Bacteriology
First identification of methicillin-resistant Staphylococcus aureus MLST types ST5 and ST45 and SCCmec types IV and Vt by multiplex PCR during an outbreak in a respiratory care ward in central Taiwan,☆☆,

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Abstract

We used molecular typing methods to investigate an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) infections in a respiratory care ward in Taiwan. From March to June 2006, the incidence of MRSA infection increased 3.75-fold. The overall carrier rates among the health care workers (HCWs) were 31.3% (total S. aureus), 16.4% (MRSA), and 14.9% (methicillin-sensitive SA, MSSA). Pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), antibiograms derived from susceptibility testing of MRSA isolates, and multiplex polymerase chain reaction (PCR) provided strong epidemiologic and microbiologic evidence that the outbreak of MRSA infections at our hospital was linked to the same PFGE pulsotype A SCCmec type II, pvl-negative, MLST ST5 strain of MRSA isolated from seven HCWs and five patients. The outbreak was controlled by application of topical fucidin ointment to the anterior nares in all colonized HCWs. Multiplex PCR combined with PFGE and MLST is a feasible method for outbreak investigations in routine clinical laboratories.

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) is a worldwide problem with significant prevalence in Asia. In a study conducted in Taiwan, the prevalence of MRSA among isolates of S. aureus was reported to have increased from 39% in 1991 to 75% in 2003, with the increase attributed to the overuse of certain antibiotics (Hsueh et al., 2005).

Health care-associated MRSA (HA-MRSA) infection appears to be less common in respiratory care wards (RCWs) in Taiwan (Kuo et al., 2008). However, the Nosocomial Infection Control Subcommittee of our hospital became aware of an outbreak occurrence in the RCW in May 2006 because of the increasing number of patients infected with MRSA between March and May 2006, and subsequently intervened during the outbreak in June 2006. From March to June 2006, MRSA was isolated from eight patients and an outbreak of MRSA infection was suspected. The aim of this study was to use the results of a variety of molecular typing techniques to characterize the strains isolated from health care workers (HCWs) and patients during this outbreak. In so doing, we evaluated the feasibility of these molecular methods for application during an outbreak investigation performed by a standard clinical laboratory.

Section snippets

Outbreak scenario

The Chung-Kang branch of the Chung Shan Medical University Hospital is a 169-bed general hospital. The outbreak of MRSA infection occurred only on one floor in an RCW that cared for patients hospitalized with chronic respiratory failure and those requiring a ventilator. At the time of this investigation, the ward housed 23 inpatients, five of whom had renal failure and were undergoing regular hemodialysis. These patients were cared for by 67 HCWs (including three attending physicians and two

Incidence of carriage and infection by MRSA

The index patient (Patient 1) was admitted on January 4, 2005, and developed a urinary tract infection, pneumonia, and septic shock on March 13, 2006. MRSA was isolated from two sets of blood cultures. Between April 14 and June 17, 2006, eight episodes of MRSA infection were confirmed. Five patients had primary MRSA bacteremia, one of whom had two episodes of bacteremia during a period of 3 weeks (Patient 4). Ultimately, nine isolates obtained from eight patients were confirmed to be MRSA

Discussion

The goals of our study were to characterize a single MRSA outbreak in our institution with methods that could differentiate between cases that were associated with the index case and those that were not and to validate these methods in our routine clinical setting. For this purpose, we chose a combination of PFGE, multiplex PCR to determine the SCCmec and pvl gene type, and MLST typing. Our results from PFGE, MLST typing, multiplex PCR, and antibiograms derived from susceptibility testing of

Acknowledgment

We thank both the Center for Research and Diagnostics and the Central Regional Laboratory of Taiwan CDC for PFGE genetic typing analysis of MRSA strains.

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    Previous presentation: This study was presented as an abstract at the 11th Western Pacific Congress on Chemotherapy and Infectious Diseases, Dec. 1, 2008, Taipei, Taiwan.

    ☆☆

    Funding and support: The study was supported by the Chung Shan Medical University Hospital Grant No. CSH-97-C-01.

    Conflict of interest: The authors declare that they have no conflict of interest.

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