A longitudinal study of Acinetobacter in three Australian hospitals

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Summary

Acinetobacter has recently risen in prominence as a nosocomial pathogen, particularly due to increasing antibiotic resistance. The aim of this study was to describe changes in rates and antibiotic susceptibility patterns of Acinetobacter in three Melbourne hospitals. This was a retrospective review of microbiology records over five years. The rates of new clinical isolates of Acinetobacter per 10 000 discharges per quarter were calculated. Other information collected included antibiotic susceptibility patterns, age, gender, length of stay and ward [intensive care unit (ICU) or non-ICU]. Rates increased substantially at two hospitals, but not at the third. Increasing numbers at one hospital were associated with antibiotic resistance. Most first isolates were identified while the patient was in the ICU. Many isolates were from respiratory specimens, although a significant proportion was from blood. This study documents the establishment of Acinetobacter as a nosocomial pathogen in two Melbourne hospitals and serves as a warning for the future.

Introduction

Once considered as a harmless opportunist, Acinetobacter has recently risen to prominence as a multi-resistant nosocomial pathogen, prompting some to warn of the ‘return of the pre-antibiotic era’.1 Increasing antibiotic resistance has been reported in epidemic and endemic settings, necessitating the use of colistin, an antibiotic previously abandoned because of toxicity.1, 2, 3 Infection and colonisation with Acinetobacter baumannii have been associated with increased attributable mortality and prolonged hospital stay.3, 4

Numerous Acinetobacter outbreaks, many involving multi-resistant organisms, have been documented in Australia and elsewhere, including one reporting the emergence of carbapenem resistance in blood culture isolates at the Alfred Hospital in Melbourne.4, 5, 6, 7, 8 Others have reported clonal isolates of multi-resistant Acinetobacter baumannii present simultaneously in multiple hospitals in one geographical area over different periods of time.1, 9 There are no previous multicentre longitudinal epidemiological studies published from Australia. In this report, we describe the changing rates of Acinetobacter over a four-to-five year period at three major Melbourne teaching hospitals. We also describe some features of the affected patients.

Section snippets

Setting

This study was carried out at three tertiary referral hospitals in Melbourne, the Royal Melbourne Hospital (RMH), Monash Medical Centre (MMC) and the Alfred Hospital (AH). The RMH has approximately 350 beds [with 24 intensive care unit (ICU) beds], MMC has 637 (13 ICU beds) and AH has 350 (32 ICU beds). All provide adult medical and surgical services including cardiothoracic surgery, neurosurgery and renal transplantation. AH and RMH are the statewide providers of trauma services. AH also has

Results

A description of the study patients at each hospital is given in Table I. The mean and median length of stay at AH was longer than at the other two hospitals. A greater proportion of patients at RMH and AH had more than one ICU stay than at MMC. Rates per 10 000 discharges per quarter (whole hospital) are shown in Figure 1a. The peak rate per 10 000 discharges per month at RMH, MMC and AH respectively were 39.3 (October 2004), 21.1 (January 2000) and 49.6 (December 2003) (not shown). The number

Discussion

This study has shown three different distributions of Acinetobacter in three of the major tertiary institutions in Melbourne. At RMH, rates increased from March 2004, but with little antibiotic resistance. At MMC, rates did not change substantially over the five years and there was little antibiotic resistance. At AH, rates significantly increased with a marked increase in antibiotic resistance. Numbers did, however, decrease in 2005 at both RMH and AH (data not shown). Although we did not

Acknowledgements

We gratefully acknowledge the following people for their help in data extraction and statistical advice. RMH: D. Giltrap, M. Anderson, P. Barfett, L. MacGregor; MMC: D. Kotsanas, A. Gosden; AH: A. LaSala, P. Pham.

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