Detection of Methicillin-resistant Staphylococcus Aureus in Clinical Samples at Kenyatta National Hospital Using Phenotypic and Molecular Methods

Abstract

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a global problem with a prevalence of between 29 and 35% reported worldwide. There is great variation in the epidemiology of MRSA at global and regional levels. Locally the reason for the variation in reported prevalence has been attributed to a lack of standardized methods for the detection of MRSA with some facilities using nonspecific methods such as coagulase to confirm S. aureus. This study aims to compare the diagnostic accuracy of the Vitek-2 system with the cefoxitin disc test in the detection of MRSA prevalence at Kenyatta National Hospital in Kenya using PCR as the gold standard. Methods: A cross-sectional study design was used where all non-duplicate Staphylococcus aureus isolates from various specimen types from patients at Kenyatta National Hospital were collected. S. aureus isolate purity was ascertained by subculture before they were identified and tested for their sensitivity to various antibiotics according to Clinical Laboratory Standards Institute (CLSI) guidelines using the Vitek-2 System. MRSA isolates were confirmed using cefoxitin disc diffusion and GenoType MRSA PCR method for the detection of the mecA or mecC gene. Data on antibiotic sensitivity testing obtained from the Vitek-2 database was entered into WHONET software where it was analyzed and presented in tables and charts. Minimum inhibitory concentration (MIC) of > = 22mm was interpreted as methicillin-resistant (MRSA) while MIC of < =21 was interpreted as methicillin-susceptible (MSSA). Results: A total of 418 nonduplicate S. aureus isolates were collected between October 2019 and December 2020. Out of these, 239 (146 MRSA and 93 MSSA) S. aureus isolates were randomly selected for molecular detection for the presence of mecA, mecC, and pvl genes. MRSA prevalence was 49 % (206/418), while 39 % (93/418) harbored the pvl gene. mecC gene was not detected. Comparative MRSA detection with cefoxitin disc diffusion test, Vitek-2 system, and GenoType MRSA showed perfect categorical agreement. The highest MRSA prevalence was noted in the pediatrics department at 52.5%, followed by surgical (50%) and medicine departments (49.3%). Less than 20% of the MRSA isolates were resistant to tetracycline, erythromycin, and sulfamethoxazole/trimethoprim. All MRSA isolates were sensitive to teicoplanin, linezolid, and vancomycin. Conclusions: The prevalence of MRSA in Kenyatta National Hospital is high (49.2%) when weighed against a global prevalence of 29% to 35%. The presence of pvl-positive MRSA in the hospital setup is a concern considering it can cause serious disease outbreaks. The Cefoxitin disc test can be used as a cheap alternative for screening MRSA, especially oxacillin-sensitive phenotype. However, creating an algorithm to complement the Vitek-2 system for confirming MRSA can be a valuable addition to ensure accurate identification.