Novel urinary antigen test boosts S. pneumoniae CAP detection

Research published in the European Respiratory Journal shows that addition of a serotype-specific urinary antigen detection test to existing diagnostic methods can increase the detection of Streptococcus pneumoniae community-acquired pneumonia (CAP) by over a third.

“Although not commercially available, this approach could enhance our diagnostic yield for pneumococcal infections and could provide more detailed information on the epidemiology of infection-associated pneumococcal serotypes,” say authors Susanne Huijts (University Medical Center Utrecht, the Netherlands) and colleagues.

The study involved 23 Dutch hospitals, and 1095 adult patients with radiographically confirmed CAP.

Standard microbiologic culture results and immunochromatographic assay urinary antigen testing identified the etiologic cause in 36.8% of episodes and S. pneumoniae was deemed the probable or definite pathogen for 23.5% of episodes.

By contrast, with the addition of serotype-specific urinary antigen detection test results, these figures rose to 45.0% and 32.6%, respectively, equating to a 39% relative increase in the diagnostic yield for S. pneumoniae.

The novel test, which is a multiplex assay for 13 pneumococcal serotypes, had improved diagnostic accuracy over the standard urinary antigen test with 48 out of 49 bacteremic isolates belonging to these serotypes giving a positive result. This equated to a 98% sensitivity compared with 69% for the latter test, which only yielded a positive result for 34 of these 49 episodes. The specificity of the two tests was the same at 100%.

Huijts et al say the results show that the serotype-specific test could enhance investigations of the serotype-epidemiology of S.pneumoniae.

“Moreover, if the turnaround time of this test could be reduced to that of a real-time test, demonstrating S.pneumoniae as a cause of CAP could assist in rapid de-escalation of unnecessarily broad antibiotic treatment for CAP,” they add.

The researchers note that the new test also revealed that 4.4% of cases appeared to be caused by multiple serotypes, a phenomenon that has been sporadically reported in the past.

“Thus, apart from higher sensitivity, the [urinary antigen detection] test also improves our capacity to detect co-infections with multiple serotypes,” they conclude.

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