Objectives: The objectives of this study were to determine the frequency of methicillin-resistant Staphylococcus aureus (MRSA) colonization or infection while on admission to the intensive care unit (ICU), and examine the genetic backgrounds of the MRSA isolates to establish transmission among the patients. Subjects and Methods: This study involved screening 2,429 patients admitted to the ICU of Farwania Hospital from January 2005 to October 2007 for MRSA colonization or infection. The MRSA isolates acquired after admission were investigated using a combination of molecular typing techniques to determine their genetic backgrounds. Results: Of 2,429 patients screened, 25 (1.0%) acquired MRSA after admission to the ICU. Of the 25 MRSA, 19 (76%) isolates belonged to health care-associated (HA-MRSA) clones: ST239-III (n = 17, 68%) and ST22-IV (n = 2, 8%). The remaining 6 MRSA isolates belonged to community-associated clones: ST80-IV (n = 3, 12%), ST97-IV (n = 2, 8%), and ST5-IV (n = 1, 4%). The ST239-III-MRSA clone was associated with infection as well as colonization, and was isolated from patients from 2005 to 2007. Conclusions: The HA-MRSA clone ST239-III persistently colonized patients admitted to the ICU, indicating the possibility of its transmission among the patients over time.

Since its first description reported from the UK in 1961, methicillin-resistant Staphylococcus aureus (MRSA) has become a major cause of infections in both hospitals and the community [1,2,3,4,5], although the prevalence seems to vary according to the geographic location, type of health care facility, and the specific population being studied [5]. The prevalence of MRSA in a hospital setting, such as a tertiary care facility or intensive care unit (ICU), had been reported to be approximately 60-70% of all S. aureus isolates [5,6]. The ICU is among the most affected areas in a hospital where patients are at a higher risk of acquiring MRSA [2,7]. In contrast to the prevalence of MRSA colonization or infection in the ICU, which has been reported to be 4-8% [2,8], the prevalence in general in-patient setting varies from 0.18 to 7.2% [5,6,7,8,9].

Surveillance studies have shown that old age, male gender, and previous hospital admission are risk factors for acquisition of MRSA in patients undergoing surgical treatment [10]. Some of the important risk factors for acquisition and colonization of MRSA are use of extended-spectrum antimicrobial agents [4] and prolonged duration of antimicrobial therapy [3], whereas inappropriate antimicrobial therapy, comorbid conditions, and advanced patient age cause increased mortality associated with systemic MRSA infections [5]. Risk factors associated with MRSA acquisition in the ICU setting include prolonged stay, use of intravascular devices, and the intensity of exposure to colonized or infected patients [5].

Molecular epidemiology of MRSA has enhanced the understanding of the dynamics of acquisition and spread of community-acquired (CA-MRSA) and health care-acquired MRSA (HA-MRSA) in health care facilities. The CA-MRSA strains are distinguished by their carriage of types IV or V staphylococcal cassette chromosome mec (SCCmec) elements [11,12], whereas HA-MRSA strains carry the SCCmec types I, II, and III [13].

Although MRSA are regularly isolated from patients at Farwania Hospital, there are no data on MRSA colonization of patients admitted to the ICU of this hospital. This study was conducted to determine the prevalence of MRSA colonization at admission or during ICU stay, and its impact on subsequent MRSA infection. The study also investigated the genetic backgrounds of the MRSA isolates to understand whether they were being transmitted among patients admitted to the ICU.

Active Surveillance, Decolonization, and Infection Control Measures

Farwania Hospital serves a population of approximately 700,000 in Kuwait. The ICU has 17 beds, including 2 side rooms, and admits adult in-patients from all specialties within the hospital, emergency room, and those transferred from other hospitals. The medical records of 2,429 patients admitted to the ICU from January 1, 2005 to October 31, 2007 were reviewed for colonization and/or infection with MRSA. Three sites, anterior nares, axillae, and groin, were screened at the time of admission to the ICU and weekly thereafter. If MRSA was isolated from any of the 3 screening specimens at the time of admission, the patient was identified as having been initially colonized. If the admission cultures were negative but subsequent cultures from any site during the course of ICU stay grew MRSA, the patient was identified as having acquired MRSA after admission. MRSA-positive patients were isolated in one of the side rooms or cohorted with other positive patients. Decolonization was attempted for MRSA-positive patients who were treated for 5 days with 2% mupirocin ointment for anterior nares, whereas repeated bathing with chlorhexidine was used when the other 2 body sites tested positive for MRSA. Patients were then retested for 3 consecutive days to ensure clearance. Patients with positive MRSA from blood cultures or those who were diagnosed with ventilator-associated pneumonia due to MRSA were treated with intravenous vancomycin or teicoplanin. Nurses who attended MRSA-positive patients did not care for MRSA-negative patients, and the staff attending positive patients followed strict contact precautions according to hospital infection control policy. At the time of the patient's discharge from the ICU, terminal cleaning was undertaken using 1% hypochlorite solution for bed rails, floor, walls, and curtains.

Culture and Identification of MRSA Strains

Surveillance specimens from anterior nares, axillae, and groin as well as clinical samples from other diagnostically relevant sites were cultured on 5% sheep blood agar and mannitol salt agar plates for the isolation of S. aureus. Both media were incubated for 24 h at 37°C. Conventional methods including Gram's stain, tube coagulase, and DNase tests and the automated identification system VITEK 2 (bioMerieux, Marcy l'Etoile, France) or Phoenix (Becton Dickinson, USA) were used to identify suspected S. aureus colonies. Isolates were preserved in glycerol 15% (v/v) in brain-heart infusion broth (Oxoid, Basingstoke, UK) at -80°C for further analysis.

Antibiotic Susceptibility Testing

The disk diffusion method was used to perform antimicrobial susceptibility and interpreted according to the Clinical and Laboratory Standard Institutes (CLSI) guidelines [14] with the following antimicrobial disks (Oxoid): benzyl penicillin (2 U), cefoxitin (30 µg), kanamycin (30 µg), mupirocin (200 µg), gentamicin (10 µg), erythromycin (15 µg), clindamycin (2 µg), chloramphenicol (30 µg), tetracycline (10 µg), trimethoprim (2.5 µg), fusidic acid (10 µg), rifampicin (5 µg), ciprofloxacin (5 µg), and linezolid (30 µg). The minimum inhibitory concentration for cefoxitin, vancomycin, and teicoplanin was determined with Etest strips (bioMerieux) according to the manufacturer's instructions. S. aureus strain ATCC25923 was used as a quality control strain for susceptibility testing. Methicillin resistance was confirmed by detecting PBP 2a using a rapid latex agglutination kit (Denka-Seiken, Japan) according to the manufacturer's instruction.

Molecular Typing of MRSA Isolates

Pulsed-field gel electrophoresis, coagulase gene typing, SCCmec typing, Spa typing, and multilocus sequence typing were used to perform genotypic characterization of the MRSA isolates. Pulsed-field gel electrophoresis was performed as described previously [15]. Coagulase gene typing was performed using published primers and protocols as described by Goh et al. [16]. SCCmec typing was performed by PCR assays as described previously [17,18]. Spa typing was performed as described by Harmsen et al. [19] for all MRSA isolates. Multilocus sequence typing was performed on all isolates as described by Enright et al. [20].

Of the 2,429 patients admitted to the ICU for MRSA carriage, 18 (0.74%) were colonized and 2 (0.08%) were infected (one was diagnosed with pneumonia and the other with gluteal abscess) on admission. Of the 18 colonized patients, 1 (5%) developed blood stream infection on day 21 of the ICU stay. Of 2,409 patients not colonized or infected with MRSA at admission, 25 (1.0%) acquired MRSA in the ICU after stays of 7-54 days. Of these 25 patients, 18 (72%) were identified with colonization only, whereas 7 (28%) were colonized and or infected. The demographic characteristics of the MRSA-positive patients are shown in Table 1. The 25 MRSA isolates acquired after admission were investigated further to determine their genetic relatedness.

Table 1

Demographic characteristics of methicillin-resistant Staphylococcusaureus (MRSA)-positive patients

Demographic characteristics of methicillin-resistant Staphylococcusaureus (MRSA)-positive patients
Demographic characteristics of methicillin-resistant Staphylococcusaureus (MRSA)-positive patients

Molecular Typing of MRSA Acquired in the ICU

The genetic backgrounds and antibiotic resistance patterns of those isolates are presented in Table 2. Seventeen (68%) of the 25 isolates belonged to the ST239-III-MRSA clone (a health care-associated MRSA clone), while the remaining 8 (32%) isolates belonged to 4 different community-associated MRSA clones consisting of three ST80-IV-MRSA, two ST-22-IV-MRSA, two ST97-IV-MRSA, and one ST5-IV-MRSA. Spa typing revealed that the seventeen ST239-III-MRSA isolates belonged to 2 dominant subtypes consisting of eight t421 and six t945 and two minor subtypes consisting of two t388 and one t4410. The dominant ST239-III-MRSA strains were isolated from both colonized and infected patients. The ST239-MRSA isolates were resistant to multiple antibiotics including tetracycline, aminoglycosides, erythromycin, clindamycin, and fusidic acid. One isolate obtained in 2006 expressed high-level mupirocin resistance. The other MRSA clones, ST80-IV, ST22-IV, and ST97-IV, were non-multidrug-resistant. All isolates were susceptible to vancomycin, teicoplanin, linezolid, and rifampicin.

Table 2

Antimicrobial resistance pattern and molecular typing results of 25 strains of methicillin-resistant Staphylococcusaureus (MRSA) acquired in the ICU

Antimicrobial resistance pattern and molecular typing results of 25 strains of methicillin-resistant Staphylococcusaureus (MRSA) acquired in the ICU
Antimicrobial resistance pattern and molecular typing results of 25 strains of methicillin-resistant Staphylococcusaureus (MRSA) acquired in the ICU

The results of this study revealed that 1.0% of patients admitted to the ICU became colonized or infected with MRSA 7-54 days after admission, which confirmed the findings of previous studies [21,22] that admission to the ICU is a risk factor for MRSA colonization and infection. The study also revealed that more patients (1%) acquired MRSA after admission to the ICU than those colonized prior to admission (0.74%), further strengthening the notion that admission to the ICU is a risk factor for MRSA acquisition [21,22]. The 0.74% prevalence of MRSA among patients at the time of admission to the ICU in this study was comparable to an earlier study from our geographical region (Saudi Arabia) that reported prevalence of MRSA colonization at the time of admission to be 1.1% [23]. However, other studies have shown different prevalence rates of MRSA colonizing patients at the time of admission to ICU, which ranged from 2.5 to 46% [10,24,25,26], probably reflecting a higher rate of MRSA colonization in the community prior to hospital admission. However, a study from Brazil which reported a higher frequency (46%) of colonization with MRSA at the time of admission with 52% of the patients acquiring it in the ICU, did not find any association with identifiable risk factors although the unusually higher rates of MRSA acquisition among their patient population in the ICU was attributed to improper hand-washing, environmental surface cleaning, and barrier protection from infected patients, unlike infection control procedures adopted in our ICU [26].

MRSA acquisition often results in increased length of hospital stay as seen in the present study. The patients in this study acquired MRSA after 7 days of ICU admission which resulted in 30.5 days average length of hospital stay. This was much longer than the 7.2 days stay in the ICU reported by Marshall et al. [27] with 12.8% of their patients acquiring MRSA (colonization/infection) after 5 days of admission to the ICU.

In this study, the dominant MRSA clone acquired in the ICU belonged to a well-known health care-associated clone, ST239-III MRSA. In contrast, Kwon et al. [6], who investigated the relationship between MRSA strains isolated from ICU patients with bacteremia and nasal colonization, observed that a clone belonging to the pulsed-field gel electrophoresis type B (SCCmec type II/ST5) genotype, which represented another hospital-acquired genotype, was the dominant clone acquired in the ICU in Korea.

This study also revealed that the same MRSA clone was involved in colonization as well as in infection, and was isolated from patients admitted to the ICU from 2005 to 2007, indicating a persistence of the ST239-III clone in the ICU. Persistence of the MRSA clone in the ICU could be due to environmental contamination or carriage of the MRSA clone by health care workers in the ICU or both. Unfortunately, neither the environment nor health care workers were screened as part of this study.

In this study, 1.0% of patients admitted to the ICU of a Farwania General Hospital in Kuwait acquired MRSA while on admission. Most of the patients were colonized or infected by a health care-associated ST239-III-MRSA clone which persisted in the facility over time. Hence, screening patients for MRSA is strongly advocated to detect carriers and enforce decontamination procedures, which can reduce infections and prevent transmission to others. Further research is needed to identify effective methods for sustained eradication of MRSA carriage to reduce the probability of subsequent infection in the high-risk population.

Barber M: Methicillin-resistant staphylococci. J Clin Pathol 1961;14:385-393.
Grundmann H, Hori S, Winter B, et al: Risk factors for transmission of methicillin-resistant Staphylococcus aureus in an adult intensive care unit: fitting a model to the data. J Infect Dis 2002;185:481-488.
Corea E, de Silva T, Perera J: Methicillin-resistant Staphylococcus aureus: prevalence, incidence and risk factors associated with colonization in Sri Lanka. J Hosp Infect 2003;55:145-148.
Wang JT, Liao CH, Fang CT, et al: Incidence of and risk factors for community-associated methicillin-resistant Staphylococcus aureus acquired infection or colonization in intensive care unit patients. J Clin Microbiol 2010;48:4439-4444.
Davis KA, Stewart JJ, Crouch HK, et al: Methicillin-resistant Staphylococcus aureus (MRSA) nares colonization at hospital admission and its effect on subsequent MRSA infection. Clin Infect Dis 2004;39:776-782.
Kwon JC, Kim SH, Park SH, et al: Molecular epidemiologic analysis of methicillin-resistant Staphylococcus aureus isolates from bacteremia and nasal colonization at 10 intensive care units: multicenter prospective study in Korea. J Korean Med Sci 2011;26:604-611.
Jakob SM, Rothen H: Intensive care 1980-1995: change in patient characteristics, nursing workload and outcome. Intensive Care Med 1997;23:1165-1170.
Chaix C, Durand-Zaleski I, Alberti C, et al: Control of endemic methicillin-resistant Staphylococcus aureus: a cost-benefit analysis in an intensive care unit. JAMA 1999;282:1745-1751.
Barakate MS, Yang Y-X, Foo S-H, et al: An epidemiological survey of methicillin-resistant Staphylococcus aureus in a tertiary referral hospital. J Hosp Infect 2000;44:19-26.
Samad A, Banerjee D, Carbarnes N, Ghosh S: Prevalence of methicillin-resistant Staphylococcus aureus colonization in surgical patients, on admission to a Welsh hospital. J Hosp Infect 2002;51:43-46.
Boyle-Vavra S, Ereshefsky SB, Wang CC, Daum RS: Successful multiresistant community-associated methicillin-resistant Staphylococcus aureus lineage from Taipei, Taiwan, that carries the novel staphylococcal chromosome cassette mec (SCCmec) type VT or SCCmec type IV. J Clin Microbiol 2005;43:4719-4730.
Chen FJ, Lauderdale TL, Huang IW, et al: Methicillin-resistant Staphylococcus aureus in Taiwan. Emerg Infect Dis 2005;11:1761-1763.
Ito T, Ma XX, Takeuchi F, et al: Novel type V staphylococcal chromosome cassette mec driven by a novel cassette chromosome recombinase, ccrc. Antimicob Agents Chemother 2004;48:2637-2651.
Clinical and Laboratory Standard Institute: Performance Standards for Antimicrobial Susceptibility Testing; 22nd Informational Supplement (32:M100-S22). Wayne, CLSI, 2012.
Udo EE, Farook VS, Mokadas EM, et al: Molecular fingerprinting of mupirocin-resistant Staphylococcus aureus from a burn unit. Int J Infect Dis 1999;3:82-87.
Goh S-H, Byrne SK, Zang JL, et al: Molecular typing of Staphylococcus aureus on the basis of coagulase gene polymorphisms. J Clin Microbiol 1992;30:1642-1645.
Oliveira DC, de Lencastre H: Multiplex PCR strategy for rapid identification of structural types and variants of the mec element in methicillin-resistant Staphylococcus aureus. Antimicrob Agents Chemother 2002;46:2155-2161.
Zhang K, McClure J-A, Elsayed S, et al: Novel multiplex PCR assay for characterization and concomitant subtyping of staphylococcal cassette chromosome mec types I to V in methicillin-resistant Staphylococcus aureus. J Clin Microbiol 2005;43:5026-5033.
Harmsen D, Claus H, Witte W, et al: Typing of methicillin-resistant Staphylococcus aureus in a university hospital setting by using novel software for spa repeat determination and database management. J Clin Microbiol 2003;41:5442-5448.
Enright MC, Day NP, Davies CE, et al: Multilocus sequence typing for characterization of methicillin-resistant and methicillin-susceptible clones of Staphylococcus aureus. J Clin Microbiol 2000;38:1008-1015.
Hardy KJ, Hawkey PM, Gao F, et al: Methicillin-resistant Staphylococcus aureus in the critically ill. Br J Anaesth 2004;92:121-130.
Hoefnagels-Schuermans A, Borremans A, Peetermans W, et al: Origin and transmission of methicillin-resistant Staphylococcus aureus in an endemic situation: differences between geriatric and intensive care patients. J Hosp Infect 1997;36:209-222.
Panhotra BR, Saxena AK, Al Mulhim AS: Prevalence of methicillin-resistant and methicillin-sensitive Staphylococcus aureus nasal colonization among patients at the time of admission to the hospital. Ann Saudi Med 2005;25:304-308.
Sarikonda KV, Micek ST, Doherty JA, et al: Methicillin-resistant Staphylococcus aureus nasal colonization is a poor predictor of intensive care unit-acquired methicillin-resistant Staphylococcus aureus infections requiring antibiotic treatment. Crit Care Med 2010;38:1991-1995.
Honda H, Krauss MJ, Coopersmith CM, et al: Staphylococcus aureus nasal colonization and subsequent infection in intensive care unit patients: does methicillin resistance matter? Infect Control Hosp Epidemiol 2010;31:584-591.
Korn GP, Martino MD, Mimica LJ, et al: High frequency of colonization and absence of identifiable risk factors for methicillin-resistant Staphylococcus aureus (MRSA) in intensive care units in Brazil. Braz J Infect Dis 2001;5:1-7.
Marshall C, Spelman D, Harrington G, et al: Daily hazard of acquisition of methicillin-resistant Staphylococcus aureus infection in the intensive care unit. Infect Control Hosp Epidemiol 2009;30:125-129.
Open Access License / Drug Dosage / Disclaimer
Open Access License: This is an Open Access article licensed under the terms of the Creative Commons Attribution-NonCommercial 3.0 Unported license (CC BY-NC) (www.karger.com/OA-license), applicable to the online version of the article only. Distribution permitted for non-commercial purposes only.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.