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Fighting the Resistance: Time to Rethink the Staphylococcus aureus Battle (RG Sawyer)
Posted in Lectures on 11 June 2019

Robert G Sawyer


Staphylococcus aureus is one of the most common pathogens responsible for surgical site infections and healthcare-associated infections (HAI) in general. It is associated with high morbidity and mortality rates in hospitalized patients. Methicillin-resistant Staphylococcus aureus (MRSA) has been the focus of many decontamination programs to prevent SSIs and other HAI, since its resistance pattern limits antibiotic treatment options. Methicillin-susceptible Staphylococcus aureus (MSSA), its multi-sensitive variation, is also associated with high morbidity and mortality rates and has been gradually growing in incidence and prevalence in recent years.

Dr. Robert Sawyer tried to show us if MSSA could somehow be more virulent and associated with higher mortality in hospitalized patients.


The study hypothesized that, if limited to Intensive Care Unit (ICU), acquired infections and controlling for major diagnostic groups and other factors, the mortality rates associated with MRSA and MSSA are similar.


The group conducted a retrospective analysis of a dataset prospectively collected at the University of Virginia from 1997 to 2017. Patients were mixed general surgery and trauma, and infections were only ICU-acquired. An univariant and multivariant analysis was performed with a priori chosen factors: age, APACHE II score, Trauma and non-Trauma diagnosis, days of in-hospital stay prior to the infection, ventilator dependence, and transfusion.


466 patients were included in the study, with 223 presenting with an MRSA infection and 223 with an MSSA infection. Patients with an MSSA infection tended to be younger (mean age 48) compared to, MRSA patients. Patients with MSSA also tended to be infected with the pathogen earlier and needed fewer days of antibiotic treatment.

The results showed a higher prevalence of MRSA infections in the first decade of the study, with and abrupt reduction in the beginning of 2000s, and a gradual and slow regrowth in the last decade. MSSA had a similar evolution but has become more prevalent than MRSA since 2015.


Staphylococcus aureus infections are very common causes of healthcare-associated morbidity and mortality. The epidemiology of S. aureus pathogens has been changing, and now we have  higher incidence and prevalence rates for MSSA infections than for MRSA. Although multi-sensitive, MSSA is associated with high morbidity and mortality rates, is in-hospital acquired, and can occur earlier during the patient’s stay.

In the future, we should focus on the prevention and treatment of all S. aureus infections.