Likely False-Positive Pneumococcal Antigen Test BinaxNOW Due to Parvimonas micra: A Four-Case Series

Area of Science:

• Microbiology
• Infectious Diseases
• Clinical Diagnostics

Background:

• Pleural empyema can be challenging to diagnose, especially in patients with risk factors for aspiration pneumonia.
• The BinaxNOW pneumococcal antigen test (PATB) is a rapid diagnostic tool used to detect Streptococcus pneumoniae in pleural fluid.
• Accurate diagnosis is crucial for appropriate antibiotic selection and patient management.

Observation:

• Four cases of nonpneumococcal pleural empyema were identified in patients with aspiration pneumonia risk factors.
• These patients exhibited false-positive results on the pneumococcal antigen test (PATB) performed on pleural fluid.
• All patients presented with polymicrobial infections, including Parvimonas micra and Fusobacterium nucleatum.

Findings:

• Cultures and PCR testing were negative for Streptococcus pneumoniae in all cases.
• Isolates from pleural fluid, including Parvimonas micra, were tested to investigate cross-reactivity with the PATB.
• The study identified a previously unrecognized cross-reactivity of the PATB with Parvimonas micra, leading to false-positive results.

Implications:

• Positive PATB results in patients with aspiration pneumonia risk factors should be interpreted with caution.
• The presence of anaerobic bacteria, such as Parvimonas micra, can cause false-positive PATB results.
• This finding necessitates a re-evaluation of diagnostic strategies for pleural empyema in at-risk populations.