U.S. hospitals infrequently use pneumococcal urinary antigen tests (UAT) to identify Streptococcus pneumoniae infection and subsequently de-escalate antibiotics. Researchers whose findings appear in Clinical Infectious Diseases said this has implications for improving antimicrobial stewardship.

The Infectious Diseases Society of America/American Thoracic Society (IDSA/ATS) recommend UAT whenever broad-spectrum empiric antibiotics are recommended. The test can identify pneumonia in patients with S. pneumoniae, thus allowing for rapid de-escalation of antibiotics. IDSA/ATS mainly reserve UATs for patients in intensive care (ICU), though they do recommend this testing if a result could potentially change antibiotic management. “Despite the guidelines, however, a growing percentage of patients with CAP [community acquired pneumonia] are treated with empiric agents having activity against methicillin-resistant Staphylococcus aureus and resistant gram-negative organisms. In these cases, UAT would be guideline-concordant and represents an opportunity for antibiotic stewardship,” noted the investigators.

UAT has several advantages including being more sensitive than cultures, easy to perform, inexpensive, and rendering quick results. Performance varies among UATs, however, and not many studies have looked at its uses in clinical practice. To examine how often physicians order UATs and if the results impact antibiotic de-escalation, the investigators conducted a retrospective study of adult patients with CAP or healthcare-associated pneumonia admitted to 170 U.S. hospitals.

They initially used a large database of hospitalized patients with pneumonia to correlate results of S. pneumoniae UAT with cultures of sputum and blood, Jennifer Schimmel, MD, co-director of the Antimicrobial Stewardship Program at Baystate Health in Springfield, Massachusetts, and the study’s lead author, told CLN Stat. “However, we also had information about antibiotic use, so this research evolved to also examine the ‘real world’ use of UAT as an antibiotic stewardship tool.”

Among nearly 160,000 admissions, just 24,757 involved a UAT (18.4% of ICU and 15.3% of non-ICU patients). The rate of testing ranged widely among the hospitals, from 0% to 69% among those with ≥100 eligible patients. About 1 in 3 hospitals conducted no UATs at all, and in another third, less than 10% of all patients received UATs. “However, overall utilization of UAT rose steadily and doubled during the 5-year study period,” noted the investigators.

Patients who received the test were generally younger, more likely to have sepsis, and less likely to have aspiration pneumonia. Those initially admitted to the ICU were also more likely to have UAT. “We included this finding because the guidelines only recommend UAT for patients in the ICU. After a UAT was ordered, patients with UAT were less likely to be transferred to ICU (although not statistically significantly so),” Michael Rothberg, MD, director of the Cleveland Clinic’s Center for Value-Based Care Research and the study’s senior author, told CLN Stat.

Those with positive results had higher rates of S. pneumoniae isolated from blood or sputum than those with negative results but were less likely to grow other organisms. Overall, positive results correlated with fewer resistant organisms, but this usually didn’t lead to antibiotic de-escalation.

Although patients with a positive UAT were more likely than those with a negative result to have their antibiotics de-escalated, de-escalation occurred in just one-third of patients with a positive UAT. “We were not able to make definitive conclusions about the safety of antibiotic de-escalation for patients with a positive UAT, but hospitals with high rates of UAT did not have worse outcomes, and patients whose antibiotics were de-escalated after UAT were very unlikely to undergo re-escalation,” said Schimmel.

UAT appears to be a useful tool for identifying patients at high risk for S. pneumoniae and subsequently de-escalating broad-spectrum empiric antibiotics. “As the IDSA formulates its next set of CAP/HCAP guidelines, consideration should be given to broadening the population of patients who could benefit from UAT and offering more specific guidance regarding the appropriate response to positive UAT,” the investigators recommended.

Clinical labs can work with their local stewardship committees to consider making UAT a routine test—at least when broad-spectrum empiric antibiotics are being considered, Rothberg suggested. “For patients getting routine CAP therapy (a cephalosporin plus a macrolide, for example), then there is less need to make this diagnosis, because almost all S. pneumoniae will be sensitive to this treatment,” said Rothberg.

Why clinicians don’t use UAT more often is unclear. Perhaps it’s because IDSA/ATS guidelines recommend using UAT just for ICU patients instead of for all patients receiving broad-spectrum antibiotics. Yet, testing rates between ICU and non-ICU patients in the study differed by only a few percentages, “suggesting that guidelines had minimal effect on physician ordering,” the investigators reported. Doctors might not also feel confident with the specificity of UAT.

Sameer S. Kadri, MD, in a related editorial praised the study’s ingenuity. “The design is clever, the analysis is robust, and the inferences seem fairly within the context of the limitations besetting epidemiologic studies that leverage large, real-world databases,” he wrote. But the research only reflects in-house testing of hospitals, which suggests it underestimates real-world use of UAT, he continued.

Kadri also suggested that logistical reasons might explain why more hospitals aren’t investing in UAT: Labs might be seeing low case volumes, or clinician demand for the test isn’t that robust. The UAT or pneumococcal urine antigen test (PUAT) also has a short, 2-year shelf life, he added.

He also questioned how big of an impact a UAT-guided stewardship approach could have on public health. “Analyses from Germany, the United Kingdom, and Canada warn us that routine use of PUAT may, in fact, not be cost-effective for narrowing therapy; similar, robust assessments within the U.S. healthcare system are necessary, as cost-effectiveness will likely dictate whether PUAT becomes a mainstream implement for stewardship in the future.”