1174 infection control & hospital epidemiology october 2015, vol. 36, no. 10


methods Study Location


The NICU at St. Louis Children’s Hospital has 73 beds that can flex to 81 beds during times of high census. Thirty-six beds are in single-patient rooms while 3 open-unit areas have 9 or 14 beds, with flexible beds organized in an 8-bed open-unit model. Open-unit and single-patient rooms were staffed by the


same groups of nurses, residents, nurse practitioners, fellows, and attending physicians. Patients were assigned to 1 of 4 multidisciplinary teams. Nurse-to-patient staffing ratios are 1:1–3, depending on illness severity, and all patients in a nursing assignment are in the same bed configuration. Staffing was similar across bed configurations. Bed assignment was based on staffing and bed availability without regard to diagnosis, acuity, or bed configuration.


Patients


All patients who resided in the NICU from July 1, 2009, to November 30, 2011, were included, regardless of admission or discharge date. The study was approved by the Washington University Human Research Protection Office.


Data Acquisition


Billing and coding data from the hospital management informa- tion system were retrospectively queried for the study interval to determine dates of birth, admission, discharge and death, room location, sex, race, ethnicity, insurance type (Medicaid, private, uninsured), as well as International Statistical Classification of Disease, Ninth Revision, diagnosis codes that contain gestational age and birthweight information. Additionally, data were gathered from the hospital infection control service to identify all patients colonized with MRSA during the study period and the rates of hand hygiene compliance during patient encounters. Apgar score, temperature on admission, and initial blood gas results were gathered from our NICU’s National Institute of Child Health and Human Development data set10 and the Clinical Investigation Data Exploration Repository.11 Finally, patient-specific information regarding all positive cerebro- spinal fluid and blood cultures from NICU patients for the study interval was provided by the microbiology laboratory information system (Cerner Millennium). Hospital management information system data included


daily roomassignments, allowing for each patient’sNICUroom assignment and bed configuration type to be tracked on a day- by-day basis. Patients who transferred between open-unit and single-patient rooms had all data removed from the analyses.


MRSA Genotyping


Anterior nares swab specimen cultures were used to screen for MRSA colonization as part of routine infection control


measures on admission and weekly thereafter, per institution protocol. The first MRSA recovered from each subject was frozen for future analysis. DNA was extracted from bacterial isolates using the BiOstic Bacteremia DNA Isolation Kit (MoBio Laboratories) according to themanufacturers’ directions. Repetitive sequence polymerase chain reaction was then per- formed as previously described, using approximately 100 ng of DNA, a Ready-to-go RAPD analysis bead (GE), and primer RW3A in a final reaction volume of 25 µL.12,13 The repetitive sequence polymerase chain reaction products were resolved using the Agilent 2100 Bioanalyzer, and banding patterns were analyzed using Diversilab software, version 3.4 (bioMérieux), to measure strain similarity. Isolates with similarity indices greater than 95% were considered identical. The Diversilab software compared the DNA banding


pattern of each isolate to all other isolates and assembled this into a 2-dimensional scatterplot. Those with high similarity indices clustered closer than those with low similarity indices. This allowed visualization of genotype clustering within a set of isolates.14


Barrier Precautions


All patients, regardless of MRSA colonization status, were cared for using standard precautions. In addition, infants colonized with MRSA were placed in contact isolation. These policies applied to all members of the staff, families, and visitors. No visitor restriction occurred for either group of patients. Use of alcohol foamor hand washing stations on roomentry and exit is standard of care. Compliance with hand hygiene was assessed by direct observation of repeated patient encounters by members of the hospital infection control committee and included all pro- viders. Observations of compliance occurred weekdays during the day shift and covered all areas of the NICU. A provider who exited one bed space, performed hand hygiene, and entered another bed space remained compliant as long as no other sur- faces were contacted during this transition.


Definitions Confirmed Late-Onset Sepsis Confirmed late-onset sepsis (CLOS) was defined as a having


a culture-positive bacterial infection of the blood or cere- brospinal fluid on or after 72 hours of life for which the patient was treated with antibiotics for 5 or more days.3,15 Episodes of positive bacterial cultures not meeting this definition and nonpathogenic bacteria typically considered contaminants were removed from further analysis.


Illness Severity Indices Maximum Acuity Score. Acuity scores were based on level


of care required by each patient and consisted of type and level of ventilator assistance, presence or absence of central lines, need for and frequency of laboratory draws, and patient monitoring.


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