|Year : 2020 | Volume
| Issue : 4 | Page : 339-344
Evaluation of pattern of bacterial contamination of outpatient department table surfaces in relation to cleaning and disinfection practices in a tertiary care hospital in Ahmedabad
Tanmay K Mehta1, Divya N Sharma2, Parul D Shah3
1 Assistant Professor, Department of Microbiology, Smt. N.H.L. Municipal Medical College, Ahmedabad, Gujarat, India
2 Second Year MBBS Student, Smt. N.H.L. Municipal Medical College, Ahmedabad, Gujarat, India
3 Professor and Head, Department of Microbiology, Smt. N.H.L. Municipal Medical College, Ahmedabad, Gujarat, India
|Date of Submission||25-Aug-2019|
|Date of Decision||01-Apr-2020|
|Date of Acceptance||13-Oct-2020|
|Date of Web Publication||11-Dec-2020|
Tanmay K Mehta
Department of Microbiology, Smt. NHL Municipal Medical College, Ellisbridge, Ahmedabad - 380 006, Gujarat
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Outpatient department (OPD) table surfaces frequently touched by patients and health-care workers in hospitals harbor potential pathogens and may act as source of infectious agents. Objectives: This study aimed to determine the pattern of bacterial contamination of surfaces of OPD tables in relation to existing cleaning/disinfection practices. Methods: The descriptive study was conducted during July 2018–September 2018. A total of 128 swabs were collected from 32 OPD table surfaces immediately after cleaning or disinfection and then at 30 min, 2 h, and 4 h interval after cleaning or disinfection. Type and concentration of cleaner or disinfectant, number of cleaning strokes on table, and time of last washing of cleaning cloth with detergent were also noted from each location. Isolation, identification, and antibiotic susceptibility testing of the isolates were performed by standard microbiological techniques. Results: A total of 337 bacterial isolates were recovered from 126 samples. Multidrug resistant Staphylococci, Acinetobacter, Pseudomonas, Klebsiella, and Escherichia coli were isolated. The mean bacterial colony count increased with time (P < 0.0001). Hand rub use, cleaning of OPD table surfaces with disinfectant, and more number of strokes with cleaning cloth resulted in decrease in colony count of bacteria isolated. Conclusion: High bacterial contamination of frequently touched OPD table surfaces with variety of potential pathogens like Staphylococcus, Acinetobacter, Pseudomonas, Klebsiella, and E. coli was detected. Hand hygiene among health-care workers and regular and frequent cleaning and disinfection of OPD table surfaces are highly recommended to prevent cross-transmission.
Keywords: Bacteriological contamination pattern, disinfection, hospital infection, multidrug resistant bacteria, outpatient department tables
|How to cite this article:|
Mehta TK, Sharma DN, Shah PD. Evaluation of pattern of bacterial contamination of outpatient department table surfaces in relation to cleaning and disinfection practices in a tertiary care hospital in Ahmedabad. Indian J Public Health 2020;64:339-44
|How to cite this URL:|
Mehta TK, Sharma DN, Shah PD. Evaluation of pattern of bacterial contamination of outpatient department table surfaces in relation to cleaning and disinfection practices in a tertiary care hospital in Ahmedabad. Indian J Public Health [serial online] 2020 [cited 2022 Jan 27];64:339-44. Available from: https://www.ijph.in/text.asp?2020/64/4/339/303095
| Introduction|| |
Mortality following hospital-acquired infections (HAIs) varies from 4% to 33% depending on patient population and type of health-care setting. Apart from high mortality, HAIs also cause an increase in morbidity and disabilities. The impact of HAIs is significant in terms of longer hospital treatment, readmission, surgery, work loss, and overuse of resources.
Hospital environment is the major reservoir of pathogenic microbes which pose great challenges in the hospital environment, particularly in terms of HAIs because it contains a diverse population of microorganisms. Most strains of bacteria in the health-care environments are multidrug resistant (MDR).
It has been reported that bacteria can survive for the variable duration on surfaces including white coats, stethoscopes, adhesive tape, computer keyboards, elevator buttons, mobile communication devices, and ultrasound transducers., Risk of transmission is directly proportional to the duration of survival of the bacteria on the colonized surfaces. The bacterial survival depends on various factors such as temperature, humidity, presence of organic matter, ability to form biofilms, and the prevalent infection control practices.
Outpatient department (OPD) table surfaces are most frequently touched by health-care staff, patients, relatives, and visitors. However, these surfaces are often neglected for cleaning and disinfection procedures, considering them noncritical. However, these surfaces could harbor various pathogens including multidrug resistance bacteria and can be transmitted to community by relatives and visitors as well as can cause health-care-associated infections via the hands of health-care workers.
As per the best of our knowledge till now, no study has been done to investigate bacteriological contamination of OPD table surfaces in India. Hence, we wanted to investigate profile and antimicrobial pattern of bacterial contamination of frequently touched OPD table surfaces in a tertiary care hospital. We also wanted to find out bacteriological contamination pattern in relation to cleaning/disinfection time, method, and hand sanitizer use. This information may help us to know current practices of surface disinfection in OPD settings of hospital and how to improve them. This would help to reduce the transmission of pathogens and health-care-associated infections.
| Materials and Methods|| |
Study design and setting
A prospective descriptive study was carried out at a tertiary care hospital in Ahmedabad after getting the ethical approval from the Institutional Ethic Committee from July 2018 to September 2018.
A total of 32 OPD tables in the hospital were selected for bacteriological assessment. We had an observational assessment in each OPD location during the sample collection period regarding type and concentration of cleaner or disinfectant used on the OPD table, the number of cleaning strokes on the table, and time of the last washing of cleaning cloth with detergent. These data were entered in the data record form.
Bacteriological sampling and culture and antimicrobial susceptibility testing
Surfaces of 32 OPD tables in the hospital, which patients, patients' relative, and health-care provider often interact, were sampled. From each table, four swabs were collected immediately after cleaning or disinfection and then at 30 min, 2 h, and 4 h interval after cleaning or disinfection. Hence, a total of 128 swab samples were included and examined for this study.
We have collected the specimen carefully by swabbing the surfaces using a moistened sterile swab stick with (0.9% w/v) physiological saline. All the swabs were labeled properly and transported with a minimal or no delay to the microbiology laboratory.
Each swab was inoculated onto nutrient agar, MacConkey agar, and blood agar and then agar plates were incubated aerobically for 24 h at 37°C for the primary isolation of bacteria. Identification of the isolates was done based on the standard microbiological procedures. Antimicrobial susceptibility profile of the isolates was performed and interpreted as per the Clinical Laboratory Standards Institute (CLSI) 2017 guideline based on the Kirby–Bauer agar disk-diffusion method.
Standard quality control measures were implemented throughout the whole processes of the laboratory works. All culture plates were prepared according to the manufacturers' instructions. Control bacteria strains such as Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), and Pseudomonas aeruginosa (ATCC 27853) were used to ensure the quality of culture plates and antimicrobial susceptibility testing discs.
The Institutional Ethics Committee had approved the study protocol on July 18, 2018 (Reference no: 2018-01713).
Data were entered into Microsoft Excel 2007 and descriptive statistics were used to describe studied variables. Statistical analysis was done by appropriate statistical tests using Statistical Software Package for the Social Sciences (SPSS) version 23 (SPSS Inc., Chicago, IL, USA).
| Results|| |
Of 128 swabs collected from 32 OPD tables, bacterial growth was observed in 126 (93.75%) swabs from 30 OPD tables. A total of 337 bacterial isolates were cultured from 126 sites.
Only 13 swabs (10.15%) yielded a single bacterial isolate and 115 swabs (89.85%) had multiple bacterial isolates. Gram-positive bacilli and Staphylococci were the most common isolates cultured from 122 and 114 different sites, respectively. Among Gram-negative bacteria, Acinetobacter, Pseudomonas, Klebsiella, and E. coli were isolated in decreasing order of isolation frequency. Isolated bacteria from OPD table surfaces with respect to last cleaning or disinfection time showed that the mean bacterial colony count increased with time from 28 (just after cleaning) to 43.46 (at 30 min), 70 (at 2 h), and 99.18 (at 4 h). This finding is statistically significant (P < 0.0001). A marked increase in isolation frequency of pathogenic bacteria such as Acinetobacter (6.25% to 59.37%), Pseudomonas (9.37% to 34.37%), and Klebsiella (6.25% to 28.12%) was noted just after cleaning to 4 h after the last cleaning of table. Details of specimen and bacterial isolates along with cleaning/disinfection time are depicted in [Table 1].
|Table 1: Isolated bacteria from outpatient department tables surfaces according to last cleaning/disinfection time|
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Details of isolated bacteria from OPD tables in different hospital locations are depicted in [Table 2]. All types of bacterial isolates were cultured from OPD tables from each location. However, 100% isolation frequency of Acinetobacter (ENT, pediatrics, and orthopedics), Pseudomonas (ENT), and Klebsiella (pediatrics) was notable. However, OPD tables from obstetrics and gynecology did not show growth of any Gram-negative bacteria.
|Table 2: Isolated bacteria from outpatient department tables in the hospital location wise|
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It was observed that on 13 (40.63%) OPD tables, only tap water was used for cleaning, but no surface disinfection was done (Group A). In the rest of the 19 (59.37%) OPD tables, we noted the use of Sterillium for surface disinfection without prior cleaning (Group B). Details of isolated bacteria in both the groups are depicted in [Table 3]. Although both the groups showed 100% isolation rates for Gram-positive bacteria, a significant decrease in isolation rates of Gram-negative bacteria was noted in Group B. However, Pseudomonas and E. coli showed a rise in isolation rates from OPD tables in Group B where Sterillium was used. Cleaning staff had not used any personal protective equipments (PPEs) such as gloves and mask while cleaning and disinfection. We noted that cloth used for cleaning was washed daily after use. Cleaning staff had not undergone any training for cleaning and disinfection.
|Table 3: Isolated bacteria according to cleaning/disinfection solution used, number of strokes used to clean the table, and hand sanitizer used by doctors|
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We have observed approximately up to 30% reduction in isolation rates of bacteria from OPD tables where Sterillium was used for cleaning, but three strokes were used to clean the table (Group B2) compared to tables where two strokes were used (Group B1). We have noted no difference in isolation rates of bacteria from OPD tables where only tap water (without any disinfectant) was used with one stroke (Group A1) and two strokes (Group A2). Contrary, we noted a 100% increase in isolation rates of Pseudomonas in Group A2 than Group A1. If we compare between Group A2 and Group B1 where the same number of strokes applied, there is a significant decrease of 40% in Acinetobacter colony count and 70% decrease in Pseudomonas colony count in Group B1 due to use of Sterillium [Table 3].
It was noted that the hand sanitizer Sterillium was available on all 32 OPD tables (100%). However, we have observed hand sanitizer's use before examination of each new patient on only 3 OPD tables (9.37%) from obstetrics and gynecology department (Group 2). On the rest of 29 OPD tables (90.63%), doctors were not using hand sanitizer's before examining each new patient (Group 1). There was no difference in isolation rates of Gram-positive bacilli and coagulase-negative staphylococci (CoNS) between both the groups. We found no growth of pathogenic bacteria such as Acinetobacter, Pseudomonas, Klebsiella, and E. coli on the OPD tables in Group 2 compared to those in Group 1 [Table 3].
We evaluated antibiotic susceptibility pattern of Isolated bacteria from surfaces of OPD tables were as per CLSI 2017 guideline. The Gram-positive isolates, CoNS, showed a high level of resistance against penicillin, ampicillin, cotrimoxazole, erythromycin, and clindamycin at 83.33%, 83.33% 65.78%, 59.64%, and 44.7%, respectively. In contrast, these isolates showed a low level of resistance to cefoxitin, amoxicillin/clavulanic acid, vancomycin, linezolid, and fluoroquinolones. The most common Gram-negative isolate, Acinetobacter, showed resistance to ceftriaxone, cefepime, cotrimoxazole, ciprofloxacin, gentamicin, amikacin, doxycycline, imipenem, and meropenem in more than 83% isolates. Pseudomonas also showed a high level of resistance to ciprofloxacin, levofloxacin, ceftazidime, and cefepime at 80.64%, 80.64%, 70.96%, and 70.96%, respectively. However, both Acinetobacter and Pseudomonas showed no resistance against Polymyxin B. Klebsiella and E. coli showed high resistance to cefuroxime, ceftriaxone, and cotrimoxazole at 100%.
| Discussion|| |
We noted the presence of bacterial growth on 93.75% of OPD tables immediately after cleaning which is alarming. It indicates that the procedure of cleaning and disinfection was not optimally effective. In the present study, only 10.15% of the samples yielded a single bacterial isolate and 89.85% had multiple bacterial isolates. This finding is exactly opposite to a study done by Sarwat et al. in intensive care areas where 64% of the samples yielded a single bacterial isolate and 36% had multiple bacterial isolates.
We observed an increase of mean bacterial colony count with time. It is no surprise that with increase in time, more patients, relatives, doctors, and health-care workers came into the contact with OPD table surface. Hence, we should expect an increase in bacterial contamination with the increase in time since the last cleaning of OPD tables. It can also be contributed to inefficient cleaning and disinfection of OPD tables just once before the start of the OPD which lead to survival of pathogenic bacteria on the surface. A significant increase in mean colony count started at 1 h after the cleaning.
The presence of Gram-positive bacilli from all the tables from each location was expected due to environmental and contact transmission. This can be attributed to widespread spurious presence of these bacteria in environment, air, soil, dust as well as on human skin.
In the present study, Staphylococcus was the next major Gram-positive bacterial isolate, followed by Gram-negative bacteria such as Acinetobacter and Pseudomonas. Similar pathogens were also reported in other studies.,,,,,,,,,,,, Transient colonization of hands with Gram-negative bacilli ranges from 21% to 86%.,,,,,,, In the present study, Gram-negative bacilli were seen in 78.90% of the samples positive for bacterial growth, either alone or in combination with Gram-positive bacteria. This is way more than observed in a study done by Sarwat et al.(23%).
Off late, Acinetobacter is emerging as a nosocomial pathogen.,,,,,,,,,,,, In our study also, it is seen in 37.5% of the samples showing growth and most common Gram-negative bacteria isolated. Their significance lies in their potential to become resistant to almost all antimicrobials in use which makes the treatment of HAIs difficult.
We found that 100% isolation frequency of Acinetobacter (ENT, pediatrics, and orthopedics), Pseudomonas (ENT), and Klebsiella (pediatrics) from OPD tables is scary as these bacteria are common causes of life-threatening nosocomial infections. A marked increase in isolation frequency up to 54% was noted among these Gram-negative bacteria at 4 h after the last cleaning of the OPD table. However, to our surprise, none of these Gram-negative bacteria were isolated from OPD tables from obstetrics and gynecology department despite the fact that OPD tables were cleaned with tap water only without any Sterillium or other disinfectant. We may connect this finding to the regular use of Sterillium by doctors before examining new patients in obstetrics and gynecology OPD.
We noted that both Gram-positive and Gram-negative isolates were multidrug resistant to most of the commonly used antibiotics. It is noted that most strains of bacteria in the health care environments are MDR. The widespread over and inappropriate use of antibiotics has contributed to an increased incidence of antimicrobial-resistant organisms, especially in developing countries.,, An important and worrisome consequence of HAIs is increasing antimicrobial resistance, especially in Gram-negative bacteria.,, In the past decade, virtually no new antibiotic molecule has been launched for Gram-negative bacteria. Even if new antimicrobial molecule will be found, soon they will be surpassed by emergence of new resistance mechanism by the bacteria. Hence, the only practical and logical way is to prevent and control the infections to improve the outcome and reduce the antimicrobial resistance. Furthermore, rational use of antibiotics and implementation of antibiotic stewardship also recommended.
The use of only tap water as a cleaning solution for approximately 41% of the OPD tables was an eye-opener finding. The isolation frequencies of Acinetobacter and Klebsiella were reduced from the OPD tables where Sterillium was used.
At none of the location, recommended spray-wipe-spray or wipe-discard-wipe techniques were followed. Practice of wearing PPEs by the cleaner was also missing at all the locations in our study. Cleaning was more effective in terms of decreasing isolation of bacteria up to 30% from OPD table surface by increasing the number of strokes with use of disinfectant. Cleaning by increasing the number of strokes without the use of a disinfectant using only tap water showed no change in isolation rates of bacteria but actually increased Pseudomonas isolation rates up to 100%. This demonstrated the dissemination of bacteria on OPD table surfaces if strokes are increased to clean without a disinfectant. Thus, the number of strokes of cleaning cloth also affects bacterial isolation rates from inanimate surfaces. We recommend the use of more than three strokes on an OPD table surface for effective cleaning and disinfection.
Hand hygiene is the most important and essential element of standard precautions. In the present study, we were surprised to find a 100% availability of hand sanitizer Sterillium on all the OPD tables for use by doctors and health-care workers. Unfortunately, we found that on 29 OPD tables (90.63%), it was not used before examining each new patient. Only on 3 ODP tables (9.37%) in obstetrics and gynecology department where it was used before examining, each new patient showed a 100% reduction of pathogenic bacteria such as Acinetobacter, Pseudomonas, Klebsiella, and E. coli. A study by Sarwat et al. demonstrated a 60% reduction in bacterial burden. Hand sanitizer use impact can be imagined from the fact that on these 3 OPD tables, no disinfectant or Sterillium was used for cleaning.
The study also had some limitations. The molecular characterization of the potential pathogens was not performed due to a lack of facilities. Long-term studies to establish association between pathogens isolated from inanimate OPD table surfaces and nosocomial infections in patients should be done. We could only correlate isolated bacterial pathogens with alcohol-based disinfectants and antiseptics. A similar type of studies in other hospitals with different surface disinfectants and hand rubs products can be performed. A multicenter study in tertiary care hospitals of India should be done in the research topic for generalization of results.
The study showed that present cleaning and disinfection practices need to be optimized as per the standard guidelines with any Environmental Protection Agency (EPA)-approved effective low-level disinfectant/intermediate-level disinfectant under vigilant supervision. Cleaning and disinfection of OPD tables should be done at least at 1 h interval with more than three strokes on an OPD table surface. Using hand hygiene with alcohol-based hand rub in between patients in OPD is also recommended.
| Conclusion|| |
OPD table surfaces are alarmingly contaminated with bacterial isolates and posing threats of transmission among hospital and community population. Findings of this study are important to emphasize hand hygiene and decontamination of OPD table surfaces on a regular basis and at more frequent intervals. Availability and use of hand sanitizer can reduce the possibility of transmission of potential pathogens. Decontamination of the OPD table surfaces with alcohol-based disinfectants can reduce the pathogenic microbes.
We acknowledge ICMR for financially supporting the project.
Financial support and sponsorship
STS-ICMR 2018 project.
Conflicts of interest
There are no conflicts of interest.
| References|| |
Plowman R. The socioeconomic burden of hospital acquired infection. Euro Surveill 2000;5:49-50.
Muhammad UK, Isa MA, Aliyu ZM. Distribution of potential nosocomial pathogens isolated from environments of four selected hospital in Sokoto, North Western, Nigeria. J Microbiol Biotechnol Res 2013;3:139-43.
Genet C, Kibru G, Tsegaye W. Indoor air bacterial load and antibiotic susceptibility pattern of isolates in operating rooms and surgical wards at jimma university specialized hospital, southwest ethiopia. Ethiop J Health Sci 2011;21:9-17.
Shiferaw T, Beyene G, Kassa T, Sewunet T. Bacterial contamination, bacterial profile and antimicrobial susceptibility pattern of isolates from stethoscopes at Jimma University Specialized Hospital. Ann Clin Microbiol Antimicrob 2013;12:39.
Schmidt MG, Attaway HH, Sharpe PA, John J, Sepkowitz KA, Morgan A, et al
. Sustained reduction of microbial burden on common hospital surfaces through introduction of copper. J Clin Microbiol 2012;50:2217-23.
Kramer A, Schwebke I, Kampf G. How long do nosocomial pathogens persist on inanimate surfaces? A systematic review. BMC Infect Dis 2006;6:130.
Cheesbrough M. Manual of Medical Microbiology. Britain, UK: Oxford Press; 2000.
Clinical Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial Susceptibility Testing, Twenty Second Information. Vol. 35. USA: Clinical Laboratory Standards Institute (CLSI); 2017.
Sarwat F, Surraiya BK, Aarthi VS. To compare the efficacy of three different hand hygiene agents in reducing the bacterial load from hands in intensive care areas of a tertiary care hospital. Int J Curr Microbiol App Sci 2015;4:90-7.
Gastmeier P, Sohr D, Geffers C, Nassauer A, Dettenkofer M, Rüden H. Occurrence of methicillin-resistant Staphylococcus aureus
infections in German intensive care units. Infection 2002;30:198-202.
Saka KH, Akanbi II AA, Obasa TO, Raheem RA, Oshodi AJ. Bacterial contamination of hospital surfaces according to material make, last time of contact and last time of cleaning/disinfection. J Bacteriol Parasitol 2017;8:312.
Ulger F, Esen S, Dilek A, Yanik K, Gunaydin M, Leblebicioglu H. Are we aware how contaminated our mobile phones with nosocomial pathogens? Ann Clin Microbiol Antimicrob 2009;8:7.
Teng SO, Lee WS, Ou TY, Hsieh YC, Lee WC, Lin YC. Bacterial contamination of patients' medical charts in a surgical ward and the intensive care unit: Impact on nosocomial infections. J Microbiol Immunol Infect 2009;42:86-91.
Mullaney PJ, Munthali P, Vlachou P, Jenkins D, Rathod A, Entwisle J. How clean is your probe? Microbiological assessment of ultrasound transducers in routine clinical use, and cost-effective ways to reduce contamination. Clin Radiol 2007;62:694-8.
Lawrence MW, Blanks J, Ayala R, Talk D, Macian D, Glasser J, et al
. Hospital-wide survey of bacterial contamination of point-of-care ultrasound probes and coupling gel. J Ultrasound Med 2014;33:457-62.
Koibuchi H, Kotani K, Taniguchi N. Ultrasound probes as a possible vector of bacterial transmission. J Med Ultrason 2013;15:41-4.
Koibuchi H, Hayashi S, Kotani K, Fujii Y, Konno K, Hirai Y, et al
. Comparison of methods for evaluating bacterial contamination of ultrasound probes. J Med Ultrason 2009;36:187.
Ohara T, Itoh Y, Itoh K. Contaminated ultrasound probes: A possible source of nosocomial infections. J Hosp Infect 1999;43:73.
Levin PD, Shatz O, Sviri S, Moriah D, Or-Barbash A, Sprung CL, et al
. Contamination of portable radiograph equipment with resistant bacteria in the ICU. Chest 2009;136:426-32.
Whittington AM, Whitlow G, Hewson D, Thomas C, Brett SJ. Bacterial contamination of stethoscopes on the intensive care unit. Anaesthesia 2009;64:620-4.
Hailu G, Awoke D, Daniel M. Surfaces and air bacteriology of selected wards at a referral hospital, Northwest Ethiopia: A cross-sectional study. Int J Microbiol 2018;2018:6413179.
Richards MJ, Edwards JR, Culver DH, Gaynes RP. Nosocomial infections in medical intensive care units in the United States. National Nosocomial Infections Surveillance System. Crit Care Med 1999;27:887-92.
Diriba L, Kassaye A, Yared M. Antibiotics susceptibility pattern of hospital indoor airborne bacteria in Hawassa University Teaching and Referral Hospital, South Ethiopia. Int J Mod Chem Appl Sci 2016;3:287-92.
Mengistu H, Misganaw B, Elshaday A. Bacterial load and antibiotic susceptibility pattern of isolates in operating rooms at Hawassa University Referral Hospital, southern Ethiopia. J Microbiol Antimicrob 2016;8:1-6.
Tesfaye T, Berhe Y, Gebreselassie K. Microbial contamination of operating theatre at Ayder Referral Hospital, Northern Ethiopia. Int J Pharm Sci Res 2015;10:975-92.
Siegel RE. Emerging gram-negative antibiotic resistance: Daunting challenges, declining sensitivities, and dire consequences. Respir Care 2008;53:471-9.
Lockhart SR, Abramson MA, Beekmann SE, Gallagher G, Riedel S, Diekema DJ, et al
. Antimicrobial resistance among Gram-negative bacilli causing infections in intensive care unit patients in the United States between 1993 and 2004. J Clin Microbiol 2007;45:3352-9.
Slama TG. Gram-negative antibiotic resistance: There is a price to pay. Crit Care 2008;12(Suppl 4):S4.
Chopra I, Schofield C, Everett M, O'Neill A, Miller K, Wilcox M, et al
. Treatment of health-care-associated infections caused by Gram-negative bacteria: A consensus statement. Lancet Infect Dis 2008;8:133-9.
[Table 1], [Table 2], [Table 3]