Prevalence of Methicillin Resistant Staphylococcus aureus Nasal Colonizers among Basic Science MBBS and BDS Students of Kathmandu Medical College

ABSTRACT Introduction: Methicillin-Resistant Staphylococcus aureus exhibit multiple drug resistance phenotypes. Colonizers harboring Methicillin-Resistant Staphylococcus aureus are often associated with its outbreaks in both hospital and community settings. This study was done to determine the prevalence of nasal carriage rate of Methicillin-Resistant Staphylococcus aureus among basic science MBBS and BDS students of Kathmandu Medical College. Methods: A descriptive cross-sectional study was done in Kathmandu Medical College from March 5 to June 5 2020. Ethical clearance was obtained from the Institutional Review Committee with reference no. 040320201. A convenient sampling method was used, and the sample size was calculated with a prevalence of 50%. Two hundred students studying MBBS and BDS were enrolled. The nasal swab was collected and processed using standard microbiological methods. The data obtained were computed and analyzed using Statistical Package for Social Sciences 16.0 Version. Results: Among 200 participants, 9 (4.5%) were found to be nasal carriers of Methicillin-Resistant Staphylococcus aureus. Conclusions: Colonization of anterior nares by Methicillin-Resistant Staphylococcus aureus in apparently healthy individuals is a cause of concern. Education regarding Methicillin-Resistant Staphylococcus aureus, its carrier and significance, and its screening must be included early on in MBBS and BDS.


INTRODUCTION
Methicillin-resistant Staphylococcus aureus (MRSA), once confined mainly to healthcare-associated infections, has been increasingly reported from community. 1 The hospital-associated MRSA (HA-MRSA) is generally associated with patients with predisposing factors such as prolonged hospitalization, use of indwelling catheters, or prior surgical procedures. In contrast, community-associated MRSA (CA-MRSA) is associated with healthy and younger people without such predisposing factors. 2 It has been identified that nasal colonization of S. aureus plays a key role in its pathogenesis. 3 MRSA isolates exhibit multidrug resistance; moreover, increasing reports of MRSA isolates with decreased susceptibility to glycopeptides (glycopeptide intermediately susceptible S. aureus, GISA) is a cause for great public concern. 4 In this study, we aimed to ascertain the prevalence of nasal colonization rate of MRSA among healthy basic science MBBS and BDS students of Kathmandu Medical College.

METHODS
A descriptive cross-sectional study was done in Kathmandu Medical College from 5 th March to 5 th June, 2020. Ethical clearance was obtained from the Institutional Review Committee with reference no.

on Mar 4 2020.
A descriptive cross-sectional study was done in 200 students. Convenient sampling method was used and the sample size (n) was calculated with prevalence of 50% as follows: n = Z² x p x q/e² = 1.96² x 0.5 x (1-0.5)/0.07² = 196 Where, Z= 1.96 for 95% confidence interval p= prevalence (50%) q= 1-p e= margin of error= 7% n= minimum number of the sample size required Two hundred undergraduate students studying in the first and second years of MBBS and BDS and willing to participate in the study were enrolled. Written consent was taken from the participants. A Performa was designed to verify associated risk factors like history of skin infection (organism associated, recurrence), recent hospital admission, OPD visit, recent antibiotic usage.
For microbiological confirmation of S. aureus colonization followed by the MRSA detection, the nasal swab was collected from anterior nares of the participants using sterile swab sticks and inoculated onto Mannitol salt agar. Yellow colonies yielded on Mannitol salt agar were preliminarily identified as S. aureus. Further confirmation was done using Gram's stain, Catalase, and Coagulase test using standard Microbiological techniques.
Antibiotic susceptibility testing of the S. aureus isolates was done using a modified Kirby-Bauer disc diffusion method. 5 MRSA detection was done using cefoxitin (30µg) disc following the modified Kirby-Bauer disc diffusion technique. The S. aureus isolates exhibiting ≤21 mm of inhibition zone around the cefoxitin disk were confirmed as MRSA. Reference strains S. aureus ATCC 25923 and ATCC 43300 were used as negative and positive controls, respectively. 6 The data obtained were computed and analyzed using SPSS 16.0 Version.

RESULTS
A total of 200 participants were enrolled in the study. All the participants were in the age group of 18-25 years. Among the participants, 9 (4.5%) participants were found to be harboring MRSA.
Among the participants with MRSA colonization, associated risk factors were observed. However, 4 (44.44%) of the colonizers did not have a history of any associated risk factors (Table 1). The Antimicrobial susceptibility testing of the MRSA isolates showed the highest antibiotic resistance prevalence against Ceftriaxone 9 (100%) (Figure 1).

DISCUSSION
Nasal carriage of MRSA in colonized persons acts as a potential endogenous reservoir for clinical infections and a cross-colonization source for the spread in community. 7 Medical students, though overlooked, could be a significant potential source of infection in healthcare settings.
In our study, a total of 200 participants studying in the first and second year of MBBS and BDS were enrolled for the study. The study's limitations were that intermittent carriers may have been missed as the study was crosssectional, and only one method of screening MRSA was used. Moreover, detail follows up of the students regarding their knowledge regarding MRSA was not done. Molecular characterization of MRSA was not done due to resource constraints.

CONCLUSIONS
The nasal carriage of MRSA by apparently healthy medical and dental students may inadvertently play a role in changing the epidemiology of MRSA in healthcare settings. Preventive measures and educating the students is needed to avoid outbreaks.