Meningitis Test Could Reduce Unnecessary Admissions

Test Can Remain Positive After Antibiotic Pretreatment

Table1: BioFire Film Array
Meningitis/Encephalitis Panel

Whether you get anxious while awaiting head CT results and slip in a dose of ceftriaxone or have a patient who has taken oral antibiotics, bacterial DNA can still be detected in many (not all) cases by the BioFire assay, even though some bacteria may not grow on traditional media.³ Although antibiotic susceptibilities are not currently available, rapid bacterial identification, sometimes even in the face of prior antibiotics, allows more targeted treatment and, in the case of meningococcal infection, public health notification and close-contact prophylaxis or, alternatively, reassurance to the staff.

The BioFire assay has limitations. First, it does not test for some common causes of encephalitis, like West Nile or the emerging Eastern equine encephalitis virus. As with other polymerase chain reaction assays, the test may be negative in early herpes simplex virus encephalitis. Second, while false negatives are rare for typical bacteria in non-pretreated patients, false positives occasionally occur, such as with pneumococcus, which is thought to be due to specimen contamination during specimen handling (your sterile technique counts). As with any test, the result should be correlated with all available epidemiological, clinical, and lab data. Third, caution should be exercised in patients with subacute symptoms since, for example, tuberculosis and fungi other than Cryptococcus are not included in the panel. Caution should also be exercised in immunocompromised patients, for whom the risk of misdiagnosis is higher and a greater range of pathogens must be considered. For example, the current standard cryptococcal antigen test appears to be more sensitive for this pathogen than the BioFire test. Fourth, the assay does not test for staphylococcal species and gram-negative pathogens that are sometimes seen in neurosurgery-related infections. Finally, the test is an additional expense—the manufacturer’s charge is $130 per cartridge after purchase of the FilmArray system (which can also run stat respiratory, pneumonia, gastrointestinal, and blood panels) for about $50,000. It is best targeted for stat use after standard CSF test results are back and diagnostic uncertainly remains.

Acknowledgement: Dr. Talan thanks his residents, Dr. Randy Lee and Dr. Cameron Harrison, for their review and suggestions on this article.

Dr. Talan is professor of emergency medicine/medicine-infectious diseases at the David Geffen School of Medicine at UCLA in Los Angeles and the University of Iowa in Iowa City.