Empirical anti-MRSA antibiotics may not benefit patients with pneumonia

Adding empirical anti-methicillin-resistant Staphylococcus aureus (MRSA) therapy to standard antibiotic regimens in patients hospitalized for pneumonia is associated with an elevated risk of 30-day all-cause mortality, a recent retrospective study found.

“[W]e were unable to establish benefit of empirical anti-MRSA therapy, even when risk factors for MRSA were present or clinical severity warranted admission to the intensive care unit (ICU),” said the researchers.

“Our study calls into question the strategy of broad empiric antibiotic coverage that has previously been promoted by pneumonia practice guidelines,” said lead author Assistant Professor Barbara Jones from the Veterans Affairs (VA) Salt Lake City Health Care System, Salt Lake City, Utah, US.

Researchers utilized data from the Veterans Health Administration to identify 88,605 patients (median age 70 years, 2 percent female) who were prescribed standard empirical antibiotic regimens (β-lactam and macrolide or tetracycline hydrochloride, or fluoroquinolone) with or without empirical anti-MRSA therapy (vancomycin hydrochloride [98 percent in this study] or linezolid) upon hospitalization (day 1) for community-onset pneumonia between 2008 and 2013.

Thirty-eight percent of patients (n=33,632) received empirical anti-MRSA therapy, of whom 20,104 received empirical anti-MRSA therapy alone and 13,528 in addition to standard antibiotics. A total of 8,929 deaths were recorded at 30 days.

Compared with standard therapy alone, 30-day all-cause mortality was significantly higher with empirical anti-MRSA therapy plus standard therapy (adjusted risk ratio [adjRR], 1.4, 95 percent CI, 1.3–1.5), as well as with empirical anti-MRSA therapy alone (adjRR, 1.5, 95 percent CI, 1.4–1.6). [JAMA Intern Med 2020;doi:10.1001/jamainternmed.2019.7495]

The elevated mortality risk with anti-MRSA plus standard therapy persisted in subgroup analyses of patients with a clinical risk for MRSA (adjRR, 1.2), those initially admitted to the ICU (adjRR, 1.3), and those with nasal PCR*-detected MRSA (adjRR, 1.6), but not among the 2 percent of patients with culture-detected MRSA (adjRR, 1.1).

Empirical anti-MRSA therapy was also associated with elevated risks of kidney injury (adjRR, 1.4), Clostridioides difficile infection (adjRR, 1.6), vancomycin-resistant Enterococcus species (adjRR, 1.6), and secondary gram-negative rod detection (adjRR, 1.5). When analysed separately from anti-MRSA therapy, antipseudomonal therapy (adjRR, 1.3) and anti-MRSA therapy (adjRR, 1.2) were both associated with 30-day mortality risk.

The researchers noted that the isolation of MRSA cultures from sputum may present a limitation. “[R]espiratory cultures may have poor positive predictive value for MRSA pneumonia [and this] calls into question whether respiratory cultures should be used as a criterion standard for infection in pneumonia and adds urgency to the need for better diagnostic tools to more precisely identify bacterial and viral causes of pneumonia and other infections,” they said.

“Sometimes in our eagerness to improve outcomes, particularly among critically ill patients, we, as doctors, may be overly broad in our initial treatments,” noted senior author Professor Matthew Samore, also from the VA Salt Lake City Health Care System.

“We’re not saying that it’s never appropriate to use anti-MRSA therapy for treating pneumonia. But in the absence of better tests to identify MRSA as a potential pathogen causing the disease, using anti-MRSA therapies does not seem to offer any advantage over standard treatment therapy. Under these circumstances, it may be safer for patients if physicians stick to standard antibiotic treatments for a couple of days to see how patients are doing rather than leaping into anti-MRSA therapy right off the bat,” added Jones.