Antimicrobial susceptibility patterns of Staphylococcus aureus in a tertiary referral hospital in Nairobi, Kenya

Staphylococcus aureus is a leading cause of hospital and community acquired infections globally. Methicillin-resistant S. aureus (MRSA) prevalence has been reported to be high in various settings and is associated with increased morbidity, mortality and risk of nosocomial outbreaks. Surveillance of prevalence and antibiotic susceptibility patterns is important to ensure appropriate antibiotic prescription. The objective of our study was to establish the prevalence of S. aureus, to identify patterns of susceptibility to commonly used antibiotics and quantify contemporary penicillin resistance among S. aureus. A retrospective study was conducted at the Mater Hospital, Nairobi. The study involved a review of non-duplicate records of specimens analyzed between January 2014 and December 2018. An isolate was categorized as Penicillin susceptible (PSSA) if it was susceptible to Penicillin and Oxacillin, Methicillin susceptible (MSSA) if resistant to Penicillin but susceptible to Oxacillin and Methicillin resistant (MRSA) if resistant to Oxacillin and Penicillin. We present proportions of S. aureus that was PSSA, MSSA and MRSA. Multivariate logistic regression was used to determine the association between the presence of S. aureus isolates and the source of the clinical specimen (inpatient vs. outpatient), age and gender. A total of 659 isolates of S. aureus were analyzed in 5-year period. PSSA was the most prevalent organism seen (60.85%) while MRSA was the least prevalent (0.61%). Most S. aureus were isolated in pus from wound swabs-644 (73. 3%). A significant increase in susceptibility of S. aureus to Penicillin and Amoxicillin-clavulanic acid was observed during the study period. This study demonstrated a high prevalence of Penicillin Sensitive S. aureus and a low prevalence of MRSA. Key words: Staphylococcus aureus, antimicrobial, penicillin.