Characteristics of Patients with Idiopathic Bronchiectasis in Comparison to Post-infectious Bronchiectasis in South Korea
Article information
, Hyun Lee2, Hayoung Choi3, Seung Won Ra4, Yeon-Mok Oh,5, KMBARC investigators and Korean Bronchiectasis Study GroupAbstract
Background
Bronchiectasis has a complex and heterogeneous pathogenesis, with various etiologies, the majority being idiopathic. This study aimed to examine the characteristics of patients with idiopathic bronchiectasis in comparison to those with post-infectious bronchiectasis.
Methods
We analyzed data from patients with idiopathic and post-infectious bronchiectasis (including post-tuberculosis) from the Korean Multicenter Bronchiectasis Audit and Research Collaboration (KMBARC) registry, a prospective cohort study.
Results
Among the 866 patients enrolled in the study, 346 (40.0%) were classified as having idiopathic bronchiectasis, while 363 (41.9%) had post-infectious bronchiectasis. The idiopathic group demonstrated a shorter disease duration, a higher body mass index (BMI), a lower prevalence of chronic obstructive pulmonary disease (COPD), a higher prevalence of rhinosinusitis, a predominance of lower lobe distribution, less frequent use of regular respiratory treatments, better pulmonary function, and a statistically lower bronchiectasis severity index compared to the post-infectious group. A multivariable logistic regression analysis was conducted, considering factors such as gender, age, BMI, history of asthma, COPD, rhinosinusitis, rheumatoid arthritis, gastroesophageal reflux disease, and smoking status. A higher BMI (odds ratio [OR], 1.09; 95% confidence interval [CI], 1.04 to 1.15) and a history of rhinosinusitis (OR, 3.10; 95% CI, 1.57 to 6.14) were associated with idiopathic bronchiectasis. In contrast, a history of COPD was linked to post-infectious bronchiectasis (OR, 0.57; 95% CI, 0.41 to 0.80).
Conclusion
Patients with idiopathic bronchiectasis are characterized by a higher BMI and a history of rhinosinusitis compared to those with post-infectious bronchiectasis. These findings may provide exploratory insights into underlying systemic or non-pulmonary factors. Further research is necessary to clarify the clinical significance of these associations.
Introduction
Bronchiectasis has long been regarded as an ‘orphan’ disease, often overlooked by respiratory physicians. However, recent studies indicate that its prevalence is increasing worldwide [1-4], posing a significant burden on public health [5-7]. In South Korea, several studies have reported a prevalence of 464 per 100,000 and highlighted the disease’s impact [8-10].
Bronchiectasis has a complex and heterogeneous pathogenesis, typically resulting from a variety of underlying etiologies. Among these, idiopathic bronchiectasis— where no clear cause is identified—is one of the most common types globally. According to international registries, the proportion of idiopathic bronchiectasis is 41% in South Korea, 29% in Australia, 42% in Europe, and 21% in India [11]. In the Korean, Australian, and European registries, idiopathic bronchiectasis was identified as the most prevalent cause.
Asians exhibit a higher prevalence of bronchiectasis compared to other races [12-14], making research into bronchiectasis and its common causes in the Asian region essential. However, knowledge about idiopathic bronchiectasis in Asia remains limited due to a scarcity of studies on the topic.
In our study, we compared idiopathic bronchiectasis with post-infectious bronchiectasis, which includes cases resulting from both tuberculosis (TB) and non-TB infections. These two groups represent the majority of cases in our cohort. By focusing on a single major etiological group (post-infectious) as a comparator, we ensured a more homogeneous analysis instead of comparing various diverse etiologies.
Thus, the aim of our study was to investigate the characteristics of idiopathic bronchiectasis in Korean patients, in comparison with post-infectious bronchiectasis in South Korea, laying the foundation for further targeted research.
Materials and Methods
1. Study design and participants
This comparative study examines idiopathic and post-infectious bronchiectasis using baseline data from the Korean Multicenter Bronchiectasis Audit and Research Collaboration (KMBARC) [15]. KMBARC is a prospective, non-interventional observational cohort study focused on bronchiectasis in South Korea. Participants were enrolled in the KMBARC registry from August 21, 2018, to July 9, 2021. In this study, bronchiectasis was defined as the presence of bronchodilation in at least one lobe as observed on chest computed tomography (CT). The exclusion criteria included: (1) bronchiectasis due to cystic fibrosis; (2) age under 18 years; (3) traction bronchiectasis associated with interstitial lung disease; (4) patients actively treated for pneumonia, pulmonary TB, or non-tuberculous mycobacterial (NTM) infection; (5) patients unable or unwilling to provide informed consent; (6) pregnant patients; and (7) patients who had undergone lung resection or cardiopulmonary transplantation. Detailed registry protocols and baseline characteristics of the patients were described in previous studies [11,15].
A total of 938 patients from the registry were enrolled, with 72 patients excluded due to unknown etiology (62 patients) or inability to classify (10 patients) (Figure 1). Patients with multiple etiologies were excluded to facilitate a clear comparison between distinct etiological groups, except for those with both post-infectious and post-TB etiologies, who were classified as post-infectious since these groups were combined for analysis.
Flow chart of the selection process of patients. CT: computed tomography.
We defined post-infectious bronchiectasis as having any respiratory infection, including TB, as the underlying etiology. Among the remaining 866 patients, 346 were identified as having idiopathic bronchiectasis, 363 had post-infectious bronchiectasis, and 157 patients had other identified etiologies.
2. Ethical statement
The study was approved by the Institutional Review Board of Asan Medical Center (approval no. S2021-2503-0001), and written informed consent was obtained from all participants.
3. Definition of idiopathic bronchiectasis
The etiology of bronchiectasis was determined by the attending physicians based on diagnostic assessments using standardized questionnaires and laboratory tests [15]. These assessments were consistently conducted following the European Bronchiectasis Registry (EMBARC) protocol [16]. The considered etiologies include idiopathic, post-infectious, post-TB, allergic bronchopulmonary aspergillosis, rheumatoid arthritis, connective tissue disease, inflammatory bowel disease, aspiration, gastroesophageal reflux disease (GERD), NTM pulmonary disease, chronic obstructive pulmonary disease (COPD), asthma, primary ciliary dyskinesia, Kartagener’s syndrome, Young’s syndrome, α-1 antitrypsin deficiency, common variable immunodeficiency, X-linked agammaglobulinaemia, immunoglobulin A deficiency, immunoglobulin G subclass deficiency, specific antibody deficiency, human immunodeficiency virus infection, Williams-Campbell syndrome, Marfan syndrome, Mounier-Kuhn syndrome, yellow nail syndrome, human T-lymphotropic virus type 1 infection, infant chronic lung disease, mechanical ventilation in newborn infants, and pink disease. Physicians had the flexibility to select multiple etiologies or identify a specific etiology not listed among the suggested options.
4. Assessments of patients’ characteristics
Age was calculated by subtracting the year of birth from the date of consent. The duration of bronchiectasis was defined as the interval between the first diagnosis date and the date of study enrollment. Body mass index (BMI) was calculated by dividing weight (in kilograms) by the square of height (in meters squared). Dyspnea was assessed using the modified Medical Research Council (mMRC) dyspnea scale. Comorbidities, including asthma, COPD, rhinosinusitis, rheumatoid arthritis, and GERD, were determined through physician diagnosis.
Regarding radiology, the severity of dilatation and the number of involved lobes were evaluated using chest CT. To assess the severity of bronchiectasis, the modified Reiff score was employed [17]. Lobe dominance in bronchiectasis distribution was determined by comparing the sum of the modified Reiff scores assigned to each lobe (cylindrical=1, varicose=2, cystic=3). The sums for the left upper lobe and right upper lobe, lingula and right middle lobe, and left lower lobe and right lower lobe were calculated, respectively. If the sum of the modified Reiff scores for both upper lobes was the highest, it was classified as upper lobe dominance. Similarly, middle lobe dominance and lower lobe dominance were defined in the same manner, with the lingula considered as the left middle lobe. In cases where the scores were equal, it was classified as having no lobe dominance. Data with ‘unknown severity’ were excluded from the analysis.
We collected data on whether patients were undergoing regular respiratory treatment. For those receiving treatment, we further inquired about the specific types of drugs, including: (1) respiratory medications: long-acting muscarinic antagonists (LAMA), inhaled corticosteroids (ICS), long-acting β2 agonists (LABA), ICS/LABA combinations, LAMA/LABA combinations, intravenous immunoglobulin, itraconazole, leukotriene receptor antagonists (LTRA), long-term (≥28 days) use of oral steroids, monoclonal antibodies, mucolytics, or nebulized bronchodilators; (2) antibiotics: inhaled antibiotics, long-term (≥28 days) use of oral antibiotics, or systemic antibiotics; (3) physiotherapy or mucoactive treatment, including nebulized saline, nebulized hypertonic saline, sodium hyaluronate, nebulized mannitol, or DNase. For analysis, we included treatment modalities applied by more than 10% of the patient population, which were ICS/LABA, LTRA, LAMA, LABA/LAMA combinations, mucolytics, and cyclical antibiotic therapy.
5. Assessments of bronchiectasis severity and the previous exacerbations
Prebronchodilator and/or postbronchodilator spirometry was performed according to the criteria established by the American Thoracic Society and the European Respiratory Society [18]. The percentages for forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) were calculated using reference equations for the Korean population [19]. Total lung capacity (TLC) data were also collected when available, and the percentage for TLC was calculated using the European Community for Steel and Coal (ECSC) equation, which has been identified as the most suitable for Koreans in a previous study [20].
The clinical data on previous exacerbations that required outpatient visits in the year prior to study enrollment were collected. A consensus definition of acute exacerbations of bronchiectasis was used [21]. Acute exacerbations are defined as a deterioration in at least three of the following symptoms for a minimum of 48 hours: (1) cough; (2) increased sputum volume and/or consistent changes; (3) sputum purulence; (4) dyspnea and/or exercise intolerance; (5) fatigue and/or malaise; and (6) hemoptysis. Information regarding respiratory- related emergency room (ER) visits or hospitalizations in the previous year was also collected.
Microbiological profiles were obtained from respiratory specimens, such as spontaneous sputum or lower respiratory specimens (induced sputum, bronchoalveolar lavage, or nasopharyngeal swab), when the patient was in a clinically stable condition.
The severity of bronchiectasis was evaluated using the bronchiectasis severity index (BSI) [22]. Additionally, quality of life was measured with the Korean version of the bronchiectasis health questionnaire (BHQ) score [23].
6. Statistical analyses
Categorical variables are presented as percentages of patients, with p-values calculated using the chi-squared test. Continuous variables underwent normality testing (Kolmogorov-Smirnov test). Those with a normal distribution are presented as mean and standard deviation, with p-values calculated using the independent t-test. Variables that did not have a normal distribution are presented as median and interquartile range (IQR), with p-values calculated using the Mann-Whitney U test.
Multivariable logistic regression analysis was performed to identify factors related to idiopathic bronchiectasis in comparison to post-infectious bronchiectasis. The multiple logistic regression model included gender, age, BMI, comorbidities (asthma, COPD, rhinosinusitis, rheumatoid arthritis, GERD), and smoking status. These factors were selected a priori based on their clinical plausibility as potential causative factors for bronchiectasis rather than as consequences of the disease.
All statistical analyses were conducted using SPSS Statistics for Windows version 27 (IBM Corp., Armonk, NY, USA).
Results
1. Patients’ characteristics
Of the 866 patients enrolled in this study, the etiology of 346 (40.0%) was idiopathic bronchiectasis, while 363 (41.9%) had post-infectious bronchiectasis (Table 1). In the idiopathic group, 55.8% were female, compared to 53.0% in the post-infectious group. The average ages were 65.0 years for the idiopathic group and 64.8 years for the post-infectious group.
Characteristics of patients
The idiopathic group had a significantly higher proportion of patients with a shorter disease duration of bronchiectasis (p=0.001) and a higher BMI (mean±standard deviation, 23.5±3.4 kg/m2 vs. 22.5±3.6 kg/m2, p<0.001) compared to the post-infectious group.
Among the comorbidities, the idiopathic group exhibited a lower proportion of COPD (29.5% vs. 42.1%, p<0.001) and a higher proportion of rhinosinusitis (10.1% vs. 3.6%, p=0.001). There was a significant difference in the lobe dominance of bronchiectasis distribution (p=0.001), with the idiopathic group showing a higher percentage of lower lobe dominance (41.4% vs. 34.4%, p=0.058) and a lower percentage of upper lobe dominance (6.0% vs. 14.1%, p<0.001) compared to the post-infectious group.
Regarding respiratory medications, the idiopathic group had a significantly lower percentage receiving regular treatment (67.5% vs. 74.7%, p=0.037). Specifically, there were significant differences in the usage of LABA/LAMA and mucolytics, with lower percentages in the idiopathic group (LABA/LAMA, 39.1% vs. 48.2%, p=0.045; mucolytics, 59.0% vs. 71.3%, p=0.003).
There were no significant differences between the idiopathic and post-infectious bronchiectasis patients regarding mMRC dyspnea score, prevalence of asthma, rheumatoid arthritis, GERD, or smoking status.
2. Factors related to bronchiectasis severity
Regarding the pulmonary function tests, the idiopathic group demonstrated significantly higher FEV1 (67.6%±19.4% vs. 60.8%±19.1%, p<0.001) and FVC (75.3%±15.4% vs. 70.1%±16.5%, p<0.001) compared to the post-infectious group (Table 2). The FEV1/FVC ratio was also higher in the idiopathic group (0.69 [IQR, 0.59 to 0.77] vs. 0.66 [IQR, 0.56 to 0.74], p=0.015); however, the proportion of patients with an FEV1/FVC ratio lower than 0.7 did not show statistically significant differences (53.3% vs. 60.1%, p=0.084). Additionally, TLC data were collected from 161 patients (80 idiopathic, 81 post-infectious), with TLC being significantly higher in the idiopathic group (97.5% [IQR, 87.7 to 102.3] vs. 89.4% [IQR, 80.6 to 98.5], p=0.003). The BSI was significantly lower in the idiopathic group compared to the post-infectious group (6 [IQR, 4 to 8] vs. 6 [IQR, 5 to 9], p=0.011).
Factors related to bronchiectasis severity
There were no significant differences between the two groups regarding the number of exacerbations requiring outpatient visits in the previous year, the number of respiratory-related ER visits or hospital admissions in the previous year, the proportion of Pseudomonas aeruginosa isolation, and the BHQ score.
3. Factors related to idiopathic bronchiectasis in
comparison to post-infectious bronchiectasis Using multivariable logistic regression analysis, we identified several factors associated with idiopathic bronchiectasis compared to post-infectious bronchiectasis (Table 3). These factors included a higher BMI (odds ratio [OR], 1.09; p<0.001) and a history of rhinosinusitis (OR, 3.10; p=0.001). In contrast, a history of COPD was linked to the post-infectious group (OR, 0.57; p=0.001). Other factors, such as gender, age, history of asthma, rheumatoid arthritis, GERD, and smoking status, did not demonstrate statistically significant associations.
Factors related to idiopathic bronchiectasis in comparison with post-infectious bronchiectasis
Discussion
In this multicenter observational study, we identified several distinctive features of idiopathic bronchiectasis compared to post-infectious bronchiectasis. The idiopathic group had a shorter disease duration, a higher BMI, a lower prevalence of COPD, a higher prevalence of rhinosinusitis, a predominant lower lobe distribution, reduced use of regular respiratory treatment, better pulmonary function, and a lower BSI. However, no statistically significant differences were found in exacerbation rates, P. aeruginosa isolation, or quality of life as measured by the BHQ score.
To clarify the differences among bronchiectasis etiologies, we conducted additional subgroup analyses comparing idiopathic bronchiectasis, post-infectious bronchiectasis (non-TB infection), and post-TB bronchiectasis separately (Supplementary Tables S1, S2). Ten patients were excluded from these analyses due to overlapping etiologies. Most factors remained consistent with the primary analysis, which compared idiopathic bronchiectasis to the broader post-infectious group (including both TB and non-TB infections). However, certain variables showed notable differences in statistical significance in the subgroup analyses.
We found no significant difference in disease duration between idiopathic and post-TB bronchiectasis, indicating that the initial observed difference in disease duration between idiopathic and the broader post-infectious group was primarily due to the longer duration seen in non-TB post-infectious patients. Conversely, BMI did not significantly differ between idiopathic and non-TB post-infectious bronchiectasis groups, suggesting that the BMI difference was mainly driven by the idiopathic versus post-TB comparison. Asthma prevalence was significantly higher in the non-TB post-infectious group compared to the idiopathic group, while the distinct lobe distribution differences were primarily due to upper lobe predominance in the post-TB bronchiectasis group. Additionally, the post-TB bronchiectasis group had significantly higher rates of medication use and higher BSI scores compared to the idiopathic group, whereas the non-TB post-infectious group did not show such differences.
The relatively better pulmonary function observed in patients with idiopathic bronchiectasis can be partially explained by the notably poorer pulmonary outcomes typically associated with post-TB bronchiectasis. Post-TB bronchiectasis often affects the upper lobes, where symptoms tend to develop insidiously, leading patients to seek medical attention only after significant pulmonary deterioration has occurred. Consequently, the broader post-infectious bronchiectasis group, which includes post-TB cases, naturally demonstrates worse pulmonary function. Since post-TB bronchiectasis has distinct anatomical and clinical characteristics that may differentiate it from other infectious causes, this heterogeneity within the ‘post-infectious’ group may have influenced group comparisons.
We conducted a multivariable logistic regression analysis with factors expected to contribute to the development of bronchiectasis, including gender, age, BMI, asthma, COPD, rhinosinusitis, rheumatoid arthritis, GERD, and smoking status. Our results indicated that a higher BMI and a history of rhinosinusitis were associated with the idiopathic group, while a history of COPD was associated with the post-infectious group. Furthermore, when we included the Charlson comorbidity index in the multivariable analysis, the same results were observed (Supplementary Table S3).
Our findings are significant as this is the first large-scale study exclusively examining idiopathic bronchiectasis in South Korea, involving a diverse patient cohort from referral university hospitals. Given that idiopathic bronchiectasis is the most common etiology in South Korea [1], these results provide foundational insights and encourage future research.
Our study revealed a higher BMI in the idiopathic group compared to the post-infectious group. Specifically, patients in the idiopathic group had a significantly higher weight (median 58 kg [IQR, 52 to 65] vs. 56.9 kg [IQR, 50 to 65], p=0.037) and shorter height (158.4 cm [IQR, 153 to 166] vs. 160 cm [IQR, 155 to 167.95], p=0.039) (Supplementary Table S4). The difference in BMI was notable when analyzed by gender. In males, the idiopathic group had a higher BMI (23.7±3.4 kg/m2 vs. 22.6±3.7 kg/m2, p=0.008) and a significantly shorter height (166 cm [IQR, 161 to 170] vs. 168 cm [IQR, 161 to 173], p=0.037), although weight did not differ significantly (64.9±9.46 kg vs. 63.4±11.5 kg, p=0.2). In females, the idiopathic group also exhibited a higher BMI (23.3±3.3 kg/m2 vs. 22.5±3.4 kg/m2, p=0.013) with a significant difference in weight (55.4±8.0 kg vs. 53.5±8.2 kg, p=0.032), while height remained comparable between the groups (154 cm [IQR, 151 to 158] vs. 155 cm [IQR, 150 to 159], p=0.4).
We propose that the differences in BMI may reflect systemic or developmental factors that indirectly contribute to the pathogenesis of bronchiectasis. Unlike post-infectious bronchiectasis, which clearly arises from prior pulmonary infections, idiopathic bronchiectasis may have systemic or developmental origins. These systemic influences could originate early in life or even prenatally, potentially affecting the development of bronchiectasis through indirect mechanisms.
The study conducted in Spain found no significant differences in BMI between the idiopathic and post-infectious groups. However, it did observe a significantly higher BMI when comparing the idiopathic group to all known etiologies collectively [24] (Supplementary Table S5). While it is important to consider ethnic and metabolic differences across populations when interpreting these findings, most international studies have either not included BMI in their etiology comparisons or have not demonstrated statistically significant differences. This limitation affects our ability to make comprehensive cross-ethnic comparisons. Nevertheless, the trend toward a higher BMI in idiopathic bronchiectasis has been observed in both the Spanish cohort and our study.
Also, our study found that the prevalence of rhinosinusitis was significantly higher in the idiopathic group than in the post-infectious group, consistent with previous studies [24-26]. A study conducted in Belgium indicated a high prevalence of rhinosinusitis in both the idiopathic and primary ciliary dyskinesia groups, suggesting a connection to upper airway dysfunction in these populations [26]. The association between idiopathic bronchiectasis and rhinosinusitis may be attributed to undiagnosed primary ciliary dyskinesia or cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction. However, due to the limitations of genetic information in our current study, we were unable to investigate this directly. We recommend future comprehensive genetic evaluations to further explore these associations.
The idiopathic group exhibited a slightly higher proportion of females, which is consistent with previous studies [24,26-29]; however, this difference did not achieve statistical significance. Several studies have similarly found no significant association between etiology and gender [25,30,31].
There was no statistically significant difference in age between the two groups. Some previous studies reported a younger age in the idiopathic group compared to the post-infectious group [24,31]. Additionally, the age at diagnosis varied among studies, with research from Spain, France, and Taiwan noting a younger age at diagnosis in the idiopathic group [24,27,29], while studies from England reported an older age at diagnosis [25]. Although our data did not include specific information on age at diagnosis, the shorter disease duration observed in the idiopathic group suggests a potentially older age at diagnosis compared to the post-infectious group.
This study aligns with previous research on pulmonary function [24,27,29,32] and severity [28,31,33]. The idiopathic group demonstrated significantly higher FEV1 and a lower BSI, suggesting better pulmonary function and reduced severity. However, despite the significant difference in BSI (p<0.05), the identical median values (idiopathic 6 [IQR, 4 to 8], post-infectious 6 [IQR, 5 to 9]) and small differences in IQR limit the clinical interpretation in real-world settings. Nevertheless, there was consistency with other measures indicating milder severity in idiopathic bronchiectasis compared to the post-infectious group. Notably, a study conducted within the Chinese Han population found no significant correlation between bronchiectasis etiology and pulmonary function or severity [30].
The idiopathic group predominantly exhibited lower lobe bronchiectasis, consistent with previous reports. A study conducted in England found that this group primarily displayed symmetrical bilateral bronchiectasis in the lower lobes [25]. The inclusion of the post-TB group (179 patients) in the post-infectious group likely influenced these distribution findings, reflecting the upper lobe predominance associated with TB. Furthermore, other studies indicated that the idiopathic group demonstrated more bilateral involvement compared to the post-infectious group [24] and more extensive lobe involvement compared to the post-TB group [31].
The regular use of respiratory medications was more prevalent in the post-infectious bronchiectasis group compared to the idiopathic group. This difference may be influenced by several factors, including lower healthcare utilization, delayed diagnosis, or insufficient symptom recognition by physicians and patients in the idiopathic group. However, the data indicate that disease severity is a primary driver. This is supported by the subgroup analysis (Supplementary Table S2), which shows a clear stepwise increase in medication use (specifically LABA/LAMA) corresponding to the rising severity from idiopathic to post-infectious and finally to post-TB cohorts.
While prior research often regarded COPD as a cause of bronchiectasis, our study classified COPD as a comorbidity. We found that COPD was associated with post-infectious bronchiectasis rather than idiopathic bronchiectasis, although no significant association was observed between smoking status and bronchiectasis etiology. Earlier studies have indicated that bronchiectasis related to COPD is associated with more severe disease [28,33].
No significant differences were observed in P. aeruginosa isolation rates in our study. Previous research on the association between P. aeruginosa isolation and bronchiectasis etiologies has produced variable results. Some studies reported no significant differences [25,30,32], while others indicated reduced P. aeruginosa isolation or lower chronic bronchial infection caused by P. aeruginosa in idiopathic groups [24,27,29,33]. In contrast, research conducted in Saudi Arabia reported significantly higher P. aeruginosa isolation rates in the idiopathic group [31]. Despite variations in BMI and treatment usage, exacerbation rates and microbiological profiles did not show significant differences. This may be due to the limited sample size, which could hinder the detection of differences. It may also suggest that the low overall exacerbation rate in this cohort (with over 80% reporting no exacerbation) reflects under-recognition within the group. Additionally, it is plausible that once irreversible structural damage occurs, the shared pathophysiology of bronchiectasis—rather than the initial etiology—becomes the primary driver of exacerbations.
Our study has several limitations to consider. First, idiopathic bronchiectasis presents significant diagnostic and interpretative challenges due to uncertainties surrounding its etiology and the limited existing epidemiological data. Variations between centers and clinicians may have influenced diagnostic accuracy, particularly because the classification of idiopathic cases and the diagnosis of comorbidities, such as rhinosinusitis, relied on physician reporting, which is inherently subjective. To mitigate these limitations, we implemented a standardized classification for bronchiectasis etiology to reduce variability and enhance consistency across participating centers [16]. Nevertheless, as idiopathic bronchiectasis is a diagnosis of exclusion, the potential for misclassification remains a significant diagnostic limitation. Second, patients were primarily recruited from secondary or tertiary centers, which may have selected for more severe cases. Third, while the registry was a prospective cohort, our study analyzed only baseline data, giving it a retrospective nature with potential recall bias, particularly regarding childhood infections. This may have led to an overestimation of the idiopathic group and, crucially, may have diluted the true differences between the etiological cohorts, potentially influencing our findings. Finally, since this study utilized cross-sectional data analysis, it was inherently limited in establishing causality and fully adjusting for potential confounding variables. Therefore, our findings should be considered exploratory, underscoring the need for prospective longitudinal and mechanistic studies to clarify these associations.
Despite these limitations, our study possesses considerable strengths as the first large-scale investigation of bronchiectasis etiology conducted in South Korea. Additionally, several findings align with international studies, supporting their validity and generalizability. Although our study could not directly prove causality or elucidate the pathophysiological mechanisms, it highlighted notable associations of idiopathic bronchiectasis that warrant further exploration in prospective studies.
In conclusion, the idiopathic bronchiectasis group shows a higher BMI and a greater history of rhinosinusitis compared to the post-infectious group. These exploratory associations may indicate underlying systemic or non-pulmonary factors rather than defining direct clinical features. Future research, including prospective longitudinal studies that assess early-life exposures and conduct comprehensive multi-omics analyses to explore biomarkers and mechanisms, is crucial before these findings can significantly enhance clinical practice, such as improving diagnosis, prognostication, or management strategies. Additionally, comparisons with international bronchiectasis registries, like EMBARC and other global cohorts, are necessary to further contextualize and validate our findings.
Notes
Authors’ Contributions
Conceptualization: Hwang SY, Lee H, Choi H, Ra SW, Oh YM. Methodology: Hwang SY, Lee H, Oh YM. Formal analysis: Hwang SY, Oh YM. Data curation: Hwang SY. Software: Hwang SY. Validation: Hwang SY, Lee H, Choi H, Ra SW, Oh YM. Investigation: Hwang SY, Lee H, Choi H, Ra SW, Oh YM. Writing - original draft preparation: Hwang SY. Writing - review and editing: Hwang SY, Lee H, Choi H, Ra SW, Oh YM. Approval of final manuscript: all authors.
Conflicts of Interest
Seung Won Ra is an associate editor of the journal, but he was not involved in the peer reviewer selection, evaluation, or decision process of this article. No other potential conflicts of interest relevant to this article were reported.
Acknowledgments
The authors thank all members of the Korean Multicenter Bronchiectasis Audit and Research Collaboration (KMBARC) registry.
Funding
No funding to declare.
Supplementary Material
Supplementary material can be found in the journal homepage (http://www.e-trd.org).
Subgroup analysis of patient characteristics among idiopathic, post-infectious (non-TB infection), and post-TB bronchiectasis.
Subgroup analysis of factors related to bronchiectasis severity among idiopathic, post-infectious (non-TB infection), and post-TB bronchiectasis.
Factors related to idiopathic bronchiectasis in comparison with post-infectious bronchiectasis (including Charlson comorbidity index).
Comparison of BMI, weight, and height between idiopathic and post-infectious bronchiectasis groups.
Comparison of the findings in other studies regarding idiopathic bronchiectasis.