Mythbusting

Molecular CAP testing is coming…

Two institutes in the UK collected sputum or endotracheal aspirate for multiplex real-time PCR assay in 323 patients with radiologically confirmed and admitted community acquired pneumonia patients. Essentially, a test looking for 26 bacterial and 8 viral pathogens. They go a step further and calculate bacterial loads for 8 pathogens they screened for. Notably, cystic fibrosis and HCAP patients were excluded. (49.4% of patients were CURB score of 0 or 1, while 25.4% of patients were PSI class 1 or 2 indicating that these patients could have gone home).

On the surface, seeing a pathogen detected 87% of the time vs 39% of the time for culture based methods seems like a win. Even after receiving antibiotics within 72 hours, 78% of the time a bacterial pathogen was detected vs 32% of the time in culture.

Of course, the authors set us up for more expensive testing: “It is difficult to interpret PCR results for typical respiratory bacteria in nonsterile samples such as sputum due to the potential for contamination with the same organisms from oropharyngeal flora. However, accurate molecular quantification of bacterial loads may aid in distinguishing infection from contamination in a way that is analogous to the use of quantitative cultures.”

But should be fall for this? Neither culture nor PCR positivity was associated with mortality. Polymicrobial infections were not associated with outcome. And while bacterial load of S pneumonia was associated with a higher 30 day mortality – so were higher PSI and CURB-65 scores…. and when you correct for CURB-65 scores, bacterial load was no longer associated with outcomes.

In an age where various medical entities have a history of expanded use resulting in increased costs with little to no net gains (“elective” cardiac caths, MRI for TIAs, outpatient PICC lines for infectious processes that there is an oral equivalent for, etc), I have a hard time believing this will impact the population to whom it will be pitched. There may be a chance to de-escalate antibiotic regimens, but antibiotics are a very small piece of the resuscitation puzzle. Focusing on early pressors, decreasing ED boarding, and aggressive source control in conjunction with an EGLS resuscitation will improve outcomes. Might we save a few ICU days or inpatient days? Perhaps. But we know we can do it with the above mentioned improvements for sepsis care which we are more often than not failing to do. Ultimately, this is looking for an easy fix that is already in front of us and we are opting not to do.

Now lets talk about the amount of money spent on this testing for which it will not be indicated: the outpatient treated patient. The COPD patient with a flare. The radiographically negative URI. FUO patients. Patients in whom many of us will still give zithromax because of sensitivity only at 87%…

Standard

One thought on “Molecular CAP testing is coming…

  1. Pingback: No Magic for MagicPlex PCR. | EM in Focus

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