Microbiological surveillance of burn unit of EPM / UNIFESP in São Paulo , Brazil Perfil microbiológico da unidade de queimaduras da EPM / UNIFESP , São Paulo , Brasil

1 MD, Phd Professor Of Plastic Surgery Division Of EPM/UNIFESP. 2 MD, Phd Assistant Of Infectology Division Of EPM/UNIFESP. 3 MD, Fellow Master Degree Infectology Post Graduate Program, EPM/UNIFESP. 4 Medical Student Of EPM/UNIFESP Medical Student Of EPM/UNIFESP. 5 Nurse, Fellow Master Degree Plastic Surgery Post Graduate Program, EPM/UNIFESP. 6 MD, Phd Head Of Central Laboratory Of São Paulo Hospital. 7 MD, Phd Chairwoman, Full Professor Of Plastic Surgery Division Of EPM/UNIFESP, São Paulo/São Paulo/Brazil. ABSTRACT Introduction: Despite great advances in treatment, burned skin infection remains a major challenge. The aim of this study is to evaluate the microbiological aspects of the first year’s operation of a Burn Unit in a University Hospital. Methods: Retrospective study. Microbiological data were collected and analyzed from patients admitted to the Burn Unit of São Paulo Hospital, a University Hospital of the Paulista Medical School (EPM) of the Federal University of São Paulo (UNIFESP) from June 2009 to July 2010. Results: The average length of stay was 13.8 days with a mortality rate of 5.9%, and median of TBSA was 10.3%. Evaluated 159 cultures from 101 patients. Blood cultures were the most requested (41%). It was also accessed 245 surveillance cultures collected from 75 patients. The microbiological analysis revealed a total positivity rate of 34,5%. The most prevalent agents were Coagulase-negative Staphylococcus CoNS (33%), Pseudomonas aeruginosa (24%), Acinetobacter spp. (22%) and Klebsiella pneumoniae (5%). Conclusion: The microbiological evaluation of the first year’s activity of EPM/UNIFESP Burn Care Unit revealed that, although the most prevalent agent was CoNS, Gram negative bacilli are still very prevalent, such as Pseudomonas aeruginosa and Acinetobacter baumannii. Despite the short time of operation, was observed large number of multiresistant microorganisms which can be explained by long exposure to antimicrobials and high transfer rate from other hospitals.


INTRODUCTION
Infections are major causes of mortality in severely burned patients.The United States has the highest mortality rates in patient's victims of burns among industrialized countries 1 .In Brazil, burns are responsible for over than 100.000hospital admissions and 2.500 deaths per year 2 .Burn treatment is funded by the government and needs of epidemiological data for the correct management and publishing for prevention 3 .
This patients are most susceptible to developing infection, as changes occur in the immune system due to dysfunction of granulocytes, reduced numbers of circulating lymphocytes and reduction of substances such as IL-2 and IgG.The largest burn extension, the higher probability of the patient developing infection.
Studies evaluating the frequency of infections in these patients show that bloodstream infections, respiratory tract infections, urinary tract infections and skin infections are most prevalent 4 .
Despite great advances in treatment, burned skin infection remains a major challenge.The disruption in skin barrier, vascular changes in the tissue and immune system dysfunction contribute to infection.In addition, the wound environment is propitious to microorganism's development 4 .
The aim of this study is to evaluate the microbiological aspects of the first year's operation of a burn unit in a University Hospital.

METHODS
This is are trospective epidemiological study where we evaluated the microbiological data from patients admitted to the burn unit of SãoPaulo Hospital, a University Hospital of the Paulista Medical School (EPM) of the Federal University of São Paulo (UNIFESP) from June2009 to July 2010.
Thisstudy was approved by the Research Ethics Committee of EPM/UNIFESP under number 1272/10.
Opened in June 2009, the Burn Unit of São Paulo Hospital is a high complexity center with four intensive care and six ward beds and operative room in the Burn Unit.São Paulo Hospital is a University Hospital that belongs to the Paulista Medical School of the Federal University of São Paulo.
Evaluated 159 cultures from 101 patients admitted to the Burn Unit from July 2009 to June 2010.
The microbiological protocol of patient care in the burn unit is started by collecting samples from the wound, oropharyns and rectum at the patient's arrival in the burn unit.During the clinical outcome when the patient has systemic symptoms such as fever, abnormal white blood cell count, increase of PCR and other inflammatory markers, or local changes, such as discoloration of the wound, the presence of cellulitis or vasculitis, is collected culture of the wound and blood culture.When there are specific signs such as changes in the urinary, digestive, pulmonary systems, most common sources of infection, among several, specific cultures are required for diagnosis.
Microbiological data were analyzed considering the culture requested, prevalent agents and antimicrobial susceptibility.All cultures were processed at Microbiology Central Laboratory from São Paulo Hospital.The microorganism identification and susceptibility tests for antimicrobial drugs were processed by automated system (Phoenix -BD®).The interpretative criteria's for break points definition to the susceptibility followed the CLSI standards (Clinical Laboratory Standards Institute) document M100-S19.
Patient and burn's characteristics such sex, age, total body surface area (TBSA), surgical procedures, injury severity were also evaluated by epidemiologic form filled out during patient's hospitalization.

Clinical features assessed considered average hospital stay between admission and surgery, burn infection and graft lost.
Burn infection is defined by the invasion of microorganisms in the area of the burn injury with the presence of signs such as discoloration, from points of vasculitis, points or plaques blackened in the subcutaneous tissue, presence of cellulitis around the lesion, secretion on the lesions and systemic repercussions with abnormal laboratory tests.Graft skin loss is when the skin does not take by the presence of exudate or other serous solution between the graft and the recipient site.This can occur by local conditions of the recipient site or the systemic conditions of the patient, more often as a septic shock.
Statistical analysisof results was obtainedby SPSS software.

RESULTS
From June 2009 to July 2010, 101 patients were admitted at the Burn Unit.During this period an epidemiological study was performed and revealed that the average age of patients admitted was 33.7 years and they were male in 66.7% of admissions 3 .
The average length of stay was 13.8 days with a mortality rate of 5.9%.The median of TBSA was 10.3% and 64.3% were regarded as small burns (Table 1).The mean time to surgery (debridement or grafting) was 4.4 days.
During the studied period, the average of surgeries per month was 9.1.Debridement and skin grafting, in distinct surgical moments, were the most common procedures, respectively 39 (35.4%) and 37 (33.6%)(Table 2).
It was also accessed 245 surveillance cultures collected from 75 patients with distribution of site collection and isolated microorganisms (Figures 2 and 3).
When it was evaluated the surveillance cultures, it was found a prevalence of Coagulase Negative Staphylococcus, Escherichia coli and Staphylococcus aureus.
Among Gram positives, was founded 26% and 5% of resistance to oxacilin in CoNS and S. aureus respectively.The microbiological analysis revealed a total positivity rate of 34,5%.figure 4 shows the positivity rate according the culture requested.
The analysis of antimicrobial susceptibility tests demonstrated that 83% of CoNS were resistant to oxacilin.Regarding Pseudomonas aeruginosa and Acinetobacter spp., 85% and 50% respectively were multi-resistant.It was found one Klebisiella pneumoniae isolate resistant to carbapenems and positive to Modified Hodge Test (possible carbapenemase producing strain).
Studies show thatmales are exposed to work activities with higherrisk for accidents such ashandling equipments or chemicals, fuel, laborandelectricitynetworks 3,10 .
Regarding total body surface area (TBSA), the average percentage was 11.3%, a value close to the study conducted in Lithuania from 1991 to 2004, which averaged found was 9.6%11.Most of the burn extension was considered small, between 0 and 10% of BSA in 62 (61.4%) patients, coinciding with other studies with rates of 60.0% and 57.0%respectively 6,10 .
Inhalation injury was associated with six deaths, and the one-year mortality rate was 5.9%, higher than the study conducted by Onarheim et al. (2,1%), and Brusselaers et al.(14%)7,8.However, similar result was found at Macedo and Rosa's Brazilian study, with 6.2% mortality rate 5 .
In severely burned patients, the diagnostic of infection is extremely difficult, once inflammatory response can either cause symptoms like fever and hypotension, with increase in white blood cell account and in C-Reactive Protein (CRP).Therefore, cultures are important tools for the diagnosis of infection.
The most request culture in our service was blood culture (41%) with a posivity rate of 26.5%, followed by urine culture (18%) with positivity rate of 38% and quantitative skin biopsy (14%) with a posivity rate of 0%.Catheter tip was the fourth culture most requested, positive in 63,6%.In one study conducted in Turkey, among 169 burned patients, 127 acquired and 166 nosocomial infection (15.7% pneumonia, 56.0%BWI, 8.4% UTI and 19.9% BSI for an overall NI rate of 18.2 per 1000 patient-days) 12 .
Our analysis showed that CoNS was the most prevalent agent, mainly from blood cultures.However, it is difficult to assess the clinical importance of these pathogens as responsible for causing infection once they are also associated to skin colonization.
Although the low prevalence of Acinetobacter baumannii in burned patients according some authors, at São Paulo Hospital it was the most isolated.The Brazilian Scope Project evaluated the blood stream infection agent's prevalence and revealed a high incidence by this agent.
Pseudomonas aeruginosa is an important causative agent of infection in burns, especially skin infections.The presence of this agent is associated with high mortality rates.In this study, it was the second most prevalent agent although it has not been associated with skin infection in the sample assessed.
MEN'SHIKOV et al. ( 2009) in a specialized center for burn treatment, studied 3,179 samples of exudates from wounds and 6,501 strains of microorganisms that affect the wounds and noted that the most prevalent was Staphylococcus aureus1 4 .
At EPM/UNIFESP Burn Unit, wound secretion culture's is not recommended for routine diagnosis of infection, since it may represent colonization.The quantitative culture of a skin biopsy is the better choice to evaluate the suspecting infection.
Among 101 patients, 9 quantitative burn skin biopsy was request.None had growth of microorganisms in a significant account (> 105 UFC) and none of patients evaluated with burn skin infections.Maybe this could be attributed for the early debridement and skin graft (mean time to surgery 4.4 days).
AtEPM/UNIFESP Burn Care Unit, stringent measures area doptedin the care of burn swith daily dressing changes, wound cleaning, disinfection and use oftopical antimicrobials.GRAGNANI et al. (2005) have reported that adoption of these measure sencourages a moist environment conduciting to wound healing, mainlysuperficial 18 .
The susceptibility tests to antimicrobials showed a high frequency of multidrug-resistant microorganisms in our unit, represented mainly by Acinetobacter baumannii and Pseudomonas aeruginos are sistants to carbapenems(85% and50% respectively).From the analysed samples only one isolate of Klebsiella pneumoniae was resistant to carbapenem swith-Hodge test positive suggesting a possible carbapenemase production.
Despite the short time drive activity of the EPM/ UNIFESP Burn Care Unit, the patients studied are exposed to long periods of antibiotic therapy, which increases the selective pressure for resistant organisms(average length of stay of 13.8 days).Moreover, it is are ferral service tha treceives patients from other services(30.6%).
There ate of wound infection in burns was 0%, disagreeing with the literature.The surgical procedures(early debridementand grafting) associated with wound care such as daily dressings and topical antimicrobials, may explain the results founded.

CONCLUSIONS
The most prevalent agent was Coagulase-negative Staphylococcus in the microbiological evaluation of the firsty ear's activity of EPM/UNIFESP Burn Care Unit.Although this agent was responsable for a third of the analised cases, Gram negative bacilli, such as Pseudomonas aeruginosa and Acinetobacter baumannii, are still very prevalent, being identified in approximately half of the cultures.The long exposure to antimicrobials and high transferrate from other hospitals can explain the large number of multi resistant microorganisms in the sudy.

Figure 2 .
Figure 2. Distribution of site collection in surveillance cultures at EPM/UNIFESP Burn Unit.

Figure 3 .
Figure 3. Distribution of microorganisms isolated in surveillance cultures at EPM/ UNIFESP Burn Unit.

Figure 4 .
Figure 4. Positivity rate according the culture requested at EPM/UNIFESP Burn Unit.