Legionella, a bacterial genus that is widespread in aquatic environments, enters human alveolar macrophages via the respiratory tract and causes Legionnaires’ disease (Mondino et al., 2020). Legionella bozemanae, which was first isolated in 1959 from the lung tissue of a navy diver, is a rare cause of Legionnaires’ disease, accounting for 3%–5% cases of pneumonia caused by Legionella (Bozeman et al., 1968; Mitchell et al., 1984; Reingold et al., 1984). The associated mortality rate is up to 40% (Taylor and Albrecht, 1995). Diagnosis is difficult because this species is insensitive to serological tests and urinary antigen tests for L. pneumophila serogroup 1 (Guyard and Low, 2011; Widmer et al., 2007). Here we report a case involving an immunocompromised patient in China who developed Legionnaires’ disease caused by L. bozemanae. The clinical manifestations included cough, expectoration, lung infiltration, fever, and dyspnea. Second-generation sequencing of plasma and bronchoalveolar lavage fluid (BALF) showed positivity for L. bozemanae. After anti-infective treatment with rifampicin, moxifloxacin, azithromycin, piperacillin/tazobactam, the patient gradually recovered. To our knowledge, this is the first time that L. bozemanae has been isolated from patient sample in China, and the findings are expected to provide a reference for clinical diagnosis.

The patient was a 50-year-old male farmer with a 30-year history of smoking 5–20 cigarettes per day and social drinking. On August 24, 2022, he was admitted to a hospital in Beijing with fever, cough, yellow sputum, and progressively worsening dyspnea for 9 days. Eight days before admission, he developed a fever after taking a bath and turning on the air conditioner. The fever was accompanied by peripheral aches and pains followed by the gradual development of a cough and yellow sputum with dyspnea on exertion. The highest recorded temperature was 39.9°C 3 days before admission, with worsening cough and sputum; therefore, he visited an outpatient clinic. Test results showed the following: white blood cells, 42.12 × 10⁹/L; hemoglobin, 122 g/L; platelets, 1424 × 10⁹/L; and C-reactive protein, 311.4 mg/L. Chest computed tomography suggested multiple infectious foci in both lungs, predominantly in the lower lobe of the right lung; mild pleural effusion on the right side; and multiple lymph nodes in the mediastinum, some of which were slightly enlarged. Following admission, L. pneumophila IgM antibody titers were 0.56, 1.24, and 1.31, respectively, and the oxygenation index was 151. Right lower lung palpation showed fibrillation was slightly diminished, and percussion revealed murmurs. The breath sounds were low, with coarse breath sounds heard over the left lung, and no dry rales were heard. The patient’s dyspnea worsened, and he received an oxygen mask (8 L/min) with meropenem (1.0g q8h), moxifloxacin (0.4g qd), and vancomycin (1.0 g q12h) for treating the infection. Bedside fiberoptic bronchoscopy showed some golden-yellow secretions in the lumen, congestion of the tracheal mucosa, and a sharp, central bulge. Second-generation sequencing of plasma and bronchoalveolar lavage fluid (BALF) showed positivity for L. bozemanae. The patient gradually recovered following anti-infective treatment with rifampicin (0.45 g qd), moxifloxacin (0.4 g qd), azithromycin (0.5 g qd) and piperacillin/tazobactam (4.5 g q8h). Eventually, the patient was cured and discharged ( Figure 1 ).

The patient’s sputum sample was spread on glycine–vancomycin–polymyxin–cycloheximide plates (OXOID, UK) for pathogen isolation. The isolated strain was identified as L. bozemanae by 16S rRNA gene sequencing and next-generation sequencing. Evaluation of phylogenetic trees based on gene families ( Figure 2A ) and core genes ( Figure 2B ) showed that L. bozemanae BOZE (ICDC) was most closely related to L. bozemanae 94163278 ( Supplementary Data Sheets S1 and S2 ). Whole genome sequencing data have been deposited in the NCBI BioProject repository (accession no. PRJNA992381) and the BioSample database (accession no. SAMN36348289).

An understanding of the biological features of bacteria can provide a solid basis for infection treatment. At present, 17% environmental and clinical Legionella species in China have been found to exhibit azithromycin resistance (Jia et al., 2019). Therefore, the sensitivity of L. bozemanae BOZE (ICDC) to nine representative antibiotics (ciprofloxacin, levofloxacin, moxifloxacin, erythromycin, azithromycin, clarithromycin, rifampicin, tigecycline and doxycycline) was tested, and it was found that the minimum inhibitory concentration values were significantly lower than the epidemiological cut-off values ( Table 1 ). Thus, routine clinical medications can be used to treat Legionnaires’ disease caused by L. bozemanae BOZE (ICDC). Cytologic experiments showed that the fold change in growth over T0 of L. pneumophila ATCC 33152 and L. bozemanae BOZE(ICDC) was overall higher than that of JR32 at T24, T48, and T72 hours. And similar intracellular proliferative capacity compared to the highly pathogenic and virulent L. pneumophila ATCC 33152 suggests the need to be vigilant about the infection of L. pneumophila BOZE (ICDC) ( Figure 2C ).

In summary, we reported a rare case of Legionnaires’ disease caused by the rare L. bozemanae in China. Our findings highlight that clinicians should be aware that infection with this species may go undetected in patients with clinical pneumonia, and they should particularly consider Legionella infection in immunocompromised patients. In addition, the surveillance and investigation of L. bozemanae in aquatic environments should be strengthened to prevent and control the outbreak of Legionnaires’ disease caused by L. bozemanae.