Annals of Burns and Fire Disasters - vol. XI - n. 1 - March 1998

MICROBIOLOGY OF SEPTICAEMIA IN BURN PATIENTS

Sanyal S.C., Mokaddas E.M., Gang RX, Bang R.L.

Departments of Microbiology and Burns and Plastic Surgery, 1bn Sina Hospital, Kuwait

SUMMARY. A prospective study was conducted over a period of four years (July 1992-June 1996) in a burn unit to establish the actiologics of septicaemia and the number of episodes per patient and to perform antimicrobial susceptibility tests for selection of the (litig/s of choice for empiric therapy. Out of 943 patients admitted during the period, 79 (8%) suffered from 118 septicaemic episodes and Wood culture yielded 145 isolates. Seventy-two (61%) of the episodes were due to gram-positive cocci, 31 (26%) to gram-negative bacilli, one to Candida albicans and 14 to mixed infections. Of the 72 gram-positive episodes methicillin-resistant staphylococei accounted for 66 (92%). Sixty (76%) patients had a single episode, while the remainder each had 2-10 episodes. Most of the gramposilive organisms (76%) were methicillin-resistant staphylococci that were resistant to most drugs, but not glycopeptides. The gramnegalive organisms included Pseudomonas (38%), Acinetobacter (35%), and coliforms (25%). Most of the isolates of Pseudomonas were susceptible only to imipenem while those of Acinetobacter and Enterobacteriaceae were susceptible also to piperacillin/tazobactam.

Introduction

The burn injury causes devitalization of tissues and produces extensive raw areas. The wound is moist owing to flow of serous exudate at temperatures approaching 37 'C or above. The dead and denatured burn eschar and the inoist wound environment favour the colonization and prolileralion of a variety of micro-organisms.' Burn causes depression of the immune response and severe catabolism related to the extent of the burn trauma. The dysfunction of the immune SyStern,2 a large cutaneous bacterial load, the possibility of gastrointestinal bacterial translocation,' prolonged hospitalization, and invasive diagnostic and therapentic procedures all contribute to sepsis. The burn wound has a much higher incidence of infections compared with offier forms of trauma because of extensive skin barrier dismplion as well as alterationof the cellular and hurnoral immune responses.' Infection with systemic sepsis remains the Inal ' jor cause of death in burn patients. Between 63 and 75% of deaths from burn injuries in different centres were due to sepsis.' This led to the indiscriminate use of broadspeclrum antibiotics which transformed burn units into sites of multiresistant virulent microflora.
Antibiotic usage patterns effective in one centre may not be effective in another or at another time in the same unil. Each individual unit varies in its baseline population of micro-orgamsms over time, and generalizations drawn on lhe basis of results in one unit may have little appli ~,;ti)iiiiy to others.

Objectives

Enumeration of episodes of septicaemia per patient occurring during hospital stay and correlation with post-burn days

  • Prospective identification of aetiologies of septicaemia in burn patients
  • Performance of antibiotic susceptibility tests for selection of drug/s of choice for empirical therapy

Materials and methods

  • The study spanned a period of four years (July 1992June 1996) at the AI Babtain Centre Burn Unit in the Ibn Sina Hospital, Kuwait.
    All patients admitted during the period and presenting clinical signs of septicaemia were included in the study. The clinical signs noted were: reduced blood pressure, enhanced pulse rate, disorientation, hyperpyrexia or hypothermia, leucocytosis, fall in platelet count, increased sodium potassium ratio, changed colour of burn wound, petechial haemorrhage, breakdown of eschar, and loss of graft.

  • Any condition causing the slightest suspicion led to immediate collection of two-three sets of blood specimens from two different sites at an interval of at least one hour.

  • The specimens were immmediately transported to the laboratory and processed for incubation in a Bactec 9240 machine (Becton Dickinson, USA). The identification and antibiotic susceptibility of the organisms, including MIC, were performed using a Vitek machine (Bio Mereiux, Sweden). The antibiotic susceptibiliy of each isolate was retested manually according to the NCCLS recommendations for disc diffusion.'

Results

Out of the 943 patients admitted during the period, 79 (8.4%) suffered from 118 septicaemic episodes, and blood cultures yielded 145 isolates. Analysis of the aeti-
ologies of the episodes are shown in Fig. 1. Of the 72 different members of Enterobacteriaceae and other cocci in the rest.episodes of gram-positive septicaemia, methicillin-resistant staphylococci were responsible for 66 (92%). The distribution of the gram-positive and gram-negative isolates are shown in Figs. 2 and 3 respectively.

Fig. 1 - Actiologies of 118 septicaemic episodes.

Fig. 1 - Actiologies of 118 septicaemic episodes.

Sixty (76%) patients had single episodes of septicaemia, the remainder presenting two to ten episodes during their hospital stay. Fifty-four patients (68%) suffered their first episode or by day 15 post-burn, nineteen crobial combinations of the mixed infections were mostly gram-positive cocci with gram-negative bacilli (ten in number), followed by three with mixed gram-negative bacilli and one with mixed gram-positive cocci. Of the fourteen mixed infections, MRSA was involved in eight, followed by Pseudomonas in five, Acinetobacter in four, and (24%) as early as the first five days post-burn. The patients with multiple episodes usually experienced the first of these during the second week or later. Most of the gram-positive organisms were methicillin-resistant and therefore susceptible only to the glycopeptides vancomycin and teicoplanin; a small proportion were resistant to clindamycin and fusidic acid. The antibiotic resistance patterns of the gram-negative isolates are shown in Fig. 4.

Fig. 2 - Gram-positive isolates from septicaernic patients. Fig. 3 - Gram-negative isolates from septicaemic patients.
Fig. 2 - Gram-positive isolates from septicaernic patients. Fig. 3 - Gram-negative isolates from septicaemic patients.
Fig. 4 - Percentage of resistance to different antibiotics in gram-negative isolates. Fig. 4 - Percentage of resistance to different antibiotics in gram-negative isolates.

Discussion

Systemic sepsis is common in burns patients. However, the data of the present study suggest that only a small proportion of patients experience septicaemic episodes.
This study also revealed that majority of the burns patients studied suffered only a single episode of septicaemia, which in a large proportion of cases occurred during the first two weeks post-burn. The same finding was also observed in a recent retrospective report covering a period of 15 years.
Generally speaking, septicaemic episodes during the first five days post-burn are rare.' However, the observation that one-fourth of cases of the septicaemia occurred during the first five days, as noted in this study, may have been due to meticulous clinical and microbiological surveillance.
A recent report also indicated a relatively higher incidence of septicaemia during the first week post-burn.
Patients presenting multiple episodes of septicaemia usually experienced the first episode during the second week or later, probably in relation to prolonged hospital stay.
The data of the present study indicate that gram-positive cocci were dominant in the aetiology of septicaemic episodes and that methicillin-resistant staphylococci cornprised 92% of such cases. This may be due to the evolving spectrum of nosocomial pathogens in general: grampositive cocci are reported with increasing frequency in nosocomial infections.` The high incidence of methicillinresistant staphylococci may however be due to the fact that our burn unit has become endemic for such organisms." A very high occurrence of methicillin-resistant staphylococci in burn patients has also been observed elsewhere ......
Gram-negative baciffli were responsible for less than a third of the septicaemic episodes in this study. Similar observations have been made before` and are likely to be due to the general evolving trend of nosocomial infections that are specific only for burns. Pseudomonas aeruginosa has long been recognized as an important pathogen in burn infections' and the present data also indicate its predominance amongst gram-negative aerobes in the aetiology of septicaemic episodes. The emergence of Acinetobacter spp. as a frequent colonizer of burn wounds, especially since 1985, has already been observed.'The data of the present study suggest that this organism has attained a frequency almost equal to that of Pseudomonas aeruginosa in the aetiology of septicaemia.
Polymicrobial septicaemia in burns has not been repotted frequently. However, the observation made in this study that 12% of the episodes were due to mixed infections suggests that such phenomena are common. This may be due to the fact that burn patients are generally immunocompromised and therefore susceptible to multiple infections, as in malignancies. A recent report` corroborates these observations.
As already said, most of the gram-positive organisms were methicillin-resistant staphylococci and therefore susceptible only to the glycopeptides vancomyein and teicoplanin; a small proportion were susceptible to clin-damycin. Differently from some other burn centres, the MRSA isolates in this study were resistant to all other antibiotics.
The majority of the isolates of Pseudomonas were susceptible only to imipenem, while those of Acinetobacter and Enterobacteriaceae were susceptible also to piperacillin/tazobactam.
The present study thus indicates that septicaemic episodes in burn patients are caused mostly by multiresistant gram-positive cocci and aerobic gram-negative bacilli. This reduces the number of options in the selection of an antibiotic for empiric therapy.

 

RESUME. Les Auteurs ont réalisé cette étude prospective dans une unité de brûlures pendant une période de quatre ans (juillet 1992 juin 1996) pour évaluer les étiologies de la septicémie et le numéro des épisodes pour chaque patient et pour effectuer des tests de susceptibilité anti-microbienne pour la sélection des médicaments de premier choix pour la thérapie empirique. Sur 943 patients hospitalisés pendant cette période, 79 (8%) souffraient d'épisodes de septicémie. La culture du sang rendait 145 isolés. Soixante-douze (61%) des épisodes étaient causés par des cocci à gram positif, 31 (26%) par des bacilles à gram négatif, un par Candida albicans, et 14 par des infections mixtes. Sur les 72 épisodes à gram positif les Staphylococcus résistants à la méticilline étaient 66 (92%). Soixante patients (76%) ont eu un seul épisode, et les autres entre 2 e 10. La plupart des organismes à gram positif (76%) étaient des Staphy lococcus résistants à la méticilline qui étaient résistants à la majorité des médicaments, mais non aux glycopeptides. Les organismes à gram négatif comprenaient Pseudomonas (36%), Acinetobacter (35%) et des coliformes (25%). La plupart des isolés de Pseudornonas étaient susceptibles seulement à l'imipenem, tandis que ceux de Acinetobacter et des Enterobacteriaeceae étaient susceptibles aussi à la pipéracilline/tazobactam.

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This paper was received on 1 August 1997

Address correspondence to:
Dr S.C. Sanyal
Division of Microbiology, Department of Laboratory Medicine
Ibn Sina Hospital
PO Box 25427, Safat 13115, Kuwait
tel.: 0965 4845074, fax: 0965 4840836

 

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