Predictive Value of Mrsa Nasal Swab in Patients with Covid-19 and Secondary Bacterial Pneumonia

ABSTRACT

INTRODUCTION: Secondary bacterial pneumonia in patients with COVID-19 is a severe complication. It has been noted that the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) positive respiratory cultures in patients with COVID-19 is approximately 6%. However, the true prevalence of bacterial co-infection in these patients is unknown. However, we do not know if infection with the SARS-COV-2 virus or the development of COVID-19 impacts the performance of the MRSA nasal swab screening test. Thus, we conducted a retrospective cohort study evaluating the predictive value of MRSA screening swabs in patients with COVID-19 and secondary bacterial pneumonia. METHOD(S) This was an IRB-approved, retrospective cohort study of patients who had nasopharyngeal specimens positive for SARS-COV-2 virus, screening MRSA nasal swabs performed, and bacterial cultures collected. Patients were diagnosed with pneumonia based on a standardized definition. The primary objective of this study was to determine the sensitivity, specificity, positive predictive value, and negative predictive value of a positive MRSA nasal swab and MRSA pneumonia in patients who are also positive for the SARS-COV-2 virus. Secondary outcomes included hospital length of stay, in-hospital mortality, and antibiotic therapies. RESULT(S) A total of 293 patients were included in the final analysis and 662 microbiological samples were evaluated in this study. The specificity (91.8% [95% CI 88.6% to 95%]) and negative predictive values (NPV 97.4% [95% CI 95.4% - 99.3%]) of MRSA nasal swabs were high. However, the sensitivity (46.2%;95% CI 19.1% to 73.3%) and positive predictive value (PPV 20.7%;95% CI 59.5 - 35.4%) were low. Those patients with a negative MRSA nasal swab had a median length of stay of 14 days (IQR 6 days to 26 days) and those with a positive nasal swab had a median length of stay of 20 days (IQR 12 days to 28 days) (p=0.096). There was no difference in in-hospital mortality. CONCLUSION(S) In general, screening MRSA swabs in patients with COIVD-19 had a high NPV and low positive PPV. Thus, the performance of screening MRSA swabs in patients with COIVD-19 and secondary bacterial pneumonia was similar to those patients without COVID-19.