Few CAP Patients Get Urinary Antigen Testing

Only about 15% of patients hospitalized with community-acquired pneumonia had pneumococcal urinary antigen testing performed, an assay that can help narrow or de-escalate their course of therapy, researchers found.

More than half of patients received empiric treatment, but less than 20% had antipseudomonal or anti-methicillin resistant Staphylococcus aureus (MRSA) treatment de-escalated within 3 days, in spite of negative bacterial cultures, reported Michael Rothberg, MD, of the Cleveland Clinic in Ohio, and colleagues.

Patients who had a positive urinary antigen test were more likely to have empiric therapy narrowed by day 3, though rates of de-escalation varied by hospital, they wrote in Clinical Infectious Diseases.

Rothberg’s group noted that the Infectious Diseases Society of America (IDSA) and American Thoracic Society consensus guidelines recommend diagnostic testing for the etiology of community-acquired pneumonia “when knowledge of the specific pathogen would alter management decisions.” Thus, urinary antigen testing would be recommended when broad-spectrum empirical antibiotics are recommended, including cases of severe community-acquired pneumonia, failure of outpatient antibiotics, severe chronic liver disease, or pleural effusion, they wrote, and in those cases, positive tests for Streptococcus pneumoniae should “allow for rapid de-escalation of antibiotic therapy.”

But urinary antigen testing is rarely recommended outside of the intensive care unit (ICU), the authors said, and not for all patients on broad-spectrum antibiotics.

“Since the guidelines stipulate that non-ICU patients should receive empiric therapy with agents that offer appropriate coverage for S. pneumo, there would presumably be no role for [urinary antigen testing] outside the ICU. Despite the guidelines, however, a growing percentage of [community-acquired pneumonia] patients are treated with empiric agents having activity against MRSA and resistant gram negative organisms,” they wrote.

“In these cases, [urinary antigen testing] would be guideline-concordant and represents an opportunity for antibiotic stewardship,” the authors added.

Researchers examined data from the Premier database from 2010 to 2015 on almost 160,000 adult patients treated at 170 U.S. hospitals for community-acquired or healthcare-associated pneumonia.

Among larger hospitals with at least 100 patients, use of urinary antigen testing varied widely — from 0% to 69%. Patients who had urinary antigen testing were younger, less likely to have aspiration pneumonia, and more likely to have sepsis, and be admitted to the ICU.

Not surprisingly, patients with a positive urinary antigen test were significantly more likely to have a positive S. pneumoniae culture compared to those with a negative urinary antigen test (25.4% vs 1.9%, respectively; P<0.001) and had resistant bacteria significantly less often (5.2% vs 6.8%; P<0.05).

The authors also found that around 61,000 patients received an antipseudomonal drug other than a fluoroquinolone or an anti-MRSA drug empirically, and only 16% of those underwent urinary antigen testing. Median duration of broad-spectrum antibiotics for patients with a positive urinary antigen test was 3 days, compared with 4 days for a negative test and 5 days for those with no test. Duration of vancomycin, piperacillin-tazobactam, and carbapenems were all shorter following a positive urinary antigen test, the authors said, and the rate of de-escalation following a positive test “tended to increase with increasing hospital use.”

Among the 1,582 patients who underwent urinary antigen testing and were de-escalated by day 3, 4.4% died, which was similar among those with a positive or negative test, they noted. There were 3% of patients who were transferred to the ICU on day 3 or later. They added that only one patient with a positive urinary antigen test was subsequently admitted to the ICU.

So Why Not Use This Test More?

An accompanying editorial by Sameer Kadri, MD, of the NIH Clinical Center in Bethesda, Maryland, praised the study, saying “the design is clever, analysis is robust and inferences seem fairly within the context of the limitations besetting epidemiologic studies that leverage large real-world databases.”

“[Pneumococcal urinary antigen testing] is simple, has a rapid turnaround, outperforms respiratory cultures, is unaffected by pre-treatment with antibiotics and is affordable relative to many other tests that we order nowadays,” he wrote.

But Kadri also listed barriers to use of this test, mainly non-availability. Or when the test was available, it was a “send-out,” which diminished its usefulness. He added that hospitals may not adopt this type of testing in-house due to logistical reasons.

Kadri offered some thoughts on the best population to use urinary antigen testing — ranging from all community-acquired pneumonia patients to severe patients, as suggested by the guidelines, or a smaller population, such as patients with community-acquired pneumonia “where sputum is not obtainable for gram-stain or where cultures are negative at 48 hours.”

Regardless, he wrote that “frequent scrutiny of real-world care patterns may fill important gaps in our knowledge, especially in between infrequently updated labor-intensive practice guidelines.”

“We are naive to assume that guidelines are being consistently followed,” Kadri added.

Limitations to the study by Rothberg and colleagues include the potential for unmeasured confounding, the exclusion of patients treated with quinolone monotherapy, and that the study was conducted from 2010 to 2015, “when not all hospitals had easy access to [urinary antigen testing].”