Elsevier

Burns

Volume 35, Issue 8, December 2009, Pages 1104-1111
Burns

Risk factors for acquisition of Methicillin-resistant Staphylococcus aureus among patients from a burn unit in Brazil

https://doi.org/10.1016/j.burns.2009.02.008Get rights and content

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is an important agent of colonization and infection in burn units. In order to identify risk factors for MRSA acquisition in a Brazilian burn unit, we performed two retrospective studies. In the first (“cohort” study), 175 patients who were not colonized with MRSA on admission were followed to assess risk factors for MRSA acquisition. In the second (“case–case–control” study), 143 individuals from the previous study who were negative for both MRSA and Methicillin-susceptible S. aureus (MSSA) on admission were followed. Case–control studies were performed to investigate risk factors for MRSA and MSSA acquisition. MRSA and MSSA were recovered from 75 and 23 patients, respectively. In the “cohort” study, only the number of wound excisions (Odds Ratio [OR] = 1.55, 95% Confidence Interval [CI] = 1.21–1.98, P = 0.001) was associated with MRSA acquisition. In the “case–case–control” study, burns involving head (OR = 3.43, 95%CI = 1.50–7.81, P = 0.003) and the number of wound excisions (OR = 1.83, 95%CI = 1.27–2.63, P = 0.001) were significant risk factors for MRSA. Burns involving perineum were negatively associated with MSSA acquisition (OR = 0.16, 95%CI = 0.03–0.75, P = 0.02). In conclusion, the acquisition of MRSA was related to the site of the burn and to the surgical manipulation of tissues, but not to the use of antimicrobials.

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) emerged as an important pathogen in burn units in the late 1970s [1]. Since then, there was an increasing report of MRSA outbreaks in those settings [2], [3], [4]. Also, this pathogen reached endemic levels worldwide [5], [6]. The relevance of MRSA colonization in burn patients is a matter of concern. Staphylococcal colonization may progress to infection, with a significant impact on morbidity and mortality [7]. It has been suggested that inpatients colonized with MRSA are more predisposed to infection development than those carrying Methicillin-susceptible S. aureus (MSSA) [8]. One study found that 14% of MRSA colonized burned patients developed bacteremia [1].

Early articles focused on risk factors for acquisition of MRSA [9], [10]. However, methodological issues limit the interpretation of their findings. Those issues have been emphasized in the literature: relying only in results from univariate analysis; inadequate control group selection; no adjustment for severity-of-illness or length of exposure to hospital environment [11], [12]; no assessment of colonization pressure [13].

The objective of our study was to assess risk factors for acquisition of MRSA in a burn unit in which this pathogen maintains hyperendemic levels. We tried to overcome biases by following the current methodological recommendations [11].

Section snippets

Settings

The study was conducted in Hospital Estadual Bauru (HEB), a 280-bed hospital in the city of Bauru, Brazil. It is one of the teaching hospitals from Faculdade de Medicina de Botucatu (Botucatu School of Medicine). The hospital has a burn unit with 16 beds. The unit comprises two wards: one for non-critical patients (12 beds, with single- and three-patients rooms) and one Intensive Care Unit (4 beds, single rooms). There is also an operating room for small procedures inside the burn unit. The

Incidence of MRSA and MSSA

During the study period, 199 patients were admitted to the burn unit. We excluded 22 patients from our studies for having MRSA recovered from cultures collected on the moment of admission to our hospital. Two other patients were excluded for not having any surveillance culture collected in the first 48 h of admission.

Seventy-five patients acquired MRSA during their stay in the burn unit. The incidence rate was 10.8 per 1000 patient-days. All patients harboring MRSA had positive surveillance

Discussion

Burn units have been recognized not only as wards with increased transmission of MRSA, but also as a reservoir for these bacteria, contributing to their dissemination all through the hospital [1]. However, few studies address specific factors that predispose burned patients to the acquisition of MRSA.

Some authors made assumptions about risk factors for MRSA acquisition on the basis of analysis of case series, often accompanied by molecular strain typing [4], [18], [19]. The lack of control

Conflict of interest

The authors of this manuscript state that there is no conflict of interest regarding the work that is being submitted.

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