Could the Streptococcus pneumoniae immunochromatographic test applied to nasopharyngeal aspirate be useful for diagnosing pneumococcal pneumonia?

Abstract number: P1152

Athlin S., Strålin K.

Objectives: In order to facilitate early diagnosis of community-acquired pneumonia (CAP) caused by Streptococcus pneumoniae we evaluated the rapid immunochromatographic membrane test (Binax NOW Streptococcus pneumoniae kit; ICT) on nasopharyngeal aspirates (NpAs). The test is validated on urine and cerebrospinal fluid according to the manufacturer.

Methods: In this prospective study samples were collected from 193 adults hospitalised for CAP and 64 adults with no infection as controls. ICT was applied to NpAs, which had been collected with an electronic suction device. Blood culture, urinary antigen test and culture from representative sputum were used as reference standard to identify pneumococcal aetiology. If S. pneumoniae was detected with at least one of the reference methods the patient was considered having pneumococcal pneumonia. The reference standard was negative if none of these methods turned out positive. In order to identify atypical aetiology, PCR was applied to respiratory tract samples for detection of Mycoplasma pneumoniae and Chlamydophila pneumoniae respectively, and to urinary antigen test for detection of Legionella pneumophila.

Results: The test was positive for S. pneumoniae on NpAs in 86 patients (45%) with pneumonia and in three controls (4.7%). As comparison the test was positive on urine samples in 45 patients (23%) with pneumonia and in one control (1.6%). In 61 patients with pneumonia and positive reference standard the ICT was positive on NpAs in 49 cases. Furthermore, the test was positive in 37 of 132 cases with negative reference standard. Thus, the sensitivity was 80% and the specificity was 72%. If cultures on NpAs were added to the reference standard, the sensitivity was 81% (59/73) and specificity 78% (93/120). Atypical bacteria were detected in 20 patients with pneumonia, of which two patients (10%) were tested ICT positive in NpAs. In this study 98 patients were treated with penicillin G, penicillin V or amoxicillin as monotherapy. Among 41 patients with positive ICT and 57 patients with negative ICT 36 patients (88%) and 38 patients (67%) respectively were cured with no change of antibiotic regime.

Conclusion: The relative high sensitivity in combination with the low number of positive cases among controls and patients with atypical aetiology indicate that ICT applied to NpA could be useful for diagnosing pneumococcal pneumonia. A positive ICT result supports early treatment with penicillin among patients with CAP.