1040. Use of the BinaxNOW Streptococcus pneumoniae Urinary Antigen Test in a Diagnostic Algorithm to Detect Invasive Pneumococcal Disease
Session: Poster Abstract Session: Diagnostic Procedures in Clinical Practice
Saturday, October 22, 2011
Room: Poster Hall B1
Background: Invasive pneumococcal disease (IPD) is a serious clinical condition. Timely diagnosis can be critical and influence antibiotic therapy. In adults, up to 87% of pneumococcal bacteremia is associated with pneumonia. High levels of C-reactive protein (CRP) in patients with community-acquired pneumonia are suggestive for a pneumococcal etiology. Although specificity is excellent, sensitivity of S. pneumoniae recovery from blood and respiratory specimens is low. We combined the level of CRP and new infiltrates on chest radiography with a urinary antigen test in an algorithm to optimize the diagnosis of IPD.

Methods: Between March 2008 and March 2011, a  S. pneumoniae urinary antigen test (BinaxNOW) was performed on unconcentrated urine samples from patients with a clinical suspicion of IPD. Urine of patients with proven IPD or hemocultures positive for other streptococci were tested to demonstrate sensitivity and specificity. From November 1, 2009 onwards, clinicians could order the test upon clinical suspicion of pneumonia, regardless of  CRP-levels. Tests were performed 24/24h in STAT modus and communication about results was standardized.

Results: The antigen test was performed on 466 urine samples from 459 patients. Data were assigned to 4 different groups. Group 1 contained patients with proven IPD. A sensitivity of 62.5% (40/64) was observed. All patients with blood cultures (BC) positive for streptococci (n=21) were enrolled in group 2. As one patient with a S. mitis bacteremia had a false positive result, specificity was 95.2% (20/21).  The positive predictive value (PPV) was 97.1%.Patients with clinical suspicion of IPD and negative or missing BC, were divided in those with CRP-values ≥ 200 mg/L (group 3; n=238) and those with levels < 200 mg/L (group 4; n=143). We observed a higher percentage of positive antigen tests when CRP ≥ 200 mg/L (22.7% vs. 8.4%; p<0.05).

Conclusion: The BinaxNOW S. pneumoniae urinary antigen test can supplement the microbiological diagnosis of IPD, especially in patients with negative or missing blood cultures.
Specificity and PPV of the test are high and allow clinicians to optimize antimicrobial treatment.
22.7% of patients with CRP ≥ 200 mg/L, chest infiltrate and missing or negative BC have a positive antigen test. 

Subject Category: J. Clinical practice issues

Charlotte Verfaillie, PharmD1, Stefanie Drieghe, PharmD1, Jos Van Acker, MD1, Dirk Ommeslag, MD2 and Anne-Marie Van den Abeele, MD1, (1)Medical microbiology, Sint-Lucas Hospital, Ghent, Belgium, (2)Internal Medicine, Sint-Lucas Hospital, Ghent, Belgium


C. Verfaillie, None

S. Drieghe, None

J. Van Acker, None

D. Ommeslag, None

A. M. Van den Abeele, None

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