False-Positive Detection of Haemophilus influenzae by a Multiplex PCR Panel in a Neonate With Late-Onset Group B Streptococcal Bacteremia.

Here, we report the case of a term neonate with late-onset Group B Streptococcal (GBS) bacteremia in whom the FilmArray® Meningitis/Encephalitis (ME) panel (BioFire Diagnostics, Salt Lake City, UT, US) falsely detected Haemophilus influenzae in the cerebrospinal fluid (CSF). Although the CSF showed mild pleocytosis and elevated protein, there were no clinical signs of bacterial meningitis. Confirmatory testing, including multiplex PCR targeting H. influenzae (siaT), GBS (cfb), and 16S rRNA, as well as CSF culture, yielded negative results. Repeat FilmArray testing under controlled conditions was also negative. A manufacturer's investigation revealed borderline amplification of only one of the H. influenzae targets, which was interpreted algorithmically as positive. This discordance highlights a key limitation of multiplex PCR panels: the lack of transparency in signal interpretation and threshold settings. The patient demonstrated no immunodeficiency and remained clinically stable during a 10-month follow-up. This case underscores the importance of confirmatory testing when panel results contradict the clinical picture and advocates for improved algorithmic clarity and inter-laboratory validation. Increased awareness of such diagnostic pitfalls is essential, particularly in neonatal settings where unnecessary antimicrobial interventions may pose additional risks.