Prevalence and Factors Associated With Staphylococcus Aureus Nasal Colonisation in Orthopaedic Patients

Abstract

Background: Staphylococcus aureus (S. aureus) is a Gram-positive aerobic bacterium. It can be found as part of a person’s normal bacterial flora i.e. these individuals (carriers) are asymptomatically colonised without evidence of staphylococcal disease. S. aureus is an important organism in orthopaedic practice as it is the most common cause of orthopaedic infections including surgical site infections (SSIs), osteomyelitis and septic arthritis. Carriers of S. aureus are predisposed to developing invasive staphylococcal infections. This is of concern as S. aureus has developed mechanisms of evading the immune system and resisting antimicrobials. Knowledge of a patient’s carrier status before surgery together with interventions to eliminate the carrier state have been shown to reduce post-operative infections by both methicillin sensitive Staphylococcus aureus (MSSA) and methicillin resistant Staphylococcus aureus (MRSA) Study Objective: To determine the prevalence and factors associated with colonisation by Staphylococcus aureus among patients who have been admitted to the orthopaedic wards at Kenyatta National Hospital (KNH) to undergo surgery and to determine the antibiotic susceptibility of Staphylococcal aureus found to be colonizing the anterior nares of patients Study Design: Cross-sectional study Study Setting: Kenyatta National Hospital orthopaedic clinics and wards as well as accident and emergency department from 1 June 2019 – 30 September 2019. Methodology: Consecutive sampling of patients based on the defined inclusion criteria was done until the required sample size was achieved. Nasal swabs were taken from patients at admission for culture and sensitivity. Data concerning comorbid conditions as well as healthcare associated risk factors was collected. Demographic characteristics were summarized and presented as frequencies and proportions for categorical variables, and as means with standard deviations for continuous variables. The prevalence of nasal colonisation by Staphylococcus aureus (both MRSA and MSSA) among orthopaedic patients was analysed and presented as a proportion of the sample size. The antibiotic susceptibility pattern of Staphylococcus aureus strains was analysed and presented as frequencies and proportions. The risk factors and socio demographic characteristics were analysed at univariate and multivariate with the use of Chi square tests. Odds ratio as well as 95% confidence intervals were calculated. A p-value < 0.05 was considered significant. Data Processing: The collected data was analysed using the Statistical Package for the Social Sciences version 25. Results: The overall prevalence of colonisation by Staphylococcus aureus at admission was found to be 24.7% whereas the overall prevalence of colonisation by Methicillin Resistant Staphylococcus aureus (MRSA) was found to be 3.03%. Conclusion: The prevalence of colonisation by Staphylococcus aureus is high amongst patients being admitted to orthopaedic wards at Kenyatta National Hospital when compared to previous studies and amongst these are those who are colonised by MRSA. The prevalence of MRSA, its resistance to commonly used antibiotics and the association of colonisation by Staphylococcus aureus predisposing to infection call for the need of screening programmes to curtail spread within hospital and community settings.