Nasal carriage of methicillin resistant Staphylococcus aureus among health care workers at a tertiary care hospital in Western Nepal

Background Staphylococcus aureus is a frequent cause of infections in both the community and hospital. Methicillin-resistant Staphylococcus aureus continues to be an important nosocomial pathogen and infections are often difficult to manage due to its resistance to multiple antibiotics. Healthcare workers are important source of nosocomial transmission of MRSA. This study aimed to determine the nasal carriage rate of S. aureus and MRSA among healthcare workers at Universal College of Medical Sciences and Teaching Hospital, Nepal and to determine antibiotic susceptibility pattern of the isolates. Methods A cross-sectional study involving 204 healthcare workers was conducted. Nasal swabs were collected and cultured on Mannitol salt agar. Mannitol fermenting colonies which were gram positive cocci, catalase positive and coagulase positive were identified as S. aureus. Antibiotic susceptibility test was performed by modified Kirby-Bauer disc diffusion method. Methicillin resistance was detected using cefoxitin disc diffusion method. Results Of 204 healthcare workers, 32 (15.7 %) were nasal carriers of S. aureus and among them 7 (21.9 %) were carrier of MRSA. Overall nasal carriage rate of MRSA was 3.4 % (7/204). Highest MRSA nasal carriage rate of 7.8 % (4/51) was found among nurses. Healthcare workers of both surgical wards and operating room accounted for 28.6 % (2/7) of MRSA carriers each. Among MRSA isolates inducible clindamycin resistance was observed in 66.7 % (2/3) of erythromycin resistant isolates. Conclusions High nasal carriage of S. aureus and MRSA among healthcare workers (especially in surgery ward and operating room) necessitates improved infection control measures to be employed to control MRSA transmission in our setting.


Background
Staphylococcus aureus is a frequent cause of infections in both the community and hospital. The Methicillinresistant S. aureus (MRSA) has emerged as one of the commonest causes of hospital acquired infection and continues to remain an important factor contributing to failure of management [1]. MRSA strains are not only a problem in hospital as distinct strains have emerged in community too, which are referred to as Community acquired MRSA (CA-MRSA). CA-MRSA strains have spread in community settings and have also entered healthcare facilities [2].
Healthcare workers (HCWs) who are at interface between the hospital and the community may serve as agents of cross contamination of Hospital acquired MRSA (HA-MRSA) and CA-MRSA [3]. HCWs are the source of nosocomial transmission of MRSA in developing countries [4,5]. The average nasal carriage rate of S. aureus and MRSA among HCWs has been shown to be 23.7 and 4.6 % respectively [3]. Different studies from Nepal have showed nasal carriage rate of S. aurues among HCWs to be 20.37 -43.8 % [6][7][8][9].
Identification of patients and HCWs in outbreak settings colonized with MRSA combined with hand hygiene and other precautions have been shown to be effective in reducing the transmission and controlling the spread of MRSA. This study was undertaken to investigate the nasal carriage rate of S. aureus and MRSA among HCWs at our hospitals and to determine antibiotic susceptibility pattern of the isolates.

Methods
This cross sectional study was carried out at Universal College of Medical Sciences and Teaching Hospital, Bhairahawa, Nepal during the period of November -December 2013. The study was approved by institutional review committee of Universal College of Medical Sciences, Bhairahawa, Nepal. Informed consent was taken from all the participants. Nasal swabs from 204 HCWs were collected before commencement of duties. HCWs with history of upper respiratory tract infection, fever, recent nasal surgery, diabetes, immunocompromisation, use of nasal medications, or antimicrobial therapy were excluded. Nasal swabs were collected from anterior nares of the HCWs using sterile cotton swabs (moistened with normal saline). The swab was introduced 2-3 cm in the nasal cavity and rotated 4-5 times both clockwise and anticlockwise. The swabs were then immediately transported to the Microbiology laboratory for further processing. Specimens were inoculated onto Mannitol salt agar (MSA) and incubated at 37°C for 48 h. Mannitol fermenting colonies that were yellow or golden yellow were selected and sub-cultured on Nutrient agar (NA). Colonies on NA were subjected to Gram's staining, catalase test and coagulase test. Gram positive cocci that were catalase positive and coagulase positive were identified as S. aureus [10]. Antibiotic susceptibility testing of all isolates was performed by modified Kirby Bauer disc diffusion method as recommended by CLSI guidelines [11]. The antibiotics used in the study were amikacin (30 μg), ceftriaxone (30 μg), cefoxitin (30 μg), ciprofloxacin (5 μg), cloxacillin (30 μg), clindamycin (2 μg), cotrimoxazole (1.25/23.75 μg), erythromycin (15 μg), gentamycin (10 μg), penicillin (10Units), teicoplanin (30 μg), tetracycline (30 μg) and vancomycin (30 μg). Inducible clindamycin resistance was detected by D-test. Methicillin resistance was detected using cefoxitin disc diffusion test. [11] Data was analyzed using SPSS 17.0.

Discussion
This study detected a nasal carriage rate of S. aureus to be 15.7 % among HCWs which is lower than that reported by studies from elsewhere in Nepal; 20.37-43.80 % [6][7][8][9]. This is also lower than that reported (19.80-48 %) internationally [12][13][14][15][16][17][18] [4]. This may also be a possible cause of low MRSA prevalence in this study. On the other hand, MRSA carriage rate among HCWs is higher in this study as compared to the studies among US population (1.5 %) [23] and that among community adults in the other countries (0.8 to 3.0 %) [24][25][26] indicating the possibility of hospital acquired MRSA colonization among HCWs. S. aureus carriage rate was highest among doctors (20.8 %) whereas MRSA carriage rate was highest among nurses (7.8 %) in this study. Similar results have been reported by Shibabaw et al. [27]. High risk of colonization with MRSA strains among nurses may be due to their frequent patient contact. HCWs from surgical ward and operating room accounted for 28.6 % of the MRSA carriers each. Similar findings were reported from others studies [28,29]. This could be due to the traumatic and postoperative immunological suppression of the patients [29]. The nasal carriage of MRSA among HCWs has indicated the chances of transmission of the organism to patients during patient-care. As most isolates belonged to HCWs from surgical ward and operating room, the vulnerability of surgical wound infection with MRSA among the patients, following transmission from the HCWs, further complicating the treatment and recovery, cannot be ignored. Detection of MRSA among HWCs at emergency ward possibly indicates incursion of CA-MRSA into hospital setting, however this has to be  confirmed by typing of the strain. The emergency department is a site of high healthcare worker-patient contact, high patient turnover, potentially substantial crowding, and many infected patient wounds that are being drained, explored, and dressed; perhaps it is these characteristics of the emergency department, along with the emergence of CA-MRSA infections in this setting, that explain the colonization observed among HCW in emergency department [30]. The susceptibility testing of MRSA isolates revealed high resistance towards gentamycin and erythromycin (42.9 % each). Low resistance towards ciprofloxacin (14.3 %) and cotrimoxazole (28.6 %) indicates these antibiotics might be an option for empirical therapy of MRSA infections at our hospital. Clindamycin resistance (14.3 %) was also low; however, iMLS B phenotype was seen in 66.7 % of erythromycin resistant MRSA isolates. Though lower resistance of isolates to clindamycin suggests it can be considered for empirical therapy, testing for the detection of inducible clindamycin resistance should be routinely performed in view of high iMLS B phenotype detected among MRSA isolates.

Conclusion
This study revealed that the prevalence of nasal carriage of S. aureus and MRSA among HCWs was low compared to other studies in our country and internationally. The carriage rate of S. aureus and MRSA is highest among doctors and nurses respectively. The MRSA carriage rate is high among the HCWs of surgical ward and operating room at our hospital. Inducible clindamycin resistance is high among MRSA isolates. Nasal carriage of S. aureus and MRSA among HCWs necessitates the need of control in the frequency of their exposure with the vulnerable patients. The basic infection control measures, screening program and treatment of MRSA-positive HCWs can help as an effective measure to control MRSA infections.