Resistant Staphylococcus aureus Causing Community-acquired Pneumonia Needs Novel Diagnostics Strategy, Study Shows

Resistant Staphylococcus aureus Causing Community-acquired Pneumonia Needs Novel Diagnostics Strategy, Study Shows

In a new study, researchers highlighted the need for new diagnostic strategies to effectively distinguish between susceptible and resistant Staphylococcus aureus causing community-acquired pneumonia (CAP), so that effective antibiotic therapies are properly prescribed to patients. The study “Staphylococcus aureus Community-acquired Pneumonia: Prevalence, Clinical Characteristics, and Outcomes” was published in the advanced online section of Clinical Infectious Diseases journal.

CAP caused by Staphylococcus aureus is an emergency condition; especially when the disease is caused by a resistant strain, the methicillin-resistant S. aureus (MRSA), which leads to severe pneumonia and culminates in patient death.

Recent studies suggested that in the United States, MRSA is an uncommon cause of CAP. However, in the clinic, two antibiotics – vancomycin and linezolid – are the preferable choice to treat adults with CAP, due to concerns about the potential of MRSA pneumonia. While the use of anti-MRSA antibiotics for CAP is not routinely advised, in the cases where MRSA pneumonia is clinically suspected, it is recommended to add vancomycin or linezolid to standard therapy.

In order to properly prescribe appropriate treatment, it is essential to identify and distinguish the clinical syndrome of MRSA CAP from other types of CAP. The clinical features associated with MRSA CAP previously detected included hemodialysis, influenza infection, hemoptysis, multifocal or cavitary infiltrates. These associations have not been independently evaluated.

In this new study, a team of researchers estimated the prevalence of MRSA and methicillin-susceptible S. aureus (MSSA) in a multicenter prospective surveillance study of adults hospitalized with CAP. The authors also compared several parameters (epidemiologic, radiographic, and clinical) of S. aureus CAP with pneumococcal CAP (S. pneumoniae is the most common cause of community-acquired pneumonia).

In total, from a pool of 2,259 adults hospitalized for CAP, 1.6% (37 patients) were positive for S. aureus, including 0.7% (15 patients) with MRSA and 1.0% (22 patients) with MSSA, and 5.1% (115 patients) had S. pneumonia. In the first three days of hospitalization, vancomycin or linezolid was administered to 674 (29.8%) patients. While patients with MRSA exhibited a 20% prevalence of chronic hemodialysis, only 2.6% of pneumococcal and all-cause non-S. aureus (3.7%) CAP registered this symptom. Hence, chronic hemodialysis is particularly more common in MRSA patients. Other clinical parameters at admission, including concurrent influenza infection, hemoptysis, multilobar infiltrates, and pre-hospital antibiotics remained the same in all groups of patients.

In conclusion, researchers noted that although MRSA CAP has a low prevalence in these patients (accounting for < 1% of hospitalized CAP cases), the initial clinical manifestations of MRSA and MSSA CAP overlapped substantially not only with one another, but also with all-cause non-S. aureus CAP (in particular with CAP caused by S. pneumonia). Moreover, despite this factor, nearly one-third of adults hospitalized with CAP received anti-MRSA antibiotics.

Unfortunately, the overlapping symptomatic between MRSA CAP and pneumococcal CAP suggest that the development of an efficient clinical prediction model to accurately identify MRSA CAP at hospital admission is a challenge.

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