Estimating the prevalence of coinfection with influenza virus and the atypical bacteria Bordetella pertussis, Chlamydophila pneumoniae, and Mycoplasma pneumoniae.

Coinfections with common bacterial respiratory pathogens and influenza viruses are well-known causes of disease, often via synergistic interactions between the influenza virus, the bacteria, and the human host. However, relatively little is known about interactions between atypical bacteria and influenza viruses. A recent report by Reinton et al. explored this issue by analyzing data from 3,661 patients seeking medical assistance for the presence of Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Bordetella pertussis, as well as influenza A or B virus in nasal swab specimens. The report, however, did not accurately assess the epidemiologic interactions of these pathogens. We aimed to describe the interactions between these bacterial species and influenza infections. Strong and highly statistically significant antagonistic interspecies interactions were detected between C. pneumoniae and influenza virus [odds ratio (OR): 0.09; p < 0.0001) and M. pneumoniae and influenza virus infections (OR: 0.29; p = 0.003). No association was detected between B. pertussis and influenza infection (p = 0.34), contrary to the initial report, and coinfection was not detected at a higher-than-by-chance frequency within the population. Further support of these results is supplied by the analysis of two earlier investigations reporting data on influenza virus and these atypical bacteria. Our results supplement the large body of literature regarding interactions between influenza virus and typical respiratory pathogens, providing a fuller picture of the spectrum of interactions between influenza viruses and respiratory bacteria. Further, we demonstrate the importance of choosing the most appropriate reference populations for the analysis being performed and describe the pitfalls that may occur when care is not taken in this regard.