Pneumococcal Urinary Antigen Testing Guides Antimicrobial Treatment

September 30, 2010 — A positive pneumococcal urinary antigen test result in adult patients hospitalized with community-acquired pneumonia (CAP) can help clinicians optimize antimicrobial therapy and achieve good clinical outcomes, according to a new study published Online First September 27 in the Archives of Internal Medicine.

"A quick and simple urinary antigen test, based on an immunochromatographic membrane technique, is widely available to detect the C-polysaccharide antigen of Streptococcus pneumoniae, the leading cause of CAP," write Roger Sordé, MD, from Hospital Universitari Vall d'Hebron, Barcelona, Spain, and colleagues. "This test has demonstrated reasonable sensitivity and good specificity in different studies. Nevertheless, the clinical usefulness of this pneumococcal urinary antigen test is not well defined, and, consequently, current guidelines do not clearly recommend the situations in which testing should be performed."

The aim of this study was to assess the usefulness of pneumococcal urinary antigen detection in the diagnosis and antimicrobial guidance in patients hospitalized with CAP.

The investigators prospectively studied all consecutive adult patients 16 years and older who were hospitalized with CAP from February 2007 through January 2008.

A total of 474 episodes of CAP in 464 patients were included. Most (66.9%) of the patients were men, 33.1% were women, and mean age was 64 years.

S pneumoniae was identified as the causative pathogen in 171 (36.1%) of the cases. It was detected exclusively by urinary antigen testing in 75 cases (43.8%). In 69 patients, CAP was caused by a pathogen other than S pneumoniae.

The study authors report that the specificity of the pneumococcal urinary antigen test was 96% and that its positive predictive value ranged from 88.8% to 96.5%. The positive likelihood ratio ranged from 14.6 to 19.9.

Positive results from the test led clinicians to reduce the spectrum of antibiotic treatment in 41 patients (8.6%). These reductions included improved modification of empiric therapy in 18 cases and optimal modification of empiric therapy in 23 cases.

The median time to implement these modifications was 1 day (interquartile range [IQR], 1 day) in the improved adjustments group, and 3 days (IQR, 3 days) in the optimal group. Globally, the median time to a treatment optimization from the pneumococcal urinary antigen test result was 2 days (IQR, 2.5 days), the study authors report.

Pneumonia was cured in all of the patients.

"In our study, patients started the targeted therapy during the first to third day after admission, and the good clinical outcomes assessed in the 41 patients who received a favourable adjusted therapy suggest that a targeted therapy for pneumococcus is a valid strategy to treat inpatients with CAP," the study authors write. "We also did not observe any relapse in the 23 patients with an optimal adjustment."

Pointing out their study limitations, the study authors note that they did not study the duration of test positivity after pneumococcal infection and also that specific diagnostic tests were performed according to the attending physician, which prevented them from including complete microbiological data for all patients. That the study was nonrandomized is another potential limitation.

"In conclusion, because of its high specificity, positive predictive value, and positive LR [likelihood ratio], we think that the urinary detection of pneumococcal antigen is a useful tool in the treatment of adult patients with CAP," the study authors write. "When findings are positive, it allows clinicians to optimize antimicrobial therapy with good clinical outcomes."

They add: "In our opinion, this test should be incorporated into clinical guidelines at the same level as classic microbiological studies because it can supplement, but not replace, their results."

This study was institutionally supported by the Spanish Network for Research in Infectious Diseases (REIPI), RD06/008, from the Ministry of Science and Innovation, "Instituto de Salud Carlos III."

The study authors have disclosed no relevant financial relationships.

Arch Intern Med. Published online September 27, 2010.