This study identified the characteristics and risk factors for developing a post-bronchoscopy respiratory infection. A total of 6.1% of all patients developed post-bronchoscopy respiratory infections, and the risk factors were high WBC counts or CRP levels, low serum albumin levels, necrosis and/or a cavity in the tumor, and large tumor diameter. However, these risk factors differ from those in past reports [6, 9]. We developed a predictive score that included necrosis and/or a cavity in the tumor, tumor diameter ≥30 mm, and serum albumin <4.0 g/dL. A score of a least 2 was a good predictor for developing a post-bronchoscopy respiratory infection. In total, 60% of the patients with post-bronchoscopy respiratory infections showed lung abscesses. The incidence of developing lung abscesses after bronchoscopy has increased in recent years. We believe that these different risk factors are caused by the advancement of bronchoscopic techniques.
A past report from 2012 to 2013 suggested risk factors for post-bronchoscopy respiratory infection, such as an elderly age, current smoking status, and central location of the tumor . However, these factors did not differ significantly between the infection group and the noninfection group in our study. These differences might be caused by the increasing incidence of lung abscesses after bronchoscopy since the bronchoscopic techniques have been changed. Generally, lung abscesses are rare in post-bronchoscopy respiratory infections and occur in 0.22-1.06% of the patients [7, 8]. Similar to the percentage in past reports, 0.8% of the patients in our study had lung abscesses after bronchoscopy in 2013, when EBUS-GS was not yet used in our hospital. However, the incidence of lung abscesses after bronchoscopy increased to as high as 5.3% in 2019. Recently, the EBUS-GS technique has been used and has significantly increased the diagnosis rate of peripheral pulmonary lesions [15, 16]. Moreover, the number of TBLB procedures performed is higher because the specimens from EBUS-GS are smaller in size than those from routine TBLB . The British Thoracic Society guidelines for bronchoscopy recommend taking at least five biopsy samples , and an additional ﬁve bronchial forceps biopsies should be considered for phenotyping and genotyping exams . In our hospital, the number of biopsy by bronchoscopy procedures performed increased from October 2018 because of phenotyping and genotyping, and the number of biopsies performed by bronchoscopy was significantly greater in 2019 than in 2017. Therefore, we thought that post-bronchoscopy lung abscesses can easily occur due to the type of approach, infection of the central tumor using EBUS-GS and increases in the number biopsies performed.
Lung abscesses are a type of liquefaction of the lung tissue and a formation of cavities containing necrotic debris or fluid caused by microbial infection . Ishida M et al. reported that a risk factor for post-bronchoscopy lung abscess was a tumor diameter of 30 mm or more , which is similar to our report. We demonstrated risk factors such as necrosis and/or a cavity in the tumor and large tumor diameter. Conversely, all patients with post-obstructive pneumonia showed abnormal bronchoscopic findings and did not show necrosis and/or cavities in the tumors. Patients with typical pneumonia after bronchoscopy did not show necrosis, a cavity in the tumor or abnormal bronchoscopic findings. Therefore, the risk factors for post-bronchoscopy respiratory infection might differ among types of infection.
Other risk factors for post-bronchoscopy respiratory infection were low serum albumin before the bronchoscopic examination and PD-L1 expression in tumor cells. Low serum albumin might indicate that the immune systems of the patients in the infection group were worse than those of the patients in the noninfection group. Generally, the nutritional status as assessed by the serum albumin level relates to the immune response, and malnutrition is a common cause of immunodeficiency [19, 20]. In addition, PD-L1 expression in tumor cells is related to the immune system. The combination of programmed cell death 1 (PD-1) and PD-L1 leads to tumor immune evasion through the suppression of T cells , and the role of PD-1 is to regulate infections due to the limited function of macrophages as well as the T cell-independent B cell response . A case report of a patient with a lung abscess after bronchoscopy showing high levels of PD-L1 was previously published . Thus, immune disorder is an important risk factor for the development of post-bronchoscopy respiratory infections.
The British Thoracic Society guidelines for bronchoscopy do not recommend antibiotic prophylaxis before bronchoscopy for endocarditis, fever, or pneumonia . In our study, antibiotic prophylaxis did not effectively prevent post-bronchoscopy respiratory infections. However, very few patients received antibiotic prophylaxis, so whether antibiotic prophylaxis was useful cannot be determined. Kanazawa H et al. reported that azithromycin was effective as prophylactic antibiotherapy in preventing infections post bronchoscopy compared to the no-treatment group (3.0% vs 14.8%, p=0.02) . Generally, the common causative organisms of lung infections after bronchoscopy are oro- or nasopharyngeal microbes, such as Streptococcus, Staphylococcus, Moraxella, Neisseria, and anaerobic bacterial species . Therefore, prophylactic antibiotherapy might be better adapted to anaerobic bacteria. Many patients with post-bronchoscopy respiratory infections canceled their planned oncologic treatments , and some post-bronchoscopy respiratory infections could not improve with antibiotics and required surgical invention . Therefore, prophylactic antibiotherapy might be necessary for high-risk patients. A prospective study of effective antibiotic prophylaxis is required.
This investigation had several limitations. The study was conducted retrospectively in a single center. The target disease was lung cancer; therefore, the incidence in this study does not represent the overall incidence of bronchoscopy. Some medical data were not recorded. Some patients received prophylaxis antibiotherapy. We reviewed all types of infections together. Some patients did not have PD-L1 tumor cell expression data because the analysis was not requested or sample size from TBLB was too small.