The Binax NOW Streptococcus pneumoniae test applied on nasopharyngeal aspirates to support pneumococcal aetiology in community-acquired pneumonia

Abstract

The use of nasopharyngeal secretions to enhance diagnostic yields of pneumococcal aetiology in community-acquired pneumonia (CAP) is of interest. We evaluated the Binax NOW Streptococcus pneumoniae immunochromatographic test (ICT) on nasopharyngeal aspirates (NPA) in order to support pneumococcal aetiology in CAP. The NPA ICT was applied on 180 adult CAP patients and 64 healthy controls. The rate of pneumococcal detection in the nasopharynx was compared to rates for lytA polymerase chain reaction (PCR) and culture on NPA. According to blood and sputum culture and urine ICT, the test sensitivity in 59 patients with a pneumococcal aetiology was 81%. The specificity was suboptimal, with 72% negative tests among CAP patients without a pneumococcal aetiology. However, the test was positive in only 11% of patients with atypical pneumonia and in 4.7% of healthy controls. The positivity rate was higher for NPA ICT compared to culture on NPA in all CAP patients, and to both PCR and culture on NPA in non-pneumococcal non-atypical CAP patients. In 113 (63%) patients with β-lactam monotherapy, cure without treatment alteration was noted more often in cases with positive compared to negative NPA ICT at admission (91% vs 69%; p < 0.01). The high sensitivity and the low positivity rates in patients with atypical pneumonia and healthy controls, in combination with the correlation between positive test results and clinical cure with β-lactam therapy, may support a pneumococcal aetiology in CAP in populations with low pneumococcal carriage rates.