Introduction

Patients with major burns are, by definition, immunosuppressed, thus, there is a potential risk for acquiring a life-threatening infection [1]. Immune deficit due to the modulating effect of thermal injury includes impaired cytotoxic T lymphocyte response, impaired neutrophil function, decreased macrophage production, and neutropenia [2–4], making the burn patient especially vulnerable to infections.

Nosocomial infections are a significant problem in burn patients and bear clinical relevance. The reported incidence of nosocomial infections among burns patients varies at 63–240 per 100 patients and 53–93 per 1,000 patient days, depending mainly on the definitions used [5, 6]. Mortality due to nosocomial infections in burn patients is defined mostly by an advanced age, high percent TBSA, and having an underlying disease [7]. Besides increasing morbidity and mortality, nosocomial infections have significant economic consequences [8].

In patients with burns, infections arise from multiple sources; normal human skin is contaminated and colonized with microorganisms, and the moist, avascular burn eschar fosters microbial growth. Delays in surgical treatment have also been shown to increase invasive wound infections [7, 9].

Other sources of infections are common to other patients in intensive care units, including intravascular catheter-related infections and ventilator-associated pneumonia [10, 11], with an overall incidence of infection higher than that of other patients in intensive care units [6]. The role of the inanimate environment as a source of nosocomial infection is controversial [12]. However, there is evidence that especially burn units tend to be more contaminated than that of nonburn units [13]. The hospital bed and, particularly, mattresses and pillows, which are in direct contact with patients, pose a potential risk of infection for the patient if not adequately decontaminated [13, 14]. We sought to examine the bacterial cultures of the mattresses in burn center and the correlation between the bacterial cultures of the burn patients and their mattresses.

Patients and methods

The prospective study was conducted in the Helsinki Burn Centre, Department of Plastic Surgery, Helsinki, Finland, during 1 May 2009 to 31 January 2010. The study population consisted of adult patients with large burns requiring intensive care. Mattresses are special pressure-relieving mattresses. Samples were taken between the mattress cover and air cells. Three bacterial samples were taken during the course of treatment: the first sample before the beginning of the treatment, the second sample after 2-week treatment, and the last sample when the mattress was no longer needed, before laundry. The first sample also assessed the adequacy of cleaning methods between patients.

Results

We included 11 (nine men) burn patients, with a mean age of 51 years. Etiology of the burn injury was flame in ten patients. The total body surface area burned ranged from 8 to 70 %, summarized in Table 1.

Table 1 Demographic data of 11 burn patients
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The total number of samples was 28. In four cases, the cultivations were negative at every time point. In the first cultivation, seven were negative for bacteria.

The most common bacteria in mattress cultivations were Gram-positive bacteria, normally found on the skin Table 2. Bacillus cereus was found in two different mattresses, even though this bacterium was not found from the cultures taken from the corresponding patients.

Table 2 Distribution of microbes from mattresses determined by culture at three time points during the burn patient’s hospitalization
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There were individual bacterial findings such as Enterococcus faecium, Acinetobacter radioresistens, Staphylococcus haemolyticus, and Neisseria apatogenica. Of these findings, E. faecium and S. haemolyticus were also found in patients’ wound samples.

Discussion

In this study, the bacteria isolated from the mattresses of patients with burns were typical skin normal bacterial flora (coagulase-negative staphylococci and difteroids) or environmental (B. cereus) or bacteria of the GI canal (enterococci, micrococci, and Neisseria). In only 36 % of the cases the swabs from the mattresses were negative at every time point.

Our data shows that bacterial transfer from the patient to mattress is evident and in line with previous literature [14–16]. We also suppose, in the light of these present results, that translocation from the mattress to patient is possible. However, due to our study setting, two-week period between the first and second bacterial culture, it was not traceable. Further, it seems that mattresses can be carriers to other environmental bacteria. B. cereus, A. radioresistens, and N. apatogenica were found only in the mattresses.

Although infection is still the most frequent complication in thermal injuries, the number of patients dying of septicemia has decreased [1, 17]. Still, the burn wound sepsis remains an important infectious complication among burn victims. The outer surface of adult skin is colonized by a small number of microorganisms [18]. Thermal damage to the skin, resulting in the loss of the protective barrier, is an important step in the development of an infection. Nonpathogenic bacteria, belonging to normal human flora, may become pathogenic and, consequently, cause minor to life-threatening infections, especially in patients with immunosuppressed states, such as large burns [19].

Gram-negative bacteraemia, in contrast to Gram-positive bacteremia, is a significant predictor of mortality in burn patients [20]. Our results showed that Gram-negative bacteria were found growing in the mattresses, translocated from the patient’s wounds. Therefore, it is imperative that these pathogens problematic to burn patients should not be moved on to the next patient by the mattress.

Mattress contamination with various organisms, including MRSA, Pseudomonas aeruginosa, and Acinetobacter has been reported in a number of studies [14]. In the burn unit setting, wet mattresses served as an environmental reservoir of Acinetobacter [16]. Damaged mattresses have been found to be the source of contamination during outbreaks. During a pseudomonas outbreak in the burn unit, water-proof nylon-coated mattress cover was damaged by the silver nitrate solution, and pseudomonas survived in the foam under the cover [15]. It seems that mattresses are not considered as a potential source of nosocomial infections in the hospital. An audit of mattresses indicated that a large number of mattresses required replacement [21]. Cleaning and drying of the mattresses may remove organisms from the cover, while the inner wet foam may still contain bacteria that can leak out when a patient lies on the mattress [15], especially if the mattress is damaged. Perhaps, using biocidal textiles, especially in those textiles that are in close contact with the patients, might significantly reduce bioburden in clinical setting [22].

We conclude that the infection control program for burn centers requires strict compliance with a number of environmental control measures that include enforced hand washing and the use of personal protective equipment. Special pressure-relieving mattresses should be cleaned and disinfected according to manufacturer’s instructions. Damaged mattresses should be promptly replaced, and we recommend that, as a part of the infection control program, burn centers should monitor the decontamination of mattresses by sampling them after disinfections.