Prevalence and antimicrobial susceptibility pattern of Staphylococcus Aureus isolated from clinical specimens at the Mater Hospital Nairobi, Kenya.

Abstract Background Staphylococcus aureus is a leading cause of hospital and community acquired infections globally. Surveillance of prevalence and antibiotic susceptibility patterns is important to ensure appropriate antibiotic prescription. The aim of this study was to determine the prevalence and susceptibility patterns of Staphylococcus aureus isolated from clinical specimens in a tertiary hospital with diverse and empirical prescribing habits. Methods A retrospective study was conducted at the Mater Misericordiae Hospital, Nairobi. The study involved records of specimens analyzed between January 2014 and December 2018. S aureus was identified using catalase and coagulase tests. Strains phenotypically resistant to <3 non β-lactam antimicrobial categories were defined as non-multidrug-resistant MRSA (nmMRSA) and strains that were resistant to ≥3 non-β-lactam antimicrobial groups were defined as multidrug-resistant MRSA (mMRSA). A specimen was categorized as Penicillin susceptible (PSSA) if susceptible to penicillin and oxacillin, MSSA if resistant to penicillin and susceptible to oxacillin, and MRSA if resistant to oxacillin and penicillin. Isolates were screened for MRSA using 6μg/ml of oxacillin disc in Mueller-Hinton agar supplemented with 4%NaCl.Data was analyzed using Statistical Package for Social Sciences(SPSS) version 20 software. Pearson’s chi square and Logistic regression were used to assess association between dependent and independent variables. Results A total of 890 specimens of S. aureus were analyzed in the 5-year period. ​​PSSA was the most prevalent organism seen (45%) while MRSA was the least prevalent (0.45% ). There was a fluctuation in the annual prevalence of MRSA between 0-1% over the five years. Most S. aureus was isolated in pus-644(73. 3%). A significant increase in susceptibility of S. aureus to Penicillin and Amoxicillin-clavulanic acid was observed during the study period however, sensitivity to Amoxicillin declined. No mMrsa was detected. Resistance of MRSA to Ampicillin, Penicillin, Tazopiperacillin, Cephalosporins, Erythromycin, Clindamycin, Ciprofloxacin and Meropenem was 100% with both Trimethoprim/sulfamethoxazole and Levofloxacin recording 50% and amoxicillin/clavulanic acid 75% resistance. Conclusion This study demonstrated a steady decline in average annual resistance of S. aureus to commonly used antibiotics. Furthermore, there was a low prevalence of MRSA. No multi-drug Methicillin resistant S. aureus have been isolated in the last five years in this hospital.