Severe pneumonia due to concurrent Legionella pneumophila and Acinetobacter baumannii infections: a case report

Abstract

Background: Legionella pneumophila is an uncommon pathogen causing community-acquired atypical pneumonia. Acinetobacter baumannii is a major pathogen responsible for hospital-acquired pneumonia, but it rarely causes serious infections in a community setting. Without prompt and appropriate treatments, infection from either of these two pathogens can cause a high mortality rate. Concurrent infection from both L. pneumophila and A. baumannii can cause serious outcomes, but it has rarely been reported previously.

Case presentation: A 45-year-old male presented to our hospital with a productive cough and fever after staying in a local hotel. His chest computed tomography (CT) scan showed bilateral lower-lobe infiltration and left pleural effusion. Empirical antibiotics, including piperacillin-tazobactam, levofloxacin, meropenem, and doxycycline, were administered to him to treat community-acquired pneumonia. However, his condition deteriorated very rapidly, and he required endotracheal intubation and mechanical ventilation for respiratory support. Finally, metagenomic next-generation sequencing (mNGS) of his bronchoalveolar lavage fluid identified L. pneumophila and A. baumannii. The sputum culture demonstrated multidrug-resistant A. baumannii. He was diagnosed with pneumonia by concurrent infections from both L. pneumophila and A. baumannii. After careful consideration of the antibiotic susceptibility results and the antibacterial mechanism of each antibiotic, we switched the antibiotics to omadacycline and cefoperazone/sulbactam. His clinical symptoms gradually subsided. The repeat chest CT image showed no infiltration or pleural effusion.

Conclusions: Community-acquired pneumonia can be caused by concurrent infections of both L. pneumophila and A. baumannii. Close clinical monitoring, early pathogen detection and antibiotic susceptability tests, and appropriate antibiotic regimen adjustments should be applied to these patients who failed initial antibiotic treatments.

Keywords: Acinetobacter baumannii; Legionella pneumophila; Case report; Metagenomic next-generation sequencing; Pneumonia.

Fig. 1

Clinical timeline. BAL, bronchoalveolar lavage; CT, computed tomography; ICU, intensive care unit; MDR, multidrug resistance; mNGS, metagenomic next-generation sequencing; P/F, partial pressure of oxygen in arterial blood/fraction of inspiratory oxygen concentration

Fig. 2

Chest computed tomography (CT) scans. A, CT at hospital presentation (July 3, 2022), showing bilateral lower-lobe infiltration with left pleural effusion. B, CT scan at two days after hospital admission (July 5, 2022), showing increased bilateral lower-lobe infiltration. C, CT scan at four days after treatment for L. pneumophila and A. baumannii infection (July 12, 2022), showing significantly decreased bilateral lower-lobe infiltration. D, CT scan at nine days after treatment (July 17, 2022), showing almost completely resolved bilateral lower-lobe infiltration. E, CT scan at the clinical follow-up visit on April 15, 2024, showing no infiltration

Fig. 3

The metagenomic next-generation sequencing of the bronchoalveolar lavage fluid showing positive results for L. pneumophila and A. baumannii. The sequence read refers to the number of specific sequences that can be uniquely matched to a certain bacterial genus or species. The relative abundance refers to the proportion of a certain microbial genus or species in the microorganisms detected in the entire specimen. A high abundance corresponds to a great proportion of certain bacteria. The Q index refers to the content of different microbial nucleic acids in the specimen, which is calculated through the measured value of the internal standard molecule. A high Q index corresponds to a high microbial content and a high accuracy in pathogen detection