Prevention and Management of Neonatal Infections

The Functional DNA Methylation Signatures Relevant to Altered Immune Response of Neonatal T Cells with l-Arginine Supplementation

l-Arginine is an important nutrient in the infant diet that significantly regulates the maturation of the immune system in neonates, including the maturation of CD4⁺ T cells. The biological activities of CD4⁺ T cells differ substantially between neonates and adults, and these differences may be governed by epigenetic processes. Investigating these differences and the causative processes may help understand neonatal and developmental immunity. In this study, we compared the functional DNA methylation profiles in CD4⁺ T cells of neonates and adults, focusing on the role of l-arginine supplementation. Umbilical cord blood and adult CD4⁺ T cells were cultured with/without l-arginine treatment. By comparing DNA methylation in samples without l-arginine treatment, we found that CD4⁺ T cells of neonatal cord blood generally showed higher DNA methylation than those of adults (average CpG methylation percentage 0.6305 for neonate and 0.6254 for adult, t-test p-value < 0.0001), suggesting gene silencing in neonates. By examining DNA methylation patterns of CpG dinucleotides induced by l-arginine treatment, we found that more CpG dinucleotides were hypomethylated and more genes appeared to be activated in neonatal T-cells as compared with adult. Genes activated by l-arginine stimulation of cord blood samples were more enriched regarding immune-related pathways. CpG dinucleotides at IL-13 promoter regions were hypomethylated after l-arginine stimulation. Hypomethylated CpG dinucleotides corresponded to higher IL-13 gene expression and cytokine production. Thus, DNA methylation partially accounts for the mechanism underlying differential immune function in neonates. Modulatory effects of l-arginine on DNA methylation are gene-specific. Nutritional intervention is a potential strategy to modulate immune function of neonates.

Comparison of the Functional microRNA Expression in Immune Cell Subsets of Neonates and Adults

Diversity of biological molecules in newborn and adult immune cells contributes to differences in cell function and atopic properties. Micro RNAs (miRNAs) are reported to involve in the regulation of immune system. Therefore, determining the miRNA expression profile of leukocyte subpopulations is important for understanding immune system regulation. In order to explore the unique miRNA profiling that contribute to altered immune in neonates, we comprehensively analyzed the functional miRNA signatures of eight leukocyte subsets (polymorphonuclear cells, monocytes, CD4⁺ T cells, CD8⁺ T cells, natural killer cells, B cells, plasmacytoid dendritic cells, and myeloid dendritic cells) from both neonatal and adult umbilical cord and peripheral blood samples, respectively. We observed distinct miRNA profiles between adult and neonatal blood leukocyte subsets, including unique miRNA signatures for each cell lineage. Leukocyte miRNA signatures were altered after stimulation. Adult peripheral leukocytes had higher let-7b-5p expression levels compared to neonatal cord leukocytes across multiple subsets, irrespective of stimulation. Transfecting neonatal monocytes with a let-7b-5p mimic resulted in a reduction of LPS-induced interleukin (IL)-6 and TNF-α production, while transfection of a let-7b-5p inhibitor into adult monocytes enhanced IL-6 and TNF-α production. With this functional approach, we provide intact differential miRNA expression profiling of specific immune cell subsets between neonates and adults. These studies serve as a basis to further understand the altered immune response observed in neonates and advance the development of therapeutic strategies.

Handwashing Program for the Prevention of Nosocomial Infections in a Neonatal Intensive Care Unit

Objective:

To evaluate the effects of a hand hygiene program on compliance with hand hygiene and the rate of nosocomial infections in a neonatal intensive care unit (NICU).

Design:

Open trial.

Setting:

A level-III NICU in a teaching hospital.

Participants:

Nurses, physicians, and other healthcare workers in the NICU.

Interventions:

A multimodal campaign for hand hygiene promotion was conducted beginning in September 1998. This program consisted of formal lectures, written instructions and posted reminders regarding hand hygiene and proper handwashing techniques, covert observation, financial incentives, and regular group feedback on compliance. Surveillance of handwashing compliance and nosocomial infections before and during the program was analyzed.

Results:

Overall compliance with hand hygiene improved from 43% at baseline to 80% during the promotion program. The rate of nosocomial infections decreased from 15.13 to 10.69 per 1,000 patient-days (P= .003) with improved handwashing compliance. In particular, respiratory tract infections decreased from 3.35 to 1.06 per 1,000 patient-days during the handwashing campaign (P= .002). Furthermore, the correlation between nosocomial infection of the respiratory tract and handwashing compliance also reached statistical significance (r= -0.385;P= .014).

Conclusions:

Improved compliance with handwashing was associated with a significant decrease in overall rates of nosocomial infection and respiratory infections in particular. Washing hands is a simple, economical, and effective method for preventing nosocomial infections in the NICU

L-Arginine modulates neonatal lymphocyte proliferation through an interleukin-2 independent pathway

In cases of arginine depletion, lymphocyte proliferation, cytokine production and CD3ζ chain expression are all diminished. In addition to myeloid suppressor cells, polymorphonuclear cells (PMN) also exert T-cell immune suppressive effects through arginase-induced l-arginine depletion, especially during pregnancy. In this study, we investigated how arginase/l-arginine modulates neonatal lymphocyte proliferation. Results showed that the neonatal plasma l-arginine level was lower than in adults (48·1 ± 11·3 versus 86·5 ± 14·6 μm; P = 0·003). Neonatal PMN had a greater abundance of arginase I protein than adult PMN. Both transcriptional regulation and post-transcriptional regulation were responsible for the higher arginase I expression of neonatal PMN. Exogenous l-arginine enhanced neonate lymphocyte proliferation but not that of adult cells. The RNA-binding protein HuR was important but was not the only modulation factor in l-arginine-regulated neonatal T-cell proliferation. l-Arginine-mediated neonatal lymphocyte proliferation could not be blocked by interleukin-2 receptor blocking antibodies. These results suggest that the altered arginase/l-arginine cascade may be one of the mechanisms that contribute to altered neonatal immune responses. Exogenous l-arginine could enhance neonate lymphocyte proliferation through an interleukin-2-independent pathway.

Hospital-acquired viral pathogens in the neonatal intensive care unit

Hospital-acquired infections caused by viruses are a cause of considerable morbidity and occasional mortality in critically ill neonates. The intensive care environment allows for efficient spread of viral pathogens, and secondary cases among both patients and healthcare workers are frequently observed. We review the common viral causes of hospital-acquired infections in neonates, including rotavirus, respiratory syncytial virus, and others, discuss epidemiology and clinical syndromes, and summarize recommendations for control in outbreak situations. Chemoprophylaxis, isolation procedures, and care of affected staff are also addressed.

Outbreak investigation in a neonatal intensive care unit

Outbreaks of healthcare-acquired infection can be devastating in neonatal intensive care units. Neonates are especially susceptible hosts because of prematurity of organ systems, low birth weight, and the use of invasive devices. This article outlines methodologies for infection surveillance and recognition of outbreak events. Principles of infection control in the neonatal intensive care unit are reviewed in reference to an outbreak setting, and a multidisciplinary team approach to developing a plan of action to halt the outbreak and find the source is discussed. Epidemiologic methods for determining the geographical extent and timeline of an outbreak, potential reservoirs or a common source of infection are reviewed.

[Risk factors associated with nosocomial bacteremia in low birth weight neonates. Grady Memorial Hospital, Atlanta]

BACKGROUND

Nosocomial bloodstream infections occur frequently in Neonatal Intensive Care Units and are associated with recognized and unrecognized risk factors. Little has been published regarding risk factors for bloodstream infections in low birth weight neonates.

OBJECTIVE

To investigate risk factors for bloodstream infection in neonates < 1,500 g admitted at a Neonatal Intensive Care Unit.

METHODS

A prospective study was undertaken in low birth weight neonates (< 1,500g) during a 22 months period. Bivariant, and logistic regresion (stepwise procedure) analysis was used to determine the significance association of bloodstream infection and perinatal and nosocomial risk factors.

RESULTS

A total of 72 patiens with nosocomial bacteriemia and 147 non bacteriemic patients were studied. Independent risk factors associated with bloodstream infection were birth weight, persistence of umbilical catheter > 7 days and persistence of peripheral arterial catheter > 1 day.

CONCLUSIONS

The uses of umbilical catheter > 7 days, peripheral arterial catheter > 1 day and birth weight < 1,500 g were significant determinants of nosocomial bloodstream infection risk. Because of the importance of invasive procedures as a source of nosocomial bloodstream infections, the lines duration needs to be reviewed with the aim of reducing the incidence of blood stream infection.

Classification and risk-factor analysis of infections in a surgical neonatal unit

BACKGROUND/PURPOSE

Nosocomial infection may result in significant morbidity in surgical neonates. Traditionally, nosocomial infections are classified using time cut-off points. Gastrointestinal carriage of microorganisms has not been used as a criterion for classifying infection in surgical neonates. The aims of the study were to (1) determine the overall infection rate, (2) distinguish between nosocomial and community acquired infections using a 48-hour postadmission cutoff and the carrier state criterion, and (3) determine risk factors for clinical infection.

METHODS

A 1-year prospective observational cohort study was undertaken in a regional neonatal surgical unit between 1997 and 1998. All infants residing for >/=3 days in the unit were included in the study (n = 167). Patient demographics, including illness severity (PRISM score), were recorded for all infants. Surveillance throat and rectal swabs were obtained on admission and twice weekly thereafter to determine carrier status. Carriage was defined as isolation of the same microorganism from at least 2 consecutive surveillance samples. Infective episodes were diagnosed if a clinical diagnosis of local or general inflammation was microbiologically proven.

RESULTS

A total of 167 infants responsible for 174 admissions were studied. Median gestational age was 38 weeks (range, 24 to 42), median birth weight was 3 kg (range, 1 to 3.6), median age on admission was 8 days (range, 0 to 142), median length of hospital stay was 8 days (range, 3 to 95). The diagnoses were gastrointestinal disorders (n = 96), abdominal wall defects (n = 22), neural tube defects and hydrocephalus (n = 17), thoracic disorders (n = 16), urologic disorders (n = 12), and abdominal tumours (n = 4). Twenty-five infants had 33 episodes of infection giving an overall infection rate of 14.9%. The predominant infecting organism was Stapylococcus aureus (n = 11); others were enterococcus, coagulase negative staphylococcus, Candida spp, Gram-negative bacilli, and anaerobes. A total of 27 of 33 infective episodes were caused by microorganisms carried by the infants on admission (primary endogenous). Only 6 children had "true" nosocomial infections. Using a traditional 48 hour cutoff, 87% of the infections were classed as nosocomial. Birth weight, presence of central venous line, PRISM score, and length of stay were identified as significant risk factors for developing clinical infection.

CONCLUSIONS

(1) Carriage allowed us to identify the true nosocomial infection rate (microorganisms acquired in the unit), which was only 18%. In contrast, using a traditional 48 hour cutoff, 87% of the infections would have been classed as nosocomial and warranted unnecessary cross-infection investigations. (2) The results of this study confirm that birth weight, illness severity (PRISM score), presence of central venous catheter, and length of hospital stay were independent risk factors associated with clinical infection in surgical neonates.

Cross infections due to coagulase-negative staphylococci in high-risk patients

Until recently, infections due to coagulase-negative staphylococci (CNS) have been regarded as endogenous in origin. However, there are now increasingly reports in the literature on the endemic occurrence of distinct strains of CNS. Several outbreaks due to CNS are reported in cardiac surgery or in neonates. The latter seem to be high risk populations in regard to CNS infections because of certain risk factors (i.e. degree of immunosupression, routine use of central venous catheters and parenteral lipids as well as broad spectrum antibiotic therapy). On the other hand, these newborn babies have no physiological skin flora and are therefore easily colonized by multiresistent bacteria. The persistence of certain well-defined Staphylococcus epidermidis (SE) strains in neonatal intensive care units have been demonstrated over periods as long as a decade. Specific putative virulence factors (i.e. slime production and polysaccharide/adhesin PS/A) were more common in endemic strains as compared to single isolates. Pulsed-field gel electrophoresis (PFGE) proves to be a powerful tool in the study of the epidemiology of CNS while other modern typing techniques (ribotyping, plasmid typing) were also used in the literature to investigate outbreaks of CNS infections.

Reducing the spread of antimicrobial-resistant microorganisms. Control of vancomycin-resistant enterococci

Strategies to reduce the spread of hospital-acquired microorganisms resistant to multiple antimicrobial agents are discussed. Because hospitals have experienced a rapid increase in the incidence of infection and colonization with vancomycin-resistant enterococci (VRE) in the past 5 years, the Hospital Infection Control Practices Advisory Committee of the Centers for Disease Control and Prevention has issued recommendations for preventing the spread of vancomycin resistance. Controlling VRE dissemination in pediatric patients requires prompt detection of VRE by microbiology laboratories, education of staff and families about VRE, use of infection control measures to prevent person-to-person VRE transmission, and prudent vancomycin use.

Importance of the environment and the faecal flora of infants, nursing staff and parents as sources of gram-negative bacteria colonizing newborns in three neonatal wards

Gram-negative bacteria are an important cause of invasive infection among neonates. In this study a novel fingerprinting method was used for the first time to assess the importance of various potential reservoirs of the major gram-negative enterobacteria that colonized 46 consecutive infants in three neonatal special care units during a three to four week period. Such bacteria were isolated from the oropharynx, umbilical cord and faeces in 24%, 33% and 100% of the infants, respectively. Klebsiella/Enterobacter spp. dominated over Escherichia coli and spreading (shared) over sporadic strains. Sixty-one percent of the neonates were colonized with at least one and up to six different strains shown to exist in the ward, mainly in other infants. Environmental reservoirs and the faecal flora of mothers and staff were of minor importance. Vertical transmission occurred in 12% of vaginally delivered infants and in 0% of those delivered by caesarean section.

Intravenous immune globulin for the prevention of nosocomial infection in low-birth-weight neonates. The Multicenter Group for the Study of Immune Globulin in Neonates

BACKGROUND

Nosocomial infection is a major risk for premature infants with very low birth weights. One reason for their susceptibility to infection may be antibody deficiency, since there is little transfer of maternal IgG to the fetus before 32 weeks' gestation.

METHODS

We conducted a multicenter, double-blind study of neonates weighing 500 to 1750 g at birth. A total of 588 neonates were randomly assigned, with stratification for birth weight, to receive periodic intravenous infusions of either immune globulin (500 mg per kilogram of body weight per day) or a placebo. Mortality, morbidity, and nosocomial infection during the next 56 days were assessed.

RESULTS

The infusions were well tolerated; mild, reversible adverse reactions occurred in five infants in each group. There was a significant reduction in the risk of a first nosocomial infection in the recipients of immune globulin as compared with the placebo recipients (relative risk, 0.7; 95 percent confidence interval, 0.5 to 0.9). About 85 percent of the nosocomial infections were bacterial; the majority of these were caused by coagulase-negative staphylococci or Staphylococcus aureus. The neonates who received immune globulin had fewer mean days of hospitalization than the controls (62 vs. 68, P = 0.15); among the infants with infections, the difference in the mean length of the hospital stay was even greater (80 days vs. 101 days, P = 0.02).

CONCLUSIONS

For premature infants weighing between 500 and 1750 g at birth, treatment with intravenous infusions of immune globulin is safe and reduces the risk of nosocomial infection.

Comparison of rates of nosocomial infections in neonatal intensive care units in the United States. National Nosocomial Infections Surveillance System

To determine nosocomial infection (NI) rates among neonatal intensive care units (NICUs) that are useful for interhospital comparison, we analyzed data reported in 1986-1990 from 35 hospitals that have level III NICUs and used standard National Nosocomial Infections Surveillance protocols and NI site definitions. Overall rates of NI were calculated as the number of NI per 100 patients (overall NI patient rates) or the number of NI per 1,000 NICU patient-days (overall NI patient-day rates). A strong positive association was found between overall NI patient rates and the neonates' average length of stay, a marker for duration of exposure to important risk factors. No correlation was found between overall NI patient-day rates and average length of stay. However, a strong positive correlation between overall NI patient-day rates and a measure of device utilization (total device-days/total patient-days x 100) was found. Additionally, a positive correlation between overall NI patient rates and device utilization was found. Stratification among the three birthweight groups (less than 1,500 g, 1,500-2,500 g, greater than 2,500 g) did not eliminate the need to control for variations in these factors among NICUs. Device-associated, device-day infection rates, calculated as the number of umbilical or central line-associated blood-stream infections per 1,000 umbilical or central line-days and the number of ventilator-associated pneumonias per 1,000 ventilator days, were not correlated with a unit's site-specific device utilization. These data suggest that calculation of device-associated NI rates in NICUs using device-days as the denominator helps to control for the duration of exposure to the primary risk factor and will be more meaningful for purposes of interhospital comparison.