802 infection control & hospital epidemiology july 2017, vol. 38, no. 7


Disease Control and Prevention (CDC) to identify risk factors for transmission and provide recommendations to prevent additional cases. Herein, we present findings and recommendations from the CDC investigation.


methods Case Definition and Case Finding


We defined a case as the first positive P. aeruginosa culture from a clinical or surveillance specimen in a patient admitted to the NICU between June 1, 2013, and September 30, 2014. Cases were identified through hospital microbiology record review. We classified cases as either clinical or surveillance based on the indication for testing. Surveillance specimens were collected during periods when unit policy mandated weekly cultures for all patients. This policy was in effect from November 26, 2013, to January 31, 2014, and from August 29, 2014, to September 30, 2014. Certain surveillance cultures were collected outside these periods at provider discretion.


Infection Control Assessment


We conducted observations of NICU infection control and clinical care. We conducted >10 hours of hand hygiene audits at 30–120 minutes per session (median length, 35 minutes) during all shifts. A hand-hygiene opportunity16 was marked unsuccessful if the hand-hygiene practice observed did not comply with the NICU policy. Hospital occupational health services examined NICU personnel hands and reviewed health histories regarding potential P. aeruginosa colonization (eg, history of otitis externa). We also conducted audits of contact precautions and central-


line insertion and maintenance practices using standardized audit tools.17 We observed respiratory therapy, feeding practices, equipment reprocessing, pharmacy practices, envir- onmental cleaning, an eye exam, and routine patient care.


Environmental Evaluation


We performed environmental sampling in NICU patient areas with the strongest epidemiologic links to cases (ie, rooms with multiple cases or a recent case) on September 29, 2014. To collect samples, we removed POU filters from faucets and collected 1-liter water samples. POU filters were replaced after sampling. We also collected swab samples from faucets and drains and sponge-stick samples from sink basins. We collected additional sponge-stick and swab samples from ventilator equipment, breast pumps, an incubator humidity outlet, and shelves adjacent to the patient room sinks. We collected water samples from pipes delivering hot and cold water to the floor where the NICU was located. Samples were submitted to CDC for culture by membrane filtration of water and by homogenization and extraction of swabs and sponge sticks. Nonlactose fermenting, pigmented colonies that grew


on MacConkey selective agar were identified as P. aeruginosa using an automated biochemical identification system. To determine relatedness, pulsed-field gel electrophoresis


(PFGE) was performed at the CDC on 21 P. aeruginosa environmental isolates and 10 case isolates (5 surveillance and 5 clinical). We selected case isolates from the hospital laboratory that represented the most recent case patients or those with an epidemiologic link to environmental samples.


Risk Factors: Case-Control Study


To assess risk factors for positive P. aeruginosa culture, we conducted a case-control study. Surveillance and clinical cases were combined because the primary study focus was on assessing transmission risk factors. Control patients were deemed eligible if they (1) were admitted to theNICU between June 1, 2013, and September 30, 2014; (2) had a negative surveillance culture for P. aeruginosa; and (3) did not have any cultures positive for P. aeruginosa during the study period. We selected control patients randomly from an eligible patient list. Because case-patient birth weights were markedly lower than those of the general NICU population, we matched case patients 1:1 with a control patient according to the following birth weight categories: ≤1,000 g, 1,001–1,500 g, 1,501–2,500 g, and ≥2,501 g to ensure that control patients received similar exposures as case patients. The index date for controls was the most recent negative surveillance culture date. We abstracted data from electronic medical records using a


standard form that included the following data: demographics, maternal and obstetrical history, medical history and comor- bidities, medication and device exposure, nutrition, signs and


symptoms before positive culture, laboratory and microbiology findings, environmental exposure (ie, bed type and room number), exposure to NICU personnel, and clinical outcomes. We assessed exposures during the 7 days prior to positive cul- ture or the index date for all variables except antibiotic exposure, which we assessed during the 30 days prior to positive culture.


Statistical Analysis


We performed descriptive analyses of characteristics and exposures of case patients and control patients. We used conditional logistic regression adjusted for gestational age to evaluate the association between case status and each exposure. We reported exact odds ratios and 95% confidence intervals (CIs) due to limited sample size. We pooled matched sets according to the recommendations of Kleinbaum and Klein,18 resulting in models stratified by birth-weight category.


Ethical Review


The CDC National Center for Emerging and Zoonotic Infectious Diseases reviewed this investigation for human subjects’ protection and determined that it constituted an urgent public health response.


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