Pneumococcal C and type polysaccharide detection in the concentrated urine of patients with bacteremia

Evaluation of a rapid immunochromatographic test for detection of Streptococcus pneumoniae antigen in urine samples from adults with community-acquired pneumonia

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia but is undoubtedly underdiagnosed. Isolation of S. pneumoniae from blood is specific but lacks sensitivity, while isolation of S. pneumoniae from sputum may represent colonization. We evaluated a new immunochromatographic test (NOW S. pneumoniae urinary antigen test; Binax, Portland, Maine) that is simple to perform and that can detect S. pneumoniae antigen in urine within 15 min. Urine samples from 420 adults with community-acquired pneumonia and 169 control patients who did not have pneumonia were tested. Urine from 315 (75%) of the pneumonia patients and all controls was tested both before and after 25-fold concentration, while the remaining 105 samples were only tested without concentration. S. pneumoniae urinary antigen tests were positive for 120 (29%) patients with pneumonia and for none of the controls. Of the urine samples tested with and without concentration, 96 were positive, of which 6 were positive only after concentration. S. pneumoniae antigen was detected in the urine from 16 of the 20 (80%) patients with blood cultures positive for S. pneumoniae and from 28 of the 54 (52%) patients with sputum cultures positive for S. pneumoniae. The absence of S. pneumoniae antigen in the urine from controls suggests that the specificity is high. Concentration of urine prior to testing resulted in a small increase in yield. The NOW S. pneumoniae urinary antigen test should be a useful adjunct to culture for determining the etiology of community-acquired pneumonia in adults.

Detection of Streptococcus pneumoniae antigen by a rapid immunochromatographic assay in urine samples

STUDY OBJECTIVES

Evaluation of a newly available rapid (15 min) immunochromatographic membrane test (ICT) to detect Streptococcus pneumoniae in urine samples, in order to assess its utility in the diagnosis of bacteremic and nonbacteremic pneumococcal pneumonia.

DESIGN

Retrospective study.

SETTING

We studied urine samples from 51 patients with bacteremic and nonbacteremic pneumonia due to S pneumoniae diagnosed by blood culture and pneumococcal polysaccharide capsular antigen detection by counterimmunoelectrophoresis in urine samples, 16 patients with probable pneumococcal pneumonia, 71 patients with nonpneumococcal pneumonia, and 16 patients with pneumonia but no pathogen identified. Urine samples were collected and frozen at - 20 degrees C until used. The ICT test was performed following the instructions of the manufacturer.

MEASUREMENTS AND RESULTS

S. pneumoniae antigen was detected in 41 of 51 patients with pneumococcal pneumonia (80.4%); results were positive in 23 of 28 bacteremic cases (82.1%) and in 18 of 23 nonbacteremic cases (78.3%). From patients with a diagnosis of presumptive pneumococcal pneumonia, antigen was detected in seven urine samples (43.7%) and also in one case of the 16 patients with pneumonia but no pathogen identified. The specificity of the ICT test was 97.2%.

CONCLUSION

The ICT assay is a valuable tool for the diagnosis of pneumococcal pneumonia, especially for the nonbacteremic cases.

Detection of C-polysaccharide in serum of patients with Streptococcus pneumoniae bacteraemia

AIM

To investigate the fate of Streptococcus pneumoniae C-polysaccharide antigen in serum in patients with S pneumoniae bacteraemia.

METHOD

In vitro dissociation experiments were performed to demonstrate that C-polysaccharide was masked by ligands in normal and acute phase serum. Serum samples from 22 patients with S pneumoniae bacteraemia were treated to dissociate immune complexes and then tested for C-polysaccharide by enzyme linked immunosorbent assay (ELISA).

RESULTS

C-polysaccharide antigen was masked in normal and acute phase serum but could be released by EDTA treatment and detected by ELISA. Antigen was found in six patients ranging in concentration from 2.5 to 200 ng/ml. Patients with detectable antigen were more likely to die than those in whom antigen was not detected.

CONCLUSION

This study demonstrates that C-polysaccharide antigen commonly circulates in patients with S pneumoniae bacteraemia but its presence is masked by ligands present in serum.

Detection of pneumococcal polysaccharide antigens in the urine of patients with bacteraemic and non-bacteraemic pneumococcal pneumonia

Countercurrent-immunoelectrophoresis (CIE) was used to detect pneumococcal capsular polysaccharide and C-polysaccharide (C-Ps) antigens in urine. The neutral capsular polysaccharides of types 7F and 14 were detected by coagglutination. We found pneumococcal polysaccharide in urine with the same frequency in two groups of patients, i.e. a non-bacteraemic pneumonia group (68%) and a group of patients with pneumococcal bacteraemia (66%). C-Ps was detected in the urine of two patients (4%) and, therefore, this test has no value in the diagnosis of pneumococcal infections. Since there is no sensitive, non-invasive, single procedure for the diagnosis of non-bacteraemic pneumococcal pneumonia we conclude that attempts to detect pneumococcal capsular polysaccharide by CIE in combination with coagglutination (types 7F and 14) may be a useful diagnostic supplement in the search for the etiological agent in pneumonia in adults until new, more sensitive diagnostic methods have been developed.

Antigen detection in pneumococcal pneumonia

Streptococcus pneumoniae remains the commonest proven cause of community-acquired pneumonia in patients admitted to hospital, but no currently available diagnostic method can be regarded as a gold standard. Microscopy of sputum is usually considered insensitive and poorly specific, and more invasively-obtained specimens are not routinely collected. Cultures of blood and respiratory secretions, and countercurrent immunoelectrophoresis (CIE) and particle agglutination-based assays for capsular polysaccharides in serum and urine specimens, are specific but less than ideally sensitive. Some workers have reported specificity problems when immunoassays are applied to respiratory secretions. New diagnostic methods include detection of pneumococcal C polysaccharide in sputum and urine by ELISA and particle-agglutination assays, and these appear promisingly sensitive and specific in preliminary studies. Clinical assessments are now required to define the role of these techniques in guiding the treatment of individual patients.