The epidemiology of methicillin-resistant Staphylococcus aureus in a burn center

Bacterial colonisation of the burn wound: a UK experience

OBJECTIVE

Bacterial colonisation of the burn wound remains a major source of morbidity and mortality in burns patients. This study aimed to determine the presence of different micro-organisms in a UK regional burns centre and to examine the relationships between bacterial colonisation, burn size, length of hospital stay and delayed referral.

METHOD

A retrospective review of microbiology surveillance swab results on all adult patients admitted to a regional burns centre over a 12-month period was performed.

RESULTS

139 adult patients were included in the study. Approximately 68% of patients showed evidence of burn wound colonisation at some point during their inpatient stay. The remaining 32% had negative microbiology swabs throughout their hospital stay. A total of 202 micro-organisms were isolated. Staphylococcus aureus was found to be the most common micro-organism, found in 79% of patients with positive swab results. A direct link was found between an increased incidence of bacterial colonisation and delay in referral of >24 hours, larger burn size and length of hospital stay.

CONCLUSION

By understanding the potential sources of bacteria and the effect of patient factors on their susceptibility to bacterial colonisation, we can form better management and treatment strategies to reduce morbidity and mortality from burns wound sepsis.

The impact of the types of microorganisms isolated from blood and wounds on the results of treatment in burn patients with sepsis

Despite development of combustiology, infections continue to be the most important cause of death among patients with burns. Sepsis is the most severe clinical presentation of infection in patients after thermal injuries who require immediate treatment. Early diagnosis and proper treatment of sepsis are important in the clinical management that is often hampered for multiple reasons, e.g. impaired patient immunity, problems with microorganisms with multi-antibacterial drug resistance. The aim of the study was to assess effect of type of a microorganism isolated from blood and wound on results of treatment of sepsis in patients with burns.

MATERIAL AND METHODS

Effect of type of microorganisms isolated from blood and wound on the result of treatment of sepsis was studied in 338 patients hospitalized immediately after an injury in Centre for Burn Treatment in Siemianowice Śląskie in years 2003 - 2004 (at the age of 18 - 96 years, 66 women and 272 men). Clinical symptoms of generalized infection were found in all study subjects. The study group was divided into two subgroups: cured patients and patients who died of sepsis. The following parameters were assessed in both subgroups: type of microorganism isolated from blood, type of microorganism isolated from wound as well as occurrence of the same and different infections of blood and burn wound.

RESULTS

positive blood cultures were found in 165 patients (48.8%), 106 (64.2%) were cured, 59 (35.8%) died. The most commonly isolated microorganisms in cured patients were Gram(+) Staphylococcus epidermidis MRSE (19.81%) and Staphylococcus aureus MRSA (18.87%). Gram(-) intestinal rods were least commonly isolated from this group. The most commonly isolated microorganisms from blood of patients who were to die, included non-fermenting Gram(-) rods Acinetobacter baumannii (35.59%) and Pseudomonas aeruginosa (22.03%). Mixed bacterial flora was found in the blood of 22.03% patients. Among patients who were to die, the same microorganisms were found in the blood and in the wound in 32.2% of patients, while this rate was 17.92 in cured patients. The most commonly found bacteria in the blood and burn wound in the cured patients included Staphylococcus aureus MRSA (31.58%) and Staphylococcus aureus (21.05%). In the group of patients who were to die, the most common bacteria isolated simultaneously from the blood and burn wound included Acinetobacter baumannii (47.37%) and Pseudomonas aeruginosa (36.84%).

CONCLUSIONS

1. The patients with thermal injuries are at higher risk of death in the event of sepsis caused by Gram(-) bacteria versus Gram(+) bacteria. 2. Infection of blood and burn wound caused by the same bacteria Pseudomonas aeruginosa and Acinetobacter baumanni increases the risk of death due to sepsis in patients with burns following thermal injuries.

Enhancement of neutrophil function by interleukin-18 therapy protects burn-injured mice from methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) infection is a grave concern in burn-injured patients. We investigated the efficacy of interleukin-18 (IL-18) treatment in postburn MRSA infection. Alternate-day injections of IL-18 into burn-injured C57BL/6 mice significantly increased their survival after MRSA infection and after methicillin-sensitive S. aureus infection. Although IL-18 treatment of burn-injured mice augmented natural IgM production before MRSA infection and gamma interferon (IFN-γ) production after MRSA infection, neither IgM nor IFN-γ significantly contributed to the improvement in mouse survival. IL-18 treatment increased/restored the serum tumor necrosis factor (TNF), IL-17, IL-23, granulocyte colony-stimulating factor (G-CSF), and macrophage inflammatory protein (MIP-2) levels, as well as the neutrophil count, after MRSA infection of burn-injured mice; it also improved impaired neutrophil functions, phagocytic activity, production of reactive oxygen species, and MRSA-killing activity. However, IL-18 treatment was ineffective against MRSA infection in both burn- and sham-injured neutropenic mice. Enhancement of neutrophil functions by IL-18 was also observed in vitro. Furthermore, when neutrophils from IL-18-treated burn-injured mice were adoptively transferred into nontreated burn-injured mice 2 days after MRSA challenge, survival of the recipient mice increased. NOD-SCID mice that have functionally intact neutrophils and macrophages (but not T, B, or NK cells) were substantially resistant to MRSA infection. IL-18 treatment increased the survival of NOD-SCID mice after burn injury and MRSA infection. An adoptive transfer of neutrophils using NOD-SCID mice also showed a beneficial effect of IL-18-activated neutrophils, similar to that seen in C57BL/6 mice. Thus, although neutrophil functions were impaired in burn-injured mice, IL-18 therapy markedly activated neutrophil functions, thereby increasing survival from postburn MRSA infection.

Pathogenic role of macrophages in intradermal infection of methicillin-resistant Staphylococcus aureus in thermally injured mice

Intradermal infection of methicillin-resistant Staphylococcus aureus (MRSA) in burned mice was pathogenically analyzed. An abscess was formed in normal mice intradermally infected with 10(8) CFU/mouse of MRSA, and all of these mice survived after the infection; however, abscess formation was not demonstrated to occur in burned mice similarly exposed to the pathogen, and all of these mice died within 5 days of infection. In burned mice, MRSA infected at the burn site intradermal tissues spread quickly throughout the whole body, while in normal mice, the pathogen remained localized at the infection site. Macrophages (Mφ) isolated from the infection site tissues of normal mice produced interleukin-12 (IL-12) but not IL-10 and were characterized as M1Mφ. These M1Mφ were not isolated from the infection site tissues of burned mice. When normal-mouse infection site tissue Mφ were adoptively transferred to burned mice at the MRSA infection site, an abscess formed, and the infection did not develop into sepsis. In contrast, an abscess did not form and sepsis developed in normal mice that were inoculated with burned-mouse infection site tissue Mφ. These Mφ produced IL-10 but not IL-12 and were characterized as M2Mφ. These results indicate that abscess formation is a major mechanism of host resistance against intradermal MRSA infection. M1Mφ in the tissues surrounding the infection site play a pivotal role in abscess formation; however, the abscess is not formed in burned mice where M2Mφ predominate. M2Mφ have been described as inhibitor cells for Mφ conversion from resident Mφ to M1Mφ.

Methicillin-resistant Staphylococcus aureus transmission: the possible importance of unrecognized health care worker carriage

BACKGROUND

This study was conducted to evaluate the ongoing transmission of methicillin-resistant Staphylococcus aureus (MRSA) in a 10-bed trauma intensive care unit (TICU) in a large teaching hospital.

METHODS

Surveillance cultures for MRSA were obtained on admission to the TICU. Colonized or infected patients were placed on contact precautions. On February 21, 2003, 19 burn patients were admitted to the TICU after a local mass casualty event. Universal barrier precautions were implemented for all patients, and point-prevalence surveys (nares cultures) were used to detect MRSA acquisition.

RESULTS

During March 2003, 58% of the burn patients developed MRSA infection or colonization. Six of 133 health care workers (HCWs) had positive MRSA screening cultures. Seven patients and 4 HCWs harbored the pulsed-field gel electrophoresis clone A. Two patients and 1 HCW harbored clone B. Once the colonized HCWs were successfully decolonized, a sustained reduction in MRSA infections occurred.

CONCLUSION

Transmission of MRSA in an ICU was observed despite various infection control precautions. Identifying and treating colonized HCWs was followed by a significant reduction in the incidence of MRSA. Unrecognized MRSA-colonized HCWs may be an important reservoir in endemic institutions that could impair other control measures.

Immunological control of methicillin-resistant Staphylococcus aureus (MRSA) infection in an immunodeficient murine model of thermal injuries

Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), is a major cause of sepsis in patients who are immunosuppressed by their burns. In this study, an immunological regulation of MRSA infection was attempted in a mouse model of thermal injury. SCIDbg mice were resistant to MRSA infection, while SCIDbgMN mice (SCIDbg mice depleted of neutrophils and macrophages (Mphi)) were susceptible to the same infection. Also, thermally injured SCIDbg mice were shown to be susceptible to MRSA infection. On the other hand, the resistance of SCIDbgMN mice to the infection was completely recovered after an inoculation with Mphi from normal mice. However, anti-MRSA resistance was not shown in SCIDbgMN mice inoculated with Mphi from thermally injured mice. Mphi from MRSA-infected thermally injured mice were identified as alternatively activated Mphi, and Mphi from MRSA-infected unburned mice were characterized as classically activated Mphi. Mphi from thermally injured SCIDbg mice previously treated with 2-carboxyethylgermanium sesquioxide (Ge-132) protected SCIDbgMN mice against MRSA infection. Ge-132 has been described as an inhibitor of alternatively activated Mphi generation. These results suggest that MRSA infection in thermally injured patients is controlled immunologically through the induction of anti-MRSA effector cells and elimination of burn-associated alternatively activated Mphi, which are cells that inhibit the generation of classically activated Mphi.

Infections in a burn intensive care unit: experience of seven years

The objective of this study is to describe infections in a specialized burns intensive care unit from 1993 to 1999. The criteria for admission to the unit are: children with burns involving at least 10% or adults with burns involving at least 20% of total body surface; burns affecting face, perineum or feet; suspected or proven airway injury; electric or chemical burns; age less than one year or above 50; or pre-existing disease with any extent of burns. Surveillance of hospital-acquired infection was prospective. Hospital-acquired infection criteria used were those modified from the Centers for Disease Control and Prevention. Diagnosis of infection using skin biopsy was not done. Over the study period, 320 patients were admitted to our burns intensive care unit. One hundred and seventy-five (55%) developed 388 hospital-acquired infections. The rate for vascular catheter-associated bloodstream infections was 34 per 1,000 central line-days. The rate of ventilator associated pneumonia was 26 infections per 1,000 ventilator-days. Primary bloodstream was the most common infection with 189 episodes (49%); followed by 83 burn wound infections (21%) and 56 pneumonias (14%). In 76% of these infections and in 97% of the primary bloodstream infections, aetiological agents were identified. The micro-organisms causing infections were S taphylococcus aureus (24%), Pseudomonas aeruginosa (18%), Acinetobacter spp. (14%) and coagulase-negative staphylococci (12%). Candida spp. caused 8% of infections. Gram-positive and Gram-negative organisms exhibited resistance to most antimicrobial agents used for therapy. During the first three days of hospitalization in the burns intensive care unit there were eight infections caused by S. aureus and three of these were resistant to oxacillin. These data provide background information regarding extensive burn patients on which decisions for control and prevention of hospital-acquired infections can be made.

Septicaemia after burn injury: a comparative study

Seventy-nine (8.4%) patients during June 1992-May 1996 (Group-1) and 68 (7.2%) patients from June 1996 to May 2000 (Group-2) who developed septicaemia at the burns unit of Al-Babtain Centre for Plastic Surgery and Burns, Kuwait, were retrospectively studied and compared. The mean age of 26 years, male predominance, flame burns as main aetiology and mean burn percentage of >or=40% was observed in both the groups. Both groups revealed extensive flame burn, inhalation injury, intubation and difficult resuscitation as the risk factors. The proportion of satisfactory resuscitation increased significantly (P<0.001) in Group-2. The septicaemia commonly occurred within 2 weeks postburn but the number of episodes during 5 days postburn was less in Group-2. The surface wound was found to be the likely source of entry of the organisms into the blood stream in both the groups. The gram positive organisms were dominant aetiologic factor in both groups but an increase frequency of Acnetobacter was found in Group-2. The proportion of MRSE and Pseudomonas septicaemia was significantly higher (P<0.01) in the Group-1. The rate of survivors, in both the groups was higher among operated patients but it was significantly higher (P<0.001) in the Group-1. A mortality rate 20.6% in Group-2 decreased against Group-1, which can be attributed to better resuscitation, nutritional care, early detection of septicaemia, appropriate antibiotics and early wound excision and skin grafting. MOF was the cause of death of 60.9% in Group-1 and 85.7% in Group-2. There was no role of prophylactic antibiotic in burn patients in the incidence of septicaemia and mortality.

An outbreak of methicillin resistant Staphylococcus aureus on a burn unit: potential role of contaminated hydrotherapy equipment

OBJECTIVE

To report a multi-institution outbreak caused by a single strain of methicillin-resistant Staphylococcus aureus (MRSA).

OUTBREAK

Between September 19 and November 20, 1996 an index case and five secondary cases of nosocomial MRSA occurred on a 26 bed adult plastic surgery/burn unit (PSBU) at a tertiary care teaching hospital. Between November 11 and December 23, 1996, six additional cases were identified at a community hospital. One of the community hospital cases was transferred from the PSBU. All strains were identical by pulsed-field gel electrophoresis. MRSA may have contributed to skin graft breakdown in one case, and delayed wound healing in others. Patients required 2 to 226 isolation days.

CONTROL MEASURES

A hand held shower and stretcher for showering in the hydrotherapy room of the PSBU were culture positive for the outbreak strain, and the presumed means of transmission. Replacement of stretcher showering with bedside sterile burn wound compresses terminated the outbreak. The PSBU was closed to new admissions and transfers out for 11 days during the investigation. Seven of 12 patients had effective decolonization therapy.

CONCLUSION

Environmental contamination is a potential source of nosocomial MRSA transmission on a burn unit. Notification among institutions and community care providers of shared patients infected or colonized with an antimicrobial resistant microorganism is necessary.

Staphylococcal septicaemia in burns

This study analyses staphylococcal septicaemia in a series of 1516 burn patients who were admitted to the burn unit of the Al-Babtain Centre for Burns and Plastic Surgery, Ibn Sina Hospital, Kuwait over a period of 6.5 years (1 June 1992-31 December 1998). One hundred and nine patients (7.2%) developed clinically and microbiologically proven septicaemia, of which 80 (73.4%) showed one or the other type of Staphylococcus in their blood. Fifty (62.5%) of them were males and 30 (37.5%) females, with a mean age of 26 years and the mean total body surface area of burns (TBSA) of 45% (range 1-93%). Preschool age children comprised 27.5% of the patients. Flame was the dominant (80%) cause of burn. Of the 80 patients who had 91 episodes of septicaemia, 52 (65%) had MRSA, 8 (10%) MSSA, 11 (13.8%) MRSE and 5 (6.2%) MSSE and 4 (5%) others had mixed organisms. Only the patients with MRSA had multiple episodes. Eight patients (10%) showed septicaemic episodes within only 48 h of admission; however, the majority of the patients (77.5%) had a septicaemic attack within 2 weeks postburn. Of the 52 MRSA septicaemic cases, 39 (75%) survived and 13 (25%) died. Four patients with septicaemia due to mixed infections died. A total of 19 patients were intubated, 14 due to inhalation injury and 5 because of septicaemia; all in the former group died. Glycopeptide therapy (vancomycin/teicoplanin) was instituted immediately following the detection of staphylococci in the blood. No significant difference was noted in relation to mortality amongst the septicaemic patients, whether or not on prophylactic antibiotic. Fifty-six (70%) of the 80 patients had 139 sessions of skin grafting and survived. Of the 52 MRSA patients, 40 had 101 sessions of skin grafting and 33 of them survived. The apparent low mortality was probably due to early detection of the organism, appropriate antibiotic therapy, care for nutrition and early wound cover. This study indicates a high incidence of staphylococcal septicaemia (especially due to MRSA) in the burn unit. A surface wound is the likely source of entry to the blood stream in these immunocompromised patients. The organism could be detected in blood as early as 48 h postburn and in as little TBSA burn as 1% in this MRSA endemic unit. Inhalation injury with major burns and added staphylococcal septicaemia invariably proved to be fatal.

A profile of methicillin resistant Staphylococcus aureus infection in the burn center of the Sultanate of Oman

A retrospective study of patterns of infection in 168 patients admitted during 1995 and 1996 in the burns-unit of Khoula hospital at Muscat, Oman was performed. Out of 819 isolates positive for pathogenic bacterial culture, there were 326 (39.8%) isolates positive for methicillin resistant Staphylococcus aureus (MRSA) infection. Incidence of MRSA infection was marginally more than that of Pseudomonas aeroginosa. The proportion of patients developing MRSA infection sometime or the other during their burns-unit stay ranging from 1 to 112 days rose from 48% in 1995 to 52.7% in 1996. No sophisticated tests were done to identify the MRSA strain but study of the antibiograms of each MRSA positive isolate showed very similar patterns of sensitivity to different antibiotics. This suggests the source of infection to be common and in all probability 'noscomial', since all patients acquired MRSA infection in the hospital. The susceptibility of MRSA to ciprofloxacin, cotrimoxazole and fucidin was 76, 51 and 37% of isolates in 1995, and 59, 44 and 26% in 1996 were susceptible to these drugs. Vancomycin was the antibiotic to which most MRSA cultures were susceptible, but partial resistance was reported due to very low susceptibility observed in 1.4% of the isolates in 1995 and 1.1% of the isolates in 1996. The control measures being practiced in the burns-unit of Khoula Hospital, especially mechanical cleaning and chemical disinfection of all surfaces, are discussed in detail. This paper emphasizes the need for preventive measures against MRSA infection in the burns-unit.

Burn septicaemia: an analysis of 79 patients

Out of 943 patients treated from June 92 to May 96 at the burns unit of the Al-Babtain Centre for Plastic Surgery and Burns, Kuwait, 280 (30%) required admission to the burns intensive care unit (ICBU) and were studied retrospectively. Seventy-nine (28.2%) developed clinically and microbiologically proven septicaemia. Forty-four (56%) were males, 35 (44%) females with a mean age of 26 years (range 45 days to 75 years) and mean total body surface area burn (TBSA) of 46% (range 10-90%). Sixty-two had flame burns, 16 a scald and one had an electric burn. These 79 patients had a total of 118 septicaemic episodes. Sixty (76%) had only one and 19 (24%) had multiple episodes of septicaemia. Fifty-four (68%) had their first episode within 2weeks, though the maximum number of episodes was between 6 and 10 days postburn. Septicaemia was also observed in 13% of patients within 3 days postburn. Out of the 118 episodes, 48 were due to methicillin resistant Staphylococcus aureus (MRSA), 17 due to methicillin resistant Staphylococcus epidemidis (MRSE), 15 to Pseudomonas, 12 to Acinetobacter, four to Streptococcus, another four to Enterococci, two to Klebsiella, one due to Serratia and 15 to more than one organism. Once the septicaemia was diagnosed appropriate therapy was instituted. Fifty-six (71%) patients had 143 sessions of skin grafting and the mortality was low in operated patients. Twenty-three (29.1%) patients died. The low mortality rate was probably due to factors such as continuous clinical and microbiological surveillance leading to quick detection of aetiology, appropriate antibiotic therapy, care for nutrition and early wound cover. This study suggests that flame burn patients are more vulnerable to sepsis. Onset of septicaemia may be as early as 3 days and commonly within 2 weeks. A surface wound is the likely source of entry to the blood stream. Gram positive organisms are dominant in the aetiology. Early detection and appropriate treatment including wound coverage result in a better outcome.

The use of porphyrins for eradication of Staphylococcus aureus in burn wound infections

The assessment of deuteroporphyrin-hemin complex as an agent for the treatment of burn wounds infected with a multiple-drug resistant strain of Staphylococcus aureus was performed. The effect of the porphyrin on the survival of the infectious bacteria was first assayed in culture, and later tested as well in a burned infected animal model. The addition of deuteroporphyrin and hemin, separately or together (as a complex) to a growing culture of S. aureus was monitored during 8 hours. It was found that deuteroporphyrin alone was strongly bactericidal only after photosensitization. On the other hand, hemin alone was moderately bactericidal but light independent. A combination of both deuteroporphyrin and hemin was extremely potent even in the dark and did not require illumination to eradicate the bacteria. The in vivo experiments by application of the above porphyrins in combination to infected burn wounds in guinea pigs was an effective way to reduce dramatically the contaminating S. aureus. Reduction of more than 99% of the viable bacteria was noted after the porphyrin mixture was dropped on the eschar or injected into the eschar, an effect that lasted for up to 24 hours. The deuteroporphyrin-hemin complex may be suggested as a new bactericidal treatment of S. aureus infected burns since it was found to be a potent and promising anti-Staphylococcal agent.

Effective control of methicillin-resistant Staphylococcus aureus in a burn unit

Methicillin-resistant Staph, aureus (MRSA) colonization and infection was studied in 231 patients who were admitted to our burn unit and remained for 3 days or more between 1986 and 1994 (patients with inhalation injury only and no burn wound were excluded). The study was divided into two periods: from 1988 to 1989 and from 1990 to 1994. MRSA was found in 80 patients. They increased from 1986 to 1988, slightly decreasing thereafter. In 1994 the incidence of MRSA was 4.3 per cent. The number of strains of MRSA isolated from burn wounds was significantly reduced in the later period. Comparing the two periods, isolation of patients from MRSA, prevention of contamination during care, and reduction in the number of patients initially given second- or third-generation cephem antibiotics were performed more strictly in the later period. The effectiveness of these measures was confirmed. Moreover, the first operation was carried out significantly earlier in the later period. Early excision and early closure of the wound was more effective in preventing and controlling MRSA colonization and infection.

Control of methicillin-resistant Staphylococcus aureus in a pediatric burn unit

BACKGROUND

Control of methicillin-resistant Staphylococcus aureus (MRSA) is particularly difficult in burn units, which are often cited as sources of hospital-wide MRSA outbreaks. We developed a successful MRSA control program and document here its apparent effectiveness in controlling MRSA transmission in a pediatric burn unit.

METHODS

An MRSA control program that included surveillance culturing, clinician feedback, flexible, site-specific isolation, and a list of known carriers was consistently applied in a pediatric burn unit through a 7-year period. Microbiology reports of MRSA isolates from patients and environmental surfaces and records of all patients from whom MRSA was isolated were reviewed.

RESULTS

During calendar years 1985 through 1991, a total of 991 acutely burned children were admitted to the Boston unit of the Shriners Burns Institute. Forty MRSA cases (4%) were identified. One patient both had MRSA at admission and met our criteria for nosocomial MRSA. Of the remaining 39 patients, 11 had MRSA at admission and 28 had nosocomial MRSA. There were 17 wound infections, two cases of pneumonia, and two bloodstream infections. No deaths were attributed to MRSA sepsis.

CONCLUSION

An MRSA control program including surveillance culturing, clinician feedback, flexible, site-specific isolation, and a list of known carriers is associated with a low rate of nosocomial MRSA in a pediatric burn unit.

Infection control in a Third World burn facility

A study of wound colonization by bacteria in 49 consecutive admissions was conducted over a 2-month period in patients with burns at King Edward VIII and Clairwood Hospitals, Durban, neither of which possess proper burn units. Specimens for culture were collected from patients, staff and the environment. Bacteria most frequently isolated were Staph. aureus, Klebsiella spp., Ps. aeruginosa and Enterobacter spp. Cross-infection occurred due to breakdown of aseptic techniques. Staff hands and contaminated baths and benches were also implicated. Recommendations to reduce cross-infection are presented.