Case Report: Coinfection of influenza A and Chlamydia psittaci pneumonia.

The coinfection of influenza A and Chlamydia psittaci pneumoniae is rarely described in China. However, the clinical features of these diseases pose a significant diagnostic challenge. Therefore, it is necessary to report and review such a potentially fatal case. We report an 89-year-old male patient requiring admission to the intensive care unit with acute hypoxemic respiratory failure, shock and MODS. He presented with fever, fatigue, anorexia and dyspnea. The patient exhibited severe hypoxemia, shock, hepatic dysfunction (elevated liver enzymes and serum bilirubin), acute kidney injury and a SOFA score of 17. Mechanical ventilation (MV) and venous-venous extracorporeal membrane oxygenation (VV-ECMO) were established for respiratory support. The initial diagnosis focused on influenza A for his positive influenza A nucleic acid. However, the patient's imaging presentation was not coupled with viral pneumonia, which raised suspicion for other pathogens. Metagenomic next-generation sequencing (mNGS) detected coinfection of C psittaci, influenza A H3N2 virus, and Klebsiella pneumoniae in bronchoalveolar lavage fluid. Concurrent targeted NGS (tNGS) detected C. psittaci in blood. Omadacycline and baloxavir marboxil were prescribed. The patient's condition improved, and he was successfully weaned from VV-ECMO and MV. He was discharged and recovered on day 60 of the follow-up. This case underscores the diagnostic complexity of coinfection and the use of NGS testing in this severe condition and the role of omadacycline in psittacosis.