a Infectious Disease Service, b Infection Control Nurse, c Microbiological Service and d Pharmacy Department, Hospital de Bellvitge, C/Feixa Larga s/n, 08907 LHospitalet de Llobregat, University of Barcelona, Barcelona, Spain
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Abstract |
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Introduction |
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In 1992, a significant increase in multi-resistant A. baumannii isolates susceptible only to imipenem, sulbactam and colistin was observed in our hospital. In spite of the introduction of an intensive control programme, the outbreak persisted and a new clone of A. baumannii appeared, which was susceptible only to colistin.5
As the digestive tract has been shown to be a major reservoir for infections in an ICU population, a possible useful effect of selective decontamination of the digestive tract (SDD) as an additional tool to help control outbreaks caused by A. baumannii has been suggested.4,6 However, the idea that both the inanimate environment and other concomitant colonized body sites such as the skin may act as additional reservoirs of infection and the extremely narrow therapeutic margin available against many A. baumannii epidemic clones cast doubt on the real efficacy of classical SDD regimens. Thus, before SDD can be considered as an additional measure to control A. baumannii outbreaks in ICU patients, we undertook the present prospective study to determine the effect of applying SDD on several body site reservoirs in ICU patients with multi-resistant A. baumannii colonization.
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Materials and methods |
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The SDD consisted of a combination of polymyxin E (150 mg), and tobramycin (80 mg), administered in 20 mL liquid form, four times per day, either orally or through a nasogastric tube. In addition, 0.5 g gel containing 2% of each of the above two antimicrobials was applied round the gum margins and oropharynx four times per day, starting on the day of detection of the A. baumannii faecal colonization and maintained until discharge from the ICU.
A. baumannii isolates were identified by the microbiology laboratory using standard biochemical reactions and their ability to grow at 37, 41 and 44°C. Antibiotic susceptibility was assessed by the microdilution method (MicroScan, NegCombo Type 6I plates; Dade International Inc., West Sacramento, CA, USA). Breakpoints for colistin were those defined by the French Society for Microbiology; isolates were considered susceptible to colistin if the MIC was 2 mg/L.
Statistical analysis
The probability of persistence of axillary, pharyngeal and rectal colonization was calculated in both groups using KaplanMeier estimates. A two-tailed P value of <0.05 was considered statistically significant. Statistical analyses were carried out with the SPSS-PC statistical package (SPSS, Chicago, IL, USA).
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Results |
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The risk of subsequent appearance of clinical colonization or infection by A. baumannii was also evaluated among the 32 patients in whom previous or simultaneous clinical samples positive for multi-resistant A. baumannii had not been detected at the time of faecal carriage: 21 of 33 (63.6%) in the control group and 11 of 21 (52.3%) in the SDD group. The development of new positive clinical samples was higher in the control group when compared with the intervention group, mainly because of the increased number of positive respiratory tract samples; also, the first positive clinical sample appeared later in the SDD group than in the control group (Table 2).
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All A. baumannii strains initially isolated in patients from the SDD group were tobramycin resistant and susceptible to colistin. No resistance to colistin developed during the study.
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Discussion |
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We used a SDD standard schedule of colistin and tobramycin, despite the fact that our A. baumannii faecal isolates were tobramycin resistant (MICs > 128 mg/L), but no other alternatives were available. The colistin dose we used (600 mg), reported in a previous study,9 was higher than that recommended (400 mg) and had no significant adverse effects.
To avoid a crossover impact,7 the control group of patients was recruited several months before, during a previous study.
The effects of SDD were significant: faecal and pharyngeal decolonization was achieved in more than half of the patients and a decrease and delay in the development of positive clinical samples was observed. In contrast, cutaneous colonization of patients was not affected by the use of SDD, confirming the importance of skin colonization as a natural habitat in the epidemiology of A. baumannii. Accordingly, clinical samples such as catheters and surgical wounds were similarly positive in both SDD patients and controls.
No development of resistance to colistin was detected in strains of A. baumannii isolated in the course of SDD. Reports of a higher number of isolations of Gram-positive microorganisms in patients following SDD have aroused some controversy, but no significant effect on clinical samples in these patients has been demonstrated.10 There were no differences regarding positive clinical samples for Gram-positive organisms in our patients.
In summary, the activity of SDD may be beneficial, decreasing the intestinal reservoir in ICU patients with A. baumannii colonization. The magnitude of the effect will depend on the resistance pattern of the strain involved and probably also on the rates of carriage on other body sites. As no effect on other ecological niches, such as patient skin colonization, was found in our study, it seems advisable that if SDD is used in the setting of an A. baumannii outbreak, decontamination should not be restricted to the digestive tract, but applied also to the skin in order to reduce the risk of persistence of a reservoir and potential recolonization of the gut. Further studies are required to show whether our findings can be replicated in other ICU settings, such as with a shorter length of stay.
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Notes |
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References |
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Received 5 February 2001; returned 13 June 2001; revised 24 August 2001; accepted 27 September 2001