Value of bacterial antigen detection in the diagnostic yield of transthoracic needle aspiration in severe community acquired pneumonia.

BACKGROUND Transthoracic needle aspiration (TNA) with an ultrathin needle is a safe and highly specific procedure for obtaining a diagnosis in bacterial pneumonias, but its sensitivity is at best 70%. A study was performed to assess whether Streptococcus pneumoniae and Haemophilus influenzae type b antigen detection by latex agglutination from the TNA sample enhanced the diagnostic yield. METHODS Blood cultures, TNA with an ultrathin needle (culture, Gram stain, and latex agglutination), serological tests, and pneumococcal antigen detection in the urine by counterimmunoelectrophoresis were performed in samples from 18 of 23 consecutive patients with severe community acquired pneumonia. RESULTS The causative organism was identified in 16 cases (88%): S pneumoniae (10 cases), S pneumoniae plus H influenzae (two cases), Legionella pneumophila (three cases), and Mycoplasma pneumoniae (one case). The investigation of antigens by latex agglutination in the pulmonary aspirate increased the diagnostic yield of TNA from 50% to 78% and provided a rapid diagnosis (in less than two hours) with therapeutic implications in seven cases. Its effectiveness was not modified by prior antibiotic therapy. CONCLUSIONS A latex agglutination test on the pulmonary aspirate enhances the diagnostic yield of TNA in severe community acquired pneumonia.