Species Distribution and Susceptibilities of Bacteraemic Isolates from a United Kingdom Level 3 Neonatal Intensive Care Unit, a 5 Year Experience

Introduction

Survival rates amongst patients admitted to neonatal intensive care units (NICU) has increased significantly over the last ten years. One of the commonest interventions in patients admitted to NICUs is the initiation of antibiotics for the management of sepsis. Whilst there has been little change in the epidemiology of organisms associated with early onset sepsis (less than 72 hours), there has been increasing interest in the incidence and clinical relevance of coagulase negative staphylococci (CoNS). These organisms have the potential for pathogenicity in the neonates, the reasons for this include prematurity of the immune system, predisposing antibiotic consumption as well as the placement of intravascular catheters. The management of sepsis in NICUs is complex. There is a paucity of evidence based guidelines for the prescription of antimicrobials in children compared to the adult population, which results in a wide variation of guidelines between NICUs, often based on local experience and anecdotal evidence. Increasing levels of resistance in Gram negative organisms globally, as well as noticeable increases in the minimum inhibitory concentrations (MICs) of Gram positive organisms have specific implications in neonates. We aimed to look at isolates recovered from blood cultures, taken as part of routine clinical care to identify trends in resistance and map this to antimicrobial consumption in the unit over the last 5 years.

Methods

The NICU contains 6 intensive care cots and 6 high dependency cots alongside 22 special care cots. On average 7000 deliveries are managed by the unit each year, of a total of 11,500 deliveries across the Trust.

The hospital pathology system was queried for all blood cultures (irrespective of significance) between January 2005 and October 2010. Susceptibilities of isolates were downloaded for all CoNS and the Gram negatives that were associated with clinical signs of sepsis. Antimicrobial susceptibilities, including Gram negative resistances, were measured by automated methods, using with Vitek 2 system (Biomerieux, France) and reported according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints.  Consumption data for antibiotics (in terms of vials) were obtained from the pharmacy department, and based on the number of vials delivered to the unit. Individual medical notes and drug charts were not reviewed, but each blood sample was taken on clinical suspicion of sepsis, as per unit protocol. Data was analysed using Microsoft® Excel 2010 pivot tables.

Results

From January 2005 to October 2010, there were 794 positive blood cultures, of which 639 (80.5%) were identified as CoNS by routine laboratory methods. The remaining 155 included 34 (4.3%) other Gram positives (4 Staphylococcus aureus, 10 Streptococcus agalactiae and 20 alpha haemolytic streptococci) and 121 (16.5%) Gram negative organisms (120 Enterobacteriaceae and one Pseudomonas aeruginosa). Susceptibilities for Enterobacteraciae were unchanged over the study period, although a reduction in ampicillin resistance was noted. The susceptibilities that were analysed for CoNS were cloxacillin (CLX), ciprofloxacin (CIP), erythromycin (ERY), fusidic acid (FUS) and trimethoprim (TM). Best fit analyses were also plotted on the same graph (Fig 1). Vancomycin MICs were not performed routinely in the laboratory. Consumption data was generated from dispensary records in the pharmacy. Numbers of vials on each antibiotic was plotted (Fig 2). There are no WHO definitions for the defined daily dose (DDD)of antibiotics in neonates, and thus the numbers of vials was used as a rough guide of consumption data The 2011 consumption data in figure 2 only includes the first eight months of that calendar year.

Figure 1: Resistance Patterns amongst Coagulase Negative Staphylococci 2005-2010. Key: CLX=Cloxacillin, CIP=Ciprofloxacin, ERY=Erythromycin; FUS=Fusidic Acid; TM=Trimethoprim

Figure 2: Consumption of Antibiotic Vials in NICU 2005-2010