M. pneumoniae and C. pneumoniae are no relevant pathogens in critically ill patients with hospital-acquired respiratory tract infections.

To assess the incidence of Mycoplasma pneumoniae and Chlamydia pneumoniae in the pathogenesis of hospital-acquired respiratory tract infections (RTIs) in critically ill patients. This is a retrospective cohort study of all ICU-patients ≥ 18 years with RTI who underwent conventional culture techniques and PCR testing for both M. pneumoniae and C. pneumoniae from respiratory tract specimens (bronchoalveolar lavage or tracheobronchial aspirates) between January 2013 to May 2017 at the Jena University Hospital. In total, 314 patients were included in the analysis. Of these, 210 (66.9%) patients were diagnosed with HAP, 65 (20.7%) with VAP and 39 (12.4%) with VAT. Overall, 73 (30.7%) patients were on mechanical ventilation on the day of microbiological examination. PCR-testing for M. pneumoniae was positive in two patients (0.6%) and for C. pneumoniae in zero patients. Our study shows that the incidence of M. pneumoniae and C. pneumoniae in the pathogenesis of hospital-acquired RTIs in critically ill patients is negligible. The results support the recommendations of the guidelines not to perform empiric therapy covering these pathogens.