Letters
330
to the Editor
Sir, Selective
digestive
tract decontamination Gram-negative bacteria
and environmental
Selective digestive tract decontamination (SDD) has been advocated to reduce infection acquired in Intensive Care Units (ICUS).‘-~ However, concern has been expressed about the potential to select for resistant bacteria, especially Gram-negative bacilli.4,5 Armstrong and colleagues have recently reported that 77% of 108 environmental isolates of Pseudomonas recovered from sinks, humidified water and breathing circuits were Pseudomonas aeruginosa and were of similar pyocin type to isolates recovered from patients.6 Environmental sites were sampled three times during the course of an SDD study carried out in a surgical ICU at the Bristol Royal Infirmary between 1988 and 1990. The SDD regimen consisted of polymyxin E, tobramycin and amphotericin B applied to the buccal mucosa and via a nasogastric tube in patients likely to remain on the unit for 48 h or longer, for the first 3 with intravenous ceftazidime 50 mg kg -’ day-’ administered days only. Sampling of the environment was carried out 1 month before, 12 months after SDD was introduced and finally, 1 month after SDD had been discontinued. Full details of the methods and results of this trial are discussed elsewhere.7 Twenty-five sites inside and immediately outside the ICU including sinks, bedpan washers, air vents and windows, were sampled with moistened standard ‘Transwabs’ (Technical Service Consultants, UK). The ‘M’ technique was used to semi-quantitate numbers of organisms present.8 Gram-negative bacilli were identified on the basis of Gram’s stain, colonial morphology, oxidase reaction and a series of biochemical profiles with the API 20NE and API 20E systems (bio-Merieux). Sensitivity testing was carried out to ampicillin, ceftazidime, cefotaxime, gentamicin, tobramycin and ciprofloxacin by an agar incorporation technique’ and isolates were deemed sensitive or resistant with reference to recommended breakpoints.” The distribution of isolates recovered from environmental sites is outlined in Table I. The majority of sites were colonized by small numbers of mainly oxidase-positive Gram-negative bacilli. Approximately one third of isolates were Pseudomonas spp. including Pseudomonas acidovorans, Pseudomonas putrefaciens and Pseudomonas stutxeri. Pseudomonas aeruginosa was not recovered from sites sampled outside the ICU or from the sluice room and accounted for less than 10% of total isolates. More isolates were recovered from samples taken during or following the use of SDD compared with before its introduction (27 during SDD, 23 post-SDD vs. 16 pre-SDD) but this was not statistically significant. The number of bacteria recovered from environmental sites in an ICU will vary from time to time and fluctuate according to the number and type of patients present and the sensitivity of laboratory methods used.
Letters Table
I. Distribution
to the Editor
of Gram-negative bacilli isolated from sites inside and outside the ICU during and after use of SDD P. aerueinosa
Outside Sluice
ICU room
Assessment and Procedure room Other sites Sub-totals
Pre-SDD During SDD Post-SDD Pre-SDD During SDD Post-SDD Pre-SDD Durirw SDD Post-SDD Pre-SDD During SDD Post-SDD Pre-SDD During SDD Post-SDD
Total * Including
331
Acinetobacter SFP., Flawbacterium
Pseudomonas Xanthomonas maltophilia SPP. 4
1 5 4 3
1 1 1 0 0 2
Others*
0 1
Total
2 1
4 6
: 5 6
:: 9 11
0 0 2 1 5
before,
;
1 2 3
: 0
13 6
: 4 4
25 6 10
: 9 3 16 27 22
26
12
21
65
0
meningosepticum and Alcaligenes spp
Consequently, surveillance over a longer period would be required to detect major changes in ICU flora as a result of the introduction of SDD. Sampling was carried out on only three occasions making this a very limited study. Resistance to ceftazidime increased from 62% before to 85% during and 91% after discontinuation of SDD but this is not statistically significant. There were no diagnosed or suspected infections caused by ceftazidime- or tobramycin-resistant Gram-negative bacilli during the SDD trial.7 Environmental surveillance is not indicated as a routine infection control measure and a more comprehensive study carried out over a longer period of time than that reported here would be required to examine the interrelationship between SDD, patients’ flora and environmental organisms. The use of SDD may select antibiotic-resistant Gram-negative bacilli in symptomatic or asymptomatic patients which in turn may spread to the environment and become a potential source of infection. However, it is difficult to assess the extent of this risk. Most ICU-acquired infections arise from the patient’s endogenous flora and apart from occasional epidemics, environmental sources are rarely implicated. Furthermore, SDD regimens have been employed successfully to control outbreaks of infection caused by resistant bacteria. 11,12During one outbreak caused by Klebsiella aerogenes, environmental screening did not uncover a reservoir and was not considered useful in controlling spread.” The majority of our isolates were low-grade pathogens and P. aeruginosa accounted for a smaller proportion compared with the study of Armstrong and colleagues6 who
332
Letters
to the Editor
suggest that resistant strains may spread between patients and the environment. Whatever the potential risk to patients of colonization with resistant bacteria may be, we -agree that strict infection control measures must be maintained to reduce cross-infection. We are grateful to Professor D. C. E. Speller for his helpful advice during the conduct study and to Dr S. M. Willatts and Dr R. Winter for statistical analysis.
A. A. A. H.
Sternberg Smith Pick Humphreys
of this
Department of Microbiology, Bristol Royal Infirmary, Marlborough Street, Bristol BS2 8HW, UK
Department Correspondence to: H. Humphreys, Medical Centre, Nottingham NG7 2UH, UK.
of Microbiology,
University
Hospital,
Queen’s
References 1. Stoutenbeek Nosocomial
CP, van Saene HKF? Gram-negative pneumonia
Miranda in critically
DR, Zandstra DF, Langrehr D. ill patients. 1nntensive Cure Med 198;
12: 419-423. IMcA, 2. Ledingham
Alcock SR, Eastaway AE, McDonald JC, McKay IC, Ramsay G. Triple regimen of selective decontamination of the digestive tract, systemic cefotaxime, and microbiological surveillance for prevention of acquired infection in intensive care.
Lancet 1988; i: 785-790. K, Ruckdeschel 3. Unertl
G, Selbmann KH et al. Prevention of colonization and in long-term ventilated patients by local antimicrobial prophylaxis Intensive Care Med 1987; 13: 106-I 13. Sanderson PJ. Selective decontamination of the digestive tract. Value in intensive care units not proved. Br MedJ 1989; 299: 1413-1414. Nau R, Ruchel R, Mergerian H, Wegner U, Winklemann T, Prange H. Emergence of antibiotic-resistant bacteria during selective decontamination of the digestive tract. r Antimicrob Chemother 1990; 25: 881-882. Armstrong PJ, Barr JG, Webb CH, Blair PH, Rowlands BJ. Epidemiology of Pseudomonas aeruginosa in an intensive care unit using selective decontamination of the digestive tract. J Hosp Infect 1992; 20: 199-208. Winter R, Humphreys H, Pick A, MacGowan AP, Willatts SM, Speller DCE. A controlled trial of selective decontamination of the digestive tract in intensive care and its effect on nosocomial infection. J Antimicrob Chemother 1992; 30: 73-87. Lewis DA, Leaper DJ, Speller DCE. Prevention of bacterial colonization of wounds at operation. J Hosp Infect 1984; 5: 431-437. Holt AH, Brown D. Antimicrobial susceptibility testing. In: Hawkey PM, Lewis DA, Eds. Medical Bacteriology. A Practical Approach. Oxford: IRL Press 1989; 167-194. Report of the Working Party on Antibiotic Sensitivity testing of the British Society for Antimicrobial Chemotherapy. J Antimicrob Chemother 1991; 27(Suppl. D): 9. Brun-Buisson C, Legrand P, Rauss A et al. Intestinal decontamination for control of nosocomial multiresistant Gram-negative bacilli. Ann Intern Med 1989; 110: 873-881. Taylor ME, Oppenheim BA. Selective decontamination of the gastrointestinal tract as an infection control measure. J Hosp Infect 1991; 17: 271-278. respiratory
4. 5. 6. 7. 8. 9. 10. Il. 12.
infections
330
to the Editor
Sir, Selective
digestive
tract decontamination Gram-negative bacteria
and environmental
Selective digestive tract decontamination (SDD) has been advocated to reduce infection acquired in Intensive Care Units (ICUS).‘-~ However, concern has been expressed about the potential to select for resistant bacteria, especially Gram-negative bacilli.4,5 Armstrong and colleagues have recently reported that 77% of 108 environmental isolates of Pseudomonas recovered from sinks, humidified water and breathing circuits were Pseudomonas aeruginosa and were of similar pyocin type to isolates recovered from patients.6 Environmental sites were sampled three times during the course of an SDD study carried out in a surgical ICU at the Bristol Royal Infirmary between 1988 and 1990. The SDD regimen consisted of polymyxin E, tobramycin and amphotericin B applied to the buccal mucosa and via a nasogastric tube in patients likely to remain on the unit for 48 h or longer, for the first 3 with intravenous ceftazidime 50 mg kg -’ day-’ administered days only. Sampling of the environment was carried out 1 month before, 12 months after SDD was introduced and finally, 1 month after SDD had been discontinued. Full details of the methods and results of this trial are discussed elsewhere.7 Twenty-five sites inside and immediately outside the ICU including sinks, bedpan washers, air vents and windows, were sampled with moistened standard ‘Transwabs’ (Technical Service Consultants, UK). The ‘M’ technique was used to semi-quantitate numbers of organisms present.8 Gram-negative bacilli were identified on the basis of Gram’s stain, colonial morphology, oxidase reaction and a series of biochemical profiles with the API 20NE and API 20E systems (bio-Merieux). Sensitivity testing was carried out to ampicillin, ceftazidime, cefotaxime, gentamicin, tobramycin and ciprofloxacin by an agar incorporation technique’ and isolates were deemed sensitive or resistant with reference to recommended breakpoints.” The distribution of isolates recovered from environmental sites is outlined in Table I. The majority of sites were colonized by small numbers of mainly oxidase-positive Gram-negative bacilli. Approximately one third of isolates were Pseudomonas spp. including Pseudomonas acidovorans, Pseudomonas putrefaciens and Pseudomonas stutxeri. Pseudomonas aeruginosa was not recovered from sites sampled outside the ICU or from the sluice room and accounted for less than 10% of total isolates. More isolates were recovered from samples taken during or following the use of SDD compared with before its introduction (27 during SDD, 23 post-SDD vs. 16 pre-SDD) but this was not statistically significant. The number of bacteria recovered from environmental sites in an ICU will vary from time to time and fluctuate according to the number and type of patients present and the sensitivity of laboratory methods used.
Letters Table
I. Distribution
to the Editor
of Gram-negative bacilli isolated from sites inside and outside the ICU during and after use of SDD P. aerueinosa
Outside Sluice
ICU room
Assessment and Procedure room Other sites Sub-totals
Pre-SDD During SDD Post-SDD Pre-SDD During SDD Post-SDD Pre-SDD Durirw SDD Post-SDD Pre-SDD During SDD Post-SDD Pre-SDD During SDD Post-SDD
Total * Including
331
Acinetobacter SFP., Flawbacterium
Pseudomonas Xanthomonas maltophilia SPP. 4
1 5 4 3
1 1 1 0 0 2
Others*
0 1
Total
2 1
4 6
: 5 6
:: 9 11
0 0 2 1 5
before,
;
1 2 3
: 0
13 6
: 4 4
25 6 10
: 9 3 16 27 22
26
12
21
65
0
meningosepticum and Alcaligenes spp
Consequently, surveillance over a longer period would be required to detect major changes in ICU flora as a result of the introduction of SDD. Sampling was carried out on only three occasions making this a very limited study. Resistance to ceftazidime increased from 62% before to 85% during and 91% after discontinuation of SDD but this is not statistically significant. There were no diagnosed or suspected infections caused by ceftazidime- or tobramycin-resistant Gram-negative bacilli during the SDD trial.7 Environmental surveillance is not indicated as a routine infection control measure and a more comprehensive study carried out over a longer period of time than that reported here would be required to examine the interrelationship between SDD, patients’ flora and environmental organisms. The use of SDD may select antibiotic-resistant Gram-negative bacilli in symptomatic or asymptomatic patients which in turn may spread to the environment and become a potential source of infection. However, it is difficult to assess the extent of this risk. Most ICU-acquired infections arise from the patient’s endogenous flora and apart from occasional epidemics, environmental sources are rarely implicated. Furthermore, SDD regimens have been employed successfully to control outbreaks of infection caused by resistant bacteria. 11,12During one outbreak caused by Klebsiella aerogenes, environmental screening did not uncover a reservoir and was not considered useful in controlling spread.” The majority of our isolates were low-grade pathogens and P. aeruginosa accounted for a smaller proportion compared with the study of Armstrong and colleagues6 who
332
Letters
to the Editor
suggest that resistant strains may spread between patients and the environment. Whatever the potential risk to patients of colonization with resistant bacteria may be, we -agree that strict infection control measures must be maintained to reduce cross-infection. We are grateful to Professor D. C. E. Speller for his helpful advice during the conduct study and to Dr S. M. Willatts and Dr R. Winter for statistical analysis.
A. A. A. H.
Sternberg Smith Pick Humphreys
of this
Department of Microbiology, Bristol Royal Infirmary, Marlborough Street, Bristol BS2 8HW, UK
Department Correspondence to: H. Humphreys, Medical Centre, Nottingham NG7 2UH, UK.
of Microbiology,
University
Hospital,
Queen’s
References 1. Stoutenbeek Nosocomial
CP, van Saene HKF? Gram-negative pneumonia
Miranda in critically
DR, Zandstra DF, Langrehr D. ill patients. 1nntensive Cure Med 198;
12: 419-423. IMcA, 2. Ledingham
Alcock SR, Eastaway AE, McDonald JC, McKay IC, Ramsay G. Triple regimen of selective decontamination of the digestive tract, systemic cefotaxime, and microbiological surveillance for prevention of acquired infection in intensive care.
Lancet 1988; i: 785-790. K, Ruckdeschel 3. Unertl
G, Selbmann KH et al. Prevention of colonization and in long-term ventilated patients by local antimicrobial prophylaxis Intensive Care Med 1987; 13: 106-I 13. Sanderson PJ. Selective decontamination of the digestive tract. Value in intensive care units not proved. Br MedJ 1989; 299: 1413-1414. Nau R, Ruchel R, Mergerian H, Wegner U, Winklemann T, Prange H. Emergence of antibiotic-resistant bacteria during selective decontamination of the digestive tract. r Antimicrob Chemother 1990; 25: 881-882. Armstrong PJ, Barr JG, Webb CH, Blair PH, Rowlands BJ. Epidemiology of Pseudomonas aeruginosa in an intensive care unit using selective decontamination of the digestive tract. J Hosp Infect 1992; 20: 199-208. Winter R, Humphreys H, Pick A, MacGowan AP, Willatts SM, Speller DCE. A controlled trial of selective decontamination of the digestive tract in intensive care and its effect on nosocomial infection. J Antimicrob Chemother 1992; 30: 73-87. Lewis DA, Leaper DJ, Speller DCE. Prevention of bacterial colonization of wounds at operation. J Hosp Infect 1984; 5: 431-437. Holt AH, Brown D. Antimicrobial susceptibility testing. In: Hawkey PM, Lewis DA, Eds. Medical Bacteriology. A Practical Approach. Oxford: IRL Press 1989; 167-194. Report of the Working Party on Antibiotic Sensitivity testing of the British Society for Antimicrobial Chemotherapy. J Antimicrob Chemother 1991; 27(Suppl. D): 9. Brun-Buisson C, Legrand P, Rauss A et al. Intestinal decontamination for control of nosocomial multiresistant Gram-negative bacilli. Ann Intern Med 1989; 110: 873-881. Taylor ME, Oppenheim BA. Selective decontamination of the gastrointestinal tract as an infection control measure. J Hosp Infect 1991; 17: 271-278. respiratory
4. 5. 6. 7. 8. 9. 10. Il. 12.
infections
