical significance only when the cord blood monocytes were enhanced with 2,000 U/ml reaching 43.6 +/- 4.3% in cord blood monocytes, as compared to 54.6 +/- 9.6% in adult controls. These findings may explain an inherent functional deficiency in the neonatal mononuclear phagocytic system which may not be evident during the quiescent phase of monocyte/macrophage activity, but may become apparent during an infectious challenge.