Haemophilus influenzae and SARS-CoV-2: Is there a role for investigation?

During the current pandemic of COVID-19, the authors observed that during screening test for SARS-CoV-2 targeting the E-gene by qRT-PCR, few nasopharyngeal/oropharyngeal samples showed amplification signals at late cycle threshold (C(T)-value) > 35 despite being negative for other confirmatory target genes. Thirty such samples (taken as cases) showing detectable C(T) of > 35 cycle in E-gene which were negative for other target genes of SARS-CoV-2 and 30 samples with undetectable fluorescence in E-gene were taken as controls for investigation. An in-vitro diagnostic approved commercial qRT-PCR multiplex kit detecting 33 respiratory pathogens which can also detect Haemophilus influenzae was used for screening the samples. It was observed that out of the 30 samples showing detectable C(T)> 35 in E-gene, 11 samples were positive for Haemophilus influenzae whereas in the controls only three samples were positive for H. influenzae (p-value: 0.03) which was statistically significant. Further, the probes and primers were screened against H. influenzae for matches in the genome. It was observed that all primers and probes for the E-gene of SARS-CoV-2 had over 13 bp long sequences matching 100% with multiple sites across the H. influenzae genome. This qRT-PCR primer & probes are being used extensively across India, and laboratories using them should be aware of the cross-reactivity of primers & probes with the H. influenzae genome. Further, the authors observed that 95.9% (5415/5642) of COVID-19 positive cases detected in their laboratory were asymptomatic at the time of collection of samples. This warrants further investigations.