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 <i>Haemophilus influenzae</i> 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 <i>H. influenzae</i> (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 <i>H. influenzae</i> 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.