Respiratory tract infections during the 2011 Mycoplasma pneumoniae epidemic

In 2011, Norway experienced a surge in community acquired Mycoplasma pneumoniae infections. Norway also has one of the highest rates of reported Bordetella pertussis infections, despite high vaccine coverage. We aimed to determine the prevalence of upper respiratory tract pathogens in patients attending primary care physicians for respiratory illness during the 2011 M. pneumoniae epidemic period. A retrospective analysis of data from 26,039 patients that have had nasopharyngeal swabs analysed by nucleic acid amplification testing (NAAT) for M. pneumoniae, C. pneumoniae and B. pertussis was performed. Subsets of samples were tested for additional pathogenic bacteria, including B. parapertussis and B. holmesii, as well as influenza virus. M. pneumoniae, C. pneumoniae and B. pertussis were detected in 2,484 (9.5 %), 261 (1.0 %) and 821 (3.2 %) patients, respectively. Co-infection of M. pneumoniae and B. pertussis was found in 50 (0.19 %) patients, C. pneumoniae and B. pertussis in 4 (0.02 %). Influenza virus was found in 899 (24.5 %) of 3,661 nasopharyngeal swabs. Co-infection of influenza virus and bacterial pathogens was common, although influenza virus co-infection with B. pertussis occurred significantly more often than with C. pneumoniae and M. pneumoniae (20.4 % versus 2.9 % and 9.1 %, respectively; p<0.005). Testing for Bordetella species genes IS1001, IS1002 and recA showed that B. holmesii was most likely misdiagnosed as B. pertussis in 5.8 % of cases. The most prevalent respiratory tract pathogen in the general population in 2011 was M. pneumoniae. B. pertussis was also found frequently as was B. pertussis and influenza virus co-infections.