Healthcare-Associated Pneumonia Pathogens Testing Has Limited Success

Testing for pathogens in patients with healthcare-associated pneumonia (HCAP) provides results in less than one-third of cases, according to recent preliminary findings.

In a six-year retrospective study, a pathogen was isolated from 31% of samples taken from nearly 1,600 patients with HCAP, according to Karl Madaras-Kelly, M.D., from the Veterans Administration (VA) Medical Center (Boise, ID, USA).

The finding is important because guidelines for treatment in such cases suggest broad antibiotic therapy with several drugs, followed by modification once a pathogen is identified, Dr. Madaras-Kelly reported her findings at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), held September 2009 in San Francisco, CA, USA. "If you can't identify a pathogen," Dr. Madaras-Kelly said, "you can't really stop [unsuitable] drugs."

The study period--from 2003 through 2008--covers the period before and after the 2005 guidelines were issued by the Infectious Diseases Society of America. The investigators examined records of all patients admitted for pneumonia at six VA medical centers in the northwestern United States, finding 1,568 who met criteria for healthcare-associated pneumonia. Of those, according to Dr. Madaras-Kelly, 92.6% provided one or more cultures, including 81.8% of the total from blood, 49.7% from sputum, and 1.5% from bronchoscopy. However, out of those 1,452 patients with a culture, only 486 (31%) had a pathogen isolated, he noted.

There was no significant year-by-year difference in the proportions with an isolated pathogen, according to Dr. Madaras-Kelly. However, some of the six study sites did better in collecting quality cultures--with result ranges from 6.3-43.6%. The differences were significant at p < 0.001. Dr. Madaras-Kelly noted that clinicians "do adjust treatment when they have a quality culture, but the majority of patients don't have a good culture."

The implications, according to Dr. Madaras-Kelly, include a need to focus on retrieving good quality cultures. "And we also need better methods to diagnose pneumonia because cultures are expensive," he added.

The study's findings have to be interpreted in light of other research suggesting that a pathogen is isolated only 40% of the time in community-acquired pneumonia, according to Lindsay Grayson, M.D., from Austin Hospital (Melbourne, Australia). Dr. Grayson, one of the ICAAC meeting's program cochairs, was not part of the research.

One reason for the failure rate is that patients are frequently given antibiotics before the testing. "[It's] not enough to cure them but enough to confuse the cultures," Dr. Grayson said, and a similar issue may arise with healthcare-associated pneumonia. He stated that the study calls into question "the timing of cultures in relation to any recent antibiotics" and stressed the value of accurate samples.

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