Researchers examined the true prevalence of methicillin (antibiotic)-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in the context of community-acquired pneumonia (CAP) — and how the current guidelines affect clinical and antibiotic-selection decisions.
The findings highlight that, despite a very low prevalence of MRSA community-acquired pneumonia, many adults hospitalized with it were unnecessarily given anti-MRSA antibiotics. New diagnostic strategies are urgently needed, the study said.
The research paper, titled “Staphylococcus aureus Community-acquired Pneumonia: Prevalence, Clinical Characteristics, and Outcomes,” was published in Clinical Infectious Diseases.
The routine use of anti-MRSA antibiotics is of great concern due to the significance and spread of bacterial strains that do not respond to current clinical treatments.
Such practices are not recommended in the current CAP consensus guidelines of the Infectious Diseases Society of America and the American Thoracic Society. However, the accurate prevalence of CAP, caused by S. aureus, and its clinical features remain poorly described, which in turn complicates the selection of antibiotics in a clinical setting.
In this study, researchers conducted a multicenter prospective study with 2,259 adults hospitalized with CAP, comparing the epidemiologic, radiographic, and clinical characteristics of S. aureus CAP with those of pneumococcal and non-S.aureus CAP.
Among this patient population, 37 people (1.6 percent) tested positive for S. aureus, including 15 (0.7 percent) with MRSA and 22 (1.0 percent) with MSSA. A total of 115 patients had pneumococcal disease (infection with Streptococcus pneumoniae).
Patients with MRSA CAP had more severe clinical outcomes than those with pneumococcal CAP, such as intensive care unit admission (86.7 percent vs. 34.8 percent) and in-patient mortality (13.3 percent vs. 4.4 percent).
Despite the low incidence of MRSA pneumonia, vancomycin or linezolid, anti-MRSA antibiotics were given to 674 (29.8 percent) CAP-hospitalized patients within the first three days of hospitalization.
The lack of distinctive clinical features especially between MRSA CAP and pneumococcal CAP, makes it very difficult for clinicians to accurately select anti-MRSA antibiotics only when necessary. As such, there is a real need for rapid and accurate diagnostic tests that would allow the confirmation of MRSA CAP.
“The clinical presentation of MRSA CAP overlapped substantially with pneumococcal CAP, highlighting the challenge of accurately targeting empirical anti-MRSA antibiotics with currently available clinical tools and the need for new diagnostic strategies,” the researchers said in their final remarks.