Lung transplantation in children

Lung transplantation is a well-established treatment for children facing advanced lung disease and pulmonary vascular disorders. However, organ shortage remains highest in children. For fitting the small chest of children, transplantation of downsized adult lungs, lobes, or even segments were successfully established. The worldwide median survival after pediatric lung transplantation is currently 5.7 years, while under consideration of age, underlying disease, and peri- and posttransplant center experience, median survival of more than 10 years is reported. Timing of referral for transplantation, ischemia-reperfusion injury, primary graft dysfunction, and acute and chronic rejection after transplantation remain the main challenges.

Impact of extended sinus surgery on allograft infection, allograft function and overall survival in cystic fibrosis lung transplant recipients

BACKGROUND

Studies investigating the impact of sinus surgery for cystic fibrosis (CF) patients performed early after lung transplantation (Ltx) are scarce. Recent studies evaluating frequency of respiratory infections and graft outcomes are not available.

OBJECTIVES/HYPOTHESIS

To determine whether there is a difference in allograft infection, allograft function and overall survival among CF lung transplant recipients with and without concomitant sinus surgery.

STUDY DESIGN

Retrospective single-center study.

METHODS

We examined 71 CF patients who underwent Ltx between 2009 and 2019 at our center. Fifty-nine patients had sinus surgery before or/and after transplantation and twelve did not undergo sinus surgery. We assessed the survival, the diagnosis of chronic allograft dysfunction (CLAD) and all elevated (> 5 mg/l) c-reactive protein episodes during the observed period. The infectious events of the upper and lower airways were categorized in mild infections (5-15 mg/l CRP) and severe infections (> 15 mg/l CRP).

RESULTS

There was no difference in the long-time overall survival (p = 0.87) and no benefit in the short-term survival at 4 year post-transplant (p = 0.29) in both groups. There was no difference in both groups concerning CLAD diagnosis (p = 0.92). The incidence of severe upper and lower airway infections (CRP > 15 mg/l) was significantly decreased in the sinus surgery group (p = 0.015), whereas in mild infections there was a trend to decreased infections in the sinus surgery group (p = 0.056).

CONCLUSIONS

CF patients undergoing Ltx benefit from extended endoscopic sinus surgery (eESS) in terms of frequency of severe infectious events of the upper and lower airways. There was no difference in overall survival and frequency of CLAD in the two groups.

Microbiosis in lung allotransplantation and xenotransplantation: State of the art and future perspective

The respiratory tract is known to harbor a microbial community including bacteria, viruses, and fungi. New techniques contribute enormously to the identification of unknown or culture-independent species and reveal the interaction of the community with the host immune system. The existing respiratory microbiome and substantial equilibrium of the transplanted microbiome from donor lung grafts provide an extreme bloom of dynamic changes in the microenvironment in lung transplantation (LT) recipients. Dysbiosis in grafts are not only related to the modified microbial components but also involve the kinetics of the host-graft "talk," which signifies the destination of graft allograft injury, acute rejection, infection, and chronic allograft dysfunction development in short- and long-term survival. Microbiome-derived factors may contribute to lung xenograft survival when using genetically multimodified pig-derived organs. Here, we review the most advanced knowledge of the dynamics and resilience of microbial communities in transplanted lungs with various pretransplant indications. Conceptual and analytical points of view have been illustrated along the time series, gaining insight into the microbiome and lung grafts. Future endeavors on precise tools, sophisticated models, and novel targeted regimens are needed to improve the long-term survival in these patients.

The management of cystic fibrosis chronic rhinosinusitis: An evidenced-based review with recommendations

BACKGROUND

Cystic fibrosis (CF) chronic rhinosinusitis (CRS) has emerged as a distinct diagnostic entity, unique from other endotypes of CRS in its presentation, pathophysiology, diagnosis, treatment, and outcomes. As the sinonasal health of this patient population may have broad effects on pulmonary health and quality of life, a comprehensive understanding of the diagnostic and therapeutic approach to CF CRS is essential. In recognizing recent scientific advances and unique treatment modalities specific to this challenging patient population, in this review we systematically evaluate the scientific literature and provide an evidenced-based review with recommendations (EBRR) for fundamental management principles of CF CRS.

METHODS

A systematic review of the literature was performed. Studies evaluating interventions for the management of CF CRS were included. An iterative review process was implemented in accordance with EBRR guidelines. A treatment recommendation was generated based on an assessment of the benefits, harms, and the overall grade of evidence.

RESULTS

We evaluated the published literature on 5 unique topics. Each of the following therapeutic categories was investigated explicitly for treatment outcomes in patients with CF CRS: (1) nasal saline; (2) intranasal corticosteroids (INCS); (3) topical antibiotics; (4) cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy; and (5) endoscopic sinus surgery (ESS).

CONCLUSION

Based on the currently available evidence, nasal saline, ESS, and CFTR modulators are recommended in the management of CF CRS when appropriate. INCS and topical antibiotics are options. Clinical judgment and experience are essential in caring for patients with this uniquely challenging disorder.

Achromobacter spp. in a Cohort of Non-Selected Pre- and Post-Lung Transplant Recipients

Achromobacter is an opportunistic pathogen that mainly causes chronic lung infections in cystic fibrosis (CF) patients and is associated with increased mortality. Little is known about Achromobacter spp. in the lung transplant recipient (LTXr) population. We aimed at describing rates of Achromobacter spp. infection in LTXr prior to, in relation to, and after transplantation, as well as all-cause mortality proportion in infected and uninfected LTXr. We included 288 adult LTXr who underwent lung transplantation (LTX) between 1 January 2010 and 31 December 2019 in Denmark. Bronchoalveolar lavage was performed at regular intervals starting two weeks after transplantation. Positive cultures of Achromobacter spp. were identified in nationwide microbiology registries, and infections were categorized as persistent or transient, according to the proportion of positive cultures. A total of 11 of the 288 LTXr had transient (n = 7) or persistent (n = 4) Achromobacter spp. infection after LTX; CF was the underlying disease in 9 out of 11 LTXr. Three out of the four patients, with persistent infection after LTX, also had persistent infection before LTX. The cumulative incidence of the first episode of infection one year after LTX was 3.8% (95% CI: 1.6–6.0). The incidence rates of transient and persistent infection in the first year after LTX were 27 (12–53) and 15 (5–37) per 1000 person-years of follow-up, respectively. The all-cause mortality proportion one year after LTX was 27% in the Achromobacter spp. infected patients and 12% in the uninfected patients (p = 0.114). Achromobacter spp. mainly affected LTXr with CF as the underlying disease and was rare in non-CF LTXr. Larger studies are needed to assess long-term outcomes of Achromobacter spp. in LTXr.

Comparison of endoscopic sinus surgery timing in lung transplant patients with cystic fibrosis

BACKGROUND

No studies have investigated when endoscopic sinus surgery (ESS) is best performed in lung transplant patients with cystic fibrosis (CF). We sought to examine the effects of ESS timing on pulmonary health in this population.

METHODS

A retrospective review of all adult lung transplant patients with CF who underwent ESS at our academic medical center over a near 25-year period was performed. Patients were split into two groups based on median time from lung transplantation to ESS. Twenty-three patients were included (12 ESS early and 11 ESS delayed). Outcomes included changes in pulmonary function tests (PFTs) from baseline, pre-operative to post-operative measurements, the number and duration of hospitalizations for pulmonary exacerbations, and the number of antibiotic courses used specifically to treat pulmonary exacerbations during the 12 months before and after ESS.

RESULTS

Baseline demographics, operative history, and pulmonary function characteristics were similar between groups. While the ESS early group saw significant improvement from pre-operative percent predicted FEV₁ (ppFEV₁ ) at 12 months post-operatively (CI: 0.729 - 11.452, P = 0.030), there were no significant post-operative PFT changes for the ESS delayed group. Post-operative improvement in FEV₁ and ppFEV₁ at 12 months was significantly higher for the ESS early group relative to the ESS delayed group (CI: 0.010 - 0.583, P = 0.043; CI: 1.240 - 16.692, P = 0.025; respectively). The ESS early group had a significant reduction in the need for total antibiotic courses compared to the ESS delayed group (ESS early median: -1, IQR: -1.5 to -0.5 vs ESS delayed median: 0, IQR: 0 to 0; P = 0.027).

CONCLUSION

Earlier ESS interventions following lung transplantation may improve pulmonary function and attenuate pulmonary exacerbations in CF patients. This article is protected by copyright. All rights reserved.

Bacterial infections in lung transplantation

Lung transplantation has lower survival rates compared to other than other solid organ transplants (SOT) due to higher rates of infection and rejection-related complications, and bacterial infections (BI) are the most frequent infectious complications. Excess morbidity and mortality are not only a direct consequence of these BI, but so are subsequent loss of allograft tolerance, rejection, and chronic lung allograft dysfunction due to bronchiolitis obliterans syndrome (BOS). A wide variety of pathogens can cause infections in lung transplant recipients (LTRs), including a number of nosocomial pathogens and other multidrug-resistant (MDR) pathogens. Although pneumonia and intrathoracic infections predominate, LTRs are at risk of a number of types of infections. Risk factors include altered anatomy and function of airways, impaired immunity, the microbial flora of the donor and recipient, underlying medical conditions, and genetic factors. Further work on immune monitoring has the potential to improve outcomes. The infecting agents can be derived from the donor lung, pre-existing recipient flora, or acquired from the environment over time. Certain infections may preclude lung transplantation, but this varies from center to center, and more recent studies suggest fewer patients should be disqualified. New molecular methods allow microbiome studies of the lung, gut, and other sites that may further our knowledge of how airway colonization can result in infection and allograft loss. Surveillance, early diagnosis, and aggressive antimicrobial therapy of BI is critical in LTRs. Antibiotic resistance is a major barrier to successful management of these infections. The availability of new agents for MDR Gram-negatives may improve outcomes. Other new therapies, such as bacteriophage therapy, show promise for the future. Finally, it is important to prevent infections through peri-transplant prophylaxis, vaccination, and infection control measures.

Consensus document for the selection of lung transplant candidates: An update from the International Society for Heart and Lung Transplantation

Tens of thousands of patients with advanced lung diseases may be eligible to be considered as potential candidates for lung transplant around the world each year. The timing of referral, evaluation, determination of candidacy, and listing of candidates continues to pose challenges and even ethical dilemmas. To address these challenges, the International Society for Heart and Lung Transplantation appointed an international group of members to review the literature, to consider recent advances in the management of advanced lung diseases, and to update prior consensus documents on the selection of lung transplant candidates. The purpose of this updated consensus document is to assist providers throughout the world who are caring for patients with pulmonary disease to identify potential candidates for lung transplant, to optimize the timing of the referral of these patients to lung transplant centers, and to provide transplant centers with a framework for evaluating and selecting candidates. In addition to addressing general considerations and providing disease specific recommendations for referral and listing, this updated consensus document includes an ethical framework, a recognition of the variability in acceptance of risk between transplant centers, and establishes a system to account for how a combination of risk factors may be taken into consideration in candidate selection for lung transplantation.

Outcome and prognostic factors after lung transplantation for bronchiectasis other than cystic fibrosis

BACKGROUND

While lung transplant (LTX) can be an effective therapy to provide the survival benefit in selected populations, post-transplant outcome in LTX recipients with bronchiectasis other than cystic fibrosis (CF) has been less studied. Pseudomonas aeruginosa, often associated with exacerbations in bronchiectasis, is the most common micro-organism isolated from LTX recipients. We aimed to see the outcomes of patients with bronchiectasis other than CF after LTX and seek the risk factors associated with pre- and post-transplant Pseudomonas status.

METHODS

Patients who underwent LTX at Tohoku University Hospital between January 2000 and December 2020 were consecutively included into the retrospective cohort study. Pre- and post-transplant prevalence of Pseudomonas colonization between bronchiectasis and other diseases was reviewed. Post-transplant outcomes (mortality and the development of chronic lung allograft dysfunction (CLAD)) were assessed using a Cox proportional hazards and time-to-event outcomes were estimated using the Kaplan-Meier method.

RESULTS

LTX recipients with bronchiectasis experienced a high rate of pre- and post-transplant Pseudomonas colonization compared to other diseases with statistical significance (p < 0.001 and p < 0.001, respectively). Nevertheless, long-term survival in bronchiectasis was as great as non-bronchiectasis (Log-rank p = 0.522), and the bronchiectasis was not a trigger for death (HR 1.62, 95% CI 0.63-4.19). On the other hand, the chance of CLAD onset in bronchiectasis was comparable to non-bronchiectasis (Log-rank p = 0.221), and bronchiectasis was not a predictor of the development of CLAD (HR 1.88, 95% CI 0.65-5.40).

CONCLUSIONS

Despite high prevalence of pre- and post-transplant Pseudomonas colonization, the outcome in LTX recipients with bronchiectasis other than CF was comparable to those without bronchiectasis.

Cystic fibrosis foundation consensus statements for the care of cystic fibrosis lung transplant recipients

Cystic fibrosis (CF) is the indication for transplantation in approximately 15% of recipients worldwide, and Cystic Fibrosis Lung Transplant Recipients (CFLTRs) have excellent long-term outcomes. Yet, CFLTRs have unique comorbidities that require specialized care. The objective of this document is to provide recommendations to CF and lung transplant clinicians for the management of perioperative and underlying comorbidities of CFLTRs and the impact of transplantation on these comorbidities. The Cystic Fibrosis Foundation (CFF) organized a multidisciplinary committee to develop CF Lung Transplant Clinical Care Recommendations. Three workgroups were formed to develop focused questions. Following a literature search, consensus recommendations were developed by the committee members based on literature review, committee experience and iterative revisions, and in response to public comment. The committee formulated 32 recommendation statements in the topics related to infectious disease, endocrine, gastroenterology, pharmacology, mental health and family planning. Broadly, the committee recommends close coordination of care between the lung transplant team, the cystic fibrosis care center, and specialists in other disciplines with experience in the care of CF and lung transplant recipients. These consensus statements will help lung transplant providers care for CFLTRs in order to improve post-transplant outcomes in this population.

Bacterial Re-Colonization Occurs Early after Lung Transplantation in Cystic Fibrosis Patients

Most cystic fibrosis (CF) patients referred for lung transplantation are chronically infected with Gram-negative opportunistic pathogens. It is well known that chronic infections in CF patients have a significant impact on lung-function decline and survival before transplantation. The rate and timing of re-colonization after transplantation have been described, but the impact on survival after stratification of bacteria is not well elucidated. We did a single-center retrospective analysis of 99 consecutive CF patients who underwent lung transplantation since the beginning of the Copenhagen Lung Transplant program in 1992 until October 2014. Two patients were excluded due to re-transplantation. From the time of CF diagnosis, patients had monthly sputum cultures. After transplantation, CF-patients had bronchoscopy with bronchoalveolar lavage at 2, 4, 6 and 12 weeks and 6, 12, 18 and 24 months after transplantation, as well as sputum samples if relevant. Selected culture results prior to and after transplantation were stored. We focused on colonization with the most frequent bacteria: Pseudomonas aeruginosa (PA), Stenotrophomonas maltophilia (SM), Achromobacter xylosoxidans (AX) and Burkholderia cepacia complex (BCC). Pulsed-field gel electrophoresis (PFGE) was used to identify clonality of bacterial isolates obtained before and after lung transplantation. Time to re-colonization was defined as the time from transplantation to the first positive culture with the same species. Seventy-three out of 97 (75%) had sufficient culture data for analyses with a median of 7 (1–91) cultures available before and after transplantation. Median colonization-free survival time was 23 days until the first positive culture after transplantation. After 2 years, 59 patients (81%) were re-colonized, 33 (48.5%) with PA, 7 (10.3%) with SM, 12 (17.6%) with AX, and 7 (10.3%) with BCC. No difference in survival was observed between the patients colonized within the first 2 years and those not colonized. Re-colonization of bacteria in the lower airways occurred at a median of 23 days after transplantation in our cohort. In our patient cohort, survival was not influenced by re-colonization or bacterial species.

International consensus statement on allergy and rhinology: rhinosinusitis 2021

I.

EXECUTIVE SUMMARY

BACKGROUND: The 5 years since the publication of the first International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICAR-RS) has witnessed foundational progress in our understanding and treatment of rhinologic disease. These advances are reflected within the more than 40 new topics covered within the ICAR-RS-2021 as well as updates to the original 140 topics. This executive summary consolidates the evidence-based findings of the document.

METHODS

ICAR-RS presents over 180 topics in the forms of evidence-based reviews with recommendations (EBRRs), evidence-based reviews, and literature reviews. The highest grade structured recommendations of the EBRR sections are summarized in this executive summary.

RESULTS

ICAR-RS-2021 covers 22 topics regarding the medical management of RS, which are grade A/B and are presented in the executive summary. Additionally, 4 topics regarding the surgical management of RS are grade A/B and are presented in the executive summary. Finally, a comprehensive evidence-based management algorithm is provided.

CONCLUSION

This ICAR-RS-2021 executive summary provides a compilation of the evidence-based recommendations for medical and surgical treatment of the most common forms of RS.

Challenges in the use of highly effective modulator treatment for cystic fibrosis

The last decade has seen development of oral, small molecule therapies that address the basic cystic fibrosis transmembrane conductance regulator (CFTR) protein defect. Highly effective modulator treatment (HEMT) that is efficacious for a large majority of people living with cystic fibrosis (CF) promises to change the landscape of this chronic life-limiting disease. Some people living with CF have a CFTR genotype that renders them eligible for HEMT, but also have comorbidities that excluded them from the original Phase III clinical trials that led to US Food and Drug Administration approval. The purpose of this review is to address the use of HEMT in challenging situations, including initiation for those with advanced CF lung disease, and use after solid organ transplant, during pregnancy, and for individuals with CFTR-related disorders without a definitive diagnosis of CF.

Chronic rhinosinusitis in patients with cystic fibrosis-Current management and new treatments

OBJECTIVES

The purpose of this article is to provide a state-of-the-art review of the literature and summarize the latest publications on medical and surgical treatment of cystic fibrosis (CF) chronic rhinosinusitis (CRS), with an emphasis on describing recent advancements in cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies.

METHODS

A comprehensive literature review was conducted utilizing the PubMed database with search phrases detailed within the body of the article. Abstracts were reviewed to include publications detailing medical, surgical, and CFTR modulating therapies for CF CRS. Findings from studies not previously reviewed and publications regarding CFTR modulators were emphasized.

RESULTS

No clear guidelines for treatment of CF CRS are available. Nasal saline rinses, topical steroids, topical antibiotics, and topical dornase alfa are reported medical therapies. Ivacaftor has some sinonasal symptomatic benefit. A new triple therapy CFTR modulator, elexacaftor/tezacaftor/ivacaftor, is capable of treating 90% of patients with CF and has shown the greatest FEV1 improvement of any CFTR modulator yet. There is no clear consensus on surgical indications or technique, though aggressive surgery in recalcitrant disease has shown some symptomatic benefit. Endoscopic sinus surgery after lung transplantation may benefit some patients in whom the sinuses serve as a reservoir for recurrent pulmonary infections by decreasing rates of bronchiolitis obliterans syndrome and improving 5 year survival.

CONCLUSION

As lifespan increases for patients with CF, further investigation into medical therapy, CFTR modulator sinonasal outcomes, and surgical technique and outcomes for CF CRS is needed.

LEVEL OF EVIDENCE

5.

Multidrug-resistant Gram-negative bacterial infections in solid organ transplant recipients-Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the Infectious Diseases Community of Practice of the American Society of Transplantation review the diagnosis, prevention, and management of infections due to multidrug-resistant (MDR) Gram-negative bacilli in the pre- and post-transplant period. MDR Gram-negative bacilli, including carbapenem-resistant Enterobacteriaceae, MDR Pseudomonas aeruginosa, and carbapenem-resistant Acinetobacter baumannii, remain a threat to successful organ transplantation. Clinicians now have access to at least five novel agents with activity against some of these organisms, with others in the advanced stages of clinical development. No agent, however, provides universal and predictable activity against any of these pathogens, and very little is available to treat infections with MDR nonfermenting Gram-negative bacilli including A baumannii. Despite advances, empiric antibiotics should be tailored to local microbiology and targeted regimens should be tailored to susceptibilities. Source control remains an important part of the therapeutic armamentarium. Morbidity and mortality associated with infections due to MDR Gram-negative organisms remain unacceptably high. Heightened infection control and antimicrobial stewardship initiatives are needed to prevent these infections, curtail their transmission, and limit the evolution of MDR Gram-negative pathogens, especially in the setting of organ transplantation.

Surgical Management of Chronic Rhinosinusitis in Cystic Fibrosis

Cystic fibrosis patients frequently develop chronic rhinosinusitis as a result of their propensity to form inspissated mucus and impairment of mucociliary clearance. They exhibit variable symptom burden even in the setting of positive radiographic and endoscopic findings. Current evidence suggests a positive effect of managing sinonasal disease on pulmonary health. Topical antimicrobial and mucolytic therapies are frequently required to manage the disease with surgery reserved for refractory cases. Endoscopic sinus surgery has been demonstrated to be safe and efficacious in controlling symptoms of chronic rhinosinusitis in patients with comorbid cystic fibrosis. However, the impact of surgery on pulmonary health remains an active area of investigation. In addition, a growing body of research has suggested a more extended surgical approach creating large sinonasal cavities with gravity-dependent drainage pathways, followed by adjuvant medical therapies, as an ideal strategy to optimally control disease and prevent pulmonary exacerbations. In this manuscript, we provide an up-to-date review of current evidence in the surgical management of chronic rhinosinusitis in cystic fibrosis patients.

Outcomes of endoscopic sinus surgery in adult lung transplant patients with cystic fibrosis

PURPOSE

Cystic Fibrosis (CF) is the most common autosomal recessive disease in Caucasian population. Due to its pathological mechanism, chronic rhino sinusitis (CRS) associated or not with nasal polyposis usually occurs in adults and affects close to one-half of all CF patients. The goal of our work was to evaluate the impact of Endoscopic Sinus Surgery (ESS) in the quality of life (QoL) of the CF patients and demonstrate an improvement of the functional outcomes in the patients underwent the surgical procedure rather than in the not treated ones, particulary in lung transplant patients.

METHODS

We studied 54 adult patients affected by CF. Lund-Kennedy, Lund-Mackay scores, and SNOT-22 were analysed. 14 had lung transplant and 9 had both lung tranplant and ESS procedures.

RESULTS

22 (40.7%) out of 54 CF patients underwent ESS. This group presented more likely complaints consistent with CRS. Lund-Kennedy and Lund-Mackay scores appeared higher in the ESS group: 10 (range of 6-12) and 15 (range of 12-20), respectively. SNOT-22 showed median values for non-ESS and ESS group of 20 (range of 3-68) and 40 (range of 10-73), respectively.

CONCLUSIONS

ESS represents the best option to improve clinical QoL of CF patients who do not response to conventional medical therapy, with a stabilization of respiratory function after transplantation.

Loss of Microbial Niche Specificity Between the Upper and Lower Airways in Patients With Cystic Fibrosis

OBJECTIVES/HYPOTHESIS

To determine the relationship between mucosal-associated sinus and bronchial microbiota in cystic fibrosis (CF) patients compared to non-CF patients with chronic rhinosinusitis (CRS).

STUDY DESIGN

Case series.

METHODS

We examined the microbial composition of 52 paired sinus and bronchial brushings from 26 patients with CRS. Paired airway samples from nine subjects with CF were compared with samples from 17 non-CF-CRS disease control patients. The Illumina MiSeq platform was used to sequence the V4 region of the 16S rRNA gene. Sequences were analyzed using QIIME 1.9.0.

RESULTS

CF patients demonstrate increased severity of sinus inflammation (Lund-Mackay score 16.3 vs. 12.4, P = .023) and diminished diversity of microbial communities in both the sinuses (Shannon diversity 0.98 vs. 3.3, P = .009) and lungs (Shannon diversity 2.2 vs. 4.0, P = .042) relative to non-CF-CRS. Non-CF-CRS sinus and lung microbiota were distinct and clustered by niche (sinus vs. lung, P = .004). However, CF airway microbiota demonstrated a loss of niche specificity (sinus vs. lung, P = .492). Two CF patients underwent lung transplantation at 4.5 and 9 months prior to sampling. Sinus and lung samples from these two patients demonstrated distinct microbial communities.

CONCLUSIONS

Patients with CF undergoing surgery for CRS exhibit substantial bacterial community collapse in the sinuses and a loss of niche specificity between the upper and lower airways compared to non-CF patients with CRS. These results extend previous studies elucidating the lower airway microbiome in cystic fibrosis and provide support for the concept of microbial translocation in the cystic fibrosis airways.

LEVEL OF EVIDENCE

4 Laryngoscope, 129:544-550, 2019.

Risks associated with lung transplantation in cystic fibrosis patients

INTRODUCTION

Survival after lung transplantation lags behind outcomes of other solid organ transplants, and complications from lung transplant are the second most common cause of death in cystic fibrosis. Evolving surgical techniques, therapeutics, and perioperative management have improved short-term survival after lung transplantation, yet have not translated into significant improvement in long-term mortality. Areas covered: We review risk factors for poor long-term outcomes among patients with cystic fibrosis undergoing lung transplantation to highlight areas for improvement. This includes reasons for organ dysfunction, complications of immunosuppression, further exacerbation of extrapulmonary complications of cystic fibrosis, and quality of life. A literature search was performed using PubMed-indexed journals. Expert commentary: There are multiple medical and socioeconomic barriers that threaten long-term survival following lung transplant for patients with cystic fibrosis. An understanding of the causes of each could elucidate treatment options. There is a lack of prospective, multicenter, randomized control trials due to cost, complexity, and feasibility. Ongoing prospective studies should be reserved for the most promising interventions identified in retrospective studies in order to improve long-term outcomes.

Sinus bacteriology in patients with cystic fibrosis or primary ciliary dyskinesia: A systematic review

BACKGROUND

A correlation exists between the microbial flora of the upper and lower airways in patients with cystic fibrosis (CF) or with primary ciliary dyskinesia (PCD). The sinuses can function as a bacterial reservoir where gram-negative bacteria adapt to the airways and repeatedly are aspirated to and colonize the lungs according to the theory of the united (unified) airways. Whereas the pattern of bacterial flora in the lower airways has been extensively studied, the upper airways have drawn limited attention.

OBJECTIVE

Our aim was to review the literature that reported bacterial flora in the sinuses and nasal cavities of patients with CF or PCD.

METHODS

A number of medical literature data bases were systematically searched between January 1960 and July 2016. We applied the following inclusion criteria: a minimum of one case of PCD (or Kartagener syndrome) or CF, and microbiology analyses from the nose or paranasal sinuses.

RESULTS

We included 46 studies (1823 patients) from 16 countries. Staphylococcus aureus was found in 30% of the noses and sinuses of patients with CF. Other common bacteria found included Pseudomonas aeruginosa, coagulase negative staphylococci, and Haemophilus influenzae. In PCD, H. influenzae was the most common bacteria (28%), followed by Streptococcus pneumoniae and P. aeruginosa. If studies that included nonsurgical swab and blowing samples were excluded, then P. aeruginosa was the most common bacterium in patients with CF (34%) and in patients with PCD (50%), followed by S. aureus and H. influenza.

CONCLUSION

S. aureus, P. aeruginosa, coagulase negative staphylococci, and H. influenzae dominated in the upper airways of patients with CF. In patients with PCD, H. influenzae, S. pneumoniae, and P. aeruginosa dominated. When studies that included swab and blowing samples were excluded, P. aeruginosa was the most common bacterium in both groups. Direct comparisons among the studies were restricted due to very heterogeneous methods, and a better standardization of procedures and outcomes is needed.

Correlation between sinus and lung cultures in lung transplant patients with cystic fibrosis

BACKGROUND

Lung transplantation has revolutionized the treatment of end-stage pulmonary disease due to cystic fibrosis. However, infection of the transplanted lungs can lead to serious complications, including graft failure and death. Although many of these patients have concurrent sinusitis, it is unclear whether bacteria from the sinuses can infect the allograft.

METHODS

This is a single-institution retrospective study of all patients who underwent lung transplantation for cystic fibrosis from 2005 to 2015 at Duke University Hospital. Pre- and posttransplant nasal and pulmonary cultures obtained via nasal endoscopy and bronchoalveolar lavage (BAL), respectively, were analyzed.

RESULTS

A total of 141 patients underwent 144 lung transplants. Sinus cultures were available for 76 patients (12 pretransplant, 42 posttransplant, 22 both pre- and posttransplant). Pretransplant BAL cultures were available for 139 patients, and posttransplant BAL cultures were available for all patients. Pseudomonas aeruginosa (PsA) and methicillin-resistant Staphylococcus aureus (MRSA) were the most common organisms cultured. There was a significant correlation between pretransplant sinus and posttransplant BAL cultures for PsA (p = 0.003), MRSA (p = 0.013), and Burkholderia cepacia (p = 0.001).

CONCLUSION

There was a high correlation between pretransplant sinus cultures and posttransplant BAL cultures for PsA, MRSA, and Burkholderia sp. This suggests that the paranasal sinuses may act as a reservoir for allograft colonization in patients with cystic fibrosis. Further studies are needed to determine whether treatment of sinusitis affects allograft colonization and transplant outcomes.

Prevention of chronic rejection after lung transplantation

Long-term survival after lung transplantation (LTx) is limited by chronic rejection (CR). Therapeutic strategies for CR have been largely unsuccessful, making prevention of CR an important and challenging therapeutic approach. In the current review, we will discuss current clinical evidence regarding prevention of CR after LTx.

Assessment of Pulmonary Function before and after Sinus Surgery in Lung Transplant Recipients

Introduction  The association between sinus and lung diseases is well known. However, there are scarce studies regarding the effects of sinus surgery on pulmonary function in lung transplant recipients. The present study describes our experience with sinus surgery in lung transplant recipients with chronic rhinosinusitis. Objectives  To assess the impact of sinus surgery for chronic rhinosinusitis on pulmonary function and on inpatient hospitalization days due to lower respiratory tract infection in lung transplant recipients. Methods  A retrospective study conducted between 2006 and 2012 on a sample of lung transplant recipients undergoing sinus surgery for chronic rhinosinusitis. Pulmonary function, measured by forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1), as well as inpatient hospitalization days due to lower respiratory tract infection, were compared 6 months before and 6 months after sinus surgery. Results  The FEV1 values increased significantly, and the inpatient hospitalization days due to bronchopneumonia decreased significantly 6 months after sinus surgery. The preoperative and postoperative median FEV1 values were 2.35 and 2.68 respectively ( p  =  0.0056 ). The median number of inpatient hospitalization days due to bronchopneumonia 6 months before and 6 months after surgery were 32.82 and 5.41 respectively ( p  =  0.0013 ). Conclusion  In this sample of lung transplant recipients with chronic rhinosinusitis, sinus surgery led to an improvement in pulmonary function and a decrease in inpatient hospitalization days due to bronchopneumonia.

Tracheal diverticula in advanced cystic fibrosis: Prevalence, features, and outcomes after lung transplantation

BACKGROUND

Tracheal diverticula (TD) are rare anomalies that may harbor infected secretions, posing potential risk to patients with lung disease. In an end-stage cystic fibrosis (CF) cohort, we describe the characteristics and associated post-lung transplant (LTx) outcomes of TD.

METHODS

Pre-transplant computed tomography (CT)'s were reviewed in CF patients undergoing LTx. TD were characterized radiographically and on autopsy when available. Pre-transplant clinical variables and post-transplant outcomes were compared by TD status.

RESULTS

Of 93 patients, 35 (37.6%) had TD. 58% of TD had fat-stranding, and post-mortem TD examinations revealed histology carrying intense submucosal inflammation, and purulent contents that cultured identical species to sputum. There was no difference in post-LTx survival [HR 1.77 (0.82-3.82), p=0.147], bacterial re-colonization, or rejection in patients with TD compared to those without. Patients with TD were more likely to die from infection, but the result was not statistically significant [HR 2.02 (0.62-6.63), p=0.245].

CONCLUSIONS

We found a high prevalence of TD in end-stage CF, where diverticula may represent a large-airway bacterial reservoir. TD were not associated with differences in post-LTx outcomes, but given the infectious concerns further investigation is necessary.

The treatment of the pulmonary and extrapulmonary manifestations of cystic fibrosis

Cystic fibrosis (CF) is a complex multisystem disease with considerable between patient variability in its manifestations and severity. In the past several decades, the range of treatments and the evidence to support their use for the pulmonary and extrapulmonary manifestations of CF have increased dramatically, contributing to the improved median survival of patients. As therapy for CF has evolved, new challenges including treatment adherence, medication intolerance and allergy, medical complications and coping with the burden of disease in the context of having a family and managing employment have arisen. While the majority of current therapy focuses primarily on improving symptoms, new therapies (CFTR modulators) target the underlying genetic defect.

The impact of chronic rhinosinusitis on long-term survival in lung transplantation recipients

CONCLUSIONS

Chronic rhinosinusitis diagnosed according to the European Position Paper on Rhinosinusitis and Nasal Polyps 2012, not by computed tomography alone, is one of the prognostic factors affecting long-term survival in patients with lung transplantation. Endoscopic sinus surgery might play a beneficial role in the management of lung transplantation recipients with chronic rhinosinusitis.

OBJECTIVE

To show the effect of paranasal sinus infection on post-lung transplantation survival.

METHOD

Lung transplantation recipients were included in this study. Computed tomography was performed before and after lung transplantation. The severity of chronic rhinosinusitis was evaluated by Lund-Mackay scoring system. The survival rate was calculated by the Kaplan-Meier method.

RESULTS

One hundred and forty-eight patients received lung transplantation for various indications. Chronic rhinosinusitis was found in 18.9% (28/148) of the lung transplantation recipients. Of 28 patients with chronic rhinosinusitis, seven patients underwent endoscopic sinus surgery due to persistent post-nasal drip. The recipients with chronic rhinosinusitis who did not receive endoscopic sinus surgery (n = 21) showed a significantly lower survival rate as compared to the patients without chronic rhinosinusitis. There was no statistically significant difference in the survival rate between the recipients with (n = 50) and without (n = 98) paranasal sinus abnormality on computed tomography.

Systemic and Odontogenic Etiologies in Chronic Rhinosinusitis

Systemic and odontogenic etiologies of chronic rhinosinusitis, although rare, are an integral consideration in the comprehensive management of patients with sinonasal disease. Proper knowledge and timely recognition of each disease process, with referrals to appropriate consultants, will facilitate treatment, because many of these conditions require both local and systemic therapy. In some instances, medical therapy plays a pivotal role, with surgery being a supplemental treatment technique. We review the most commonly encountered systemic etiologies of chronic rhinosinusitis and odontogenic sinusitis, including clinical presentation, diagnosis, management, and treatment outcomes.

Microbial Communities of Conducting and Respiratory Zones of Lung-Transplanted Patients

Background: Lung transplantation (LT) is a recognized treatment for end-stage pulmonary disease. Bacteria from the recipient nasopharynx seed the new lungs leading to infections and allograft damage. Understanding the characteristics and topological variations of the microbiota may be important to apprehend the pathophysiology of allograft dysfunction.

Objectives: To examine the characteristics and relationship of bacterial compositions between conducting and respiratory zones of the allograft.

Methods: We performed 16S rRNA gene sequencing on bronchial aspirates (BAs) and bronchoalveolar lavages (BALs) collected in pairs in 19 patients at several time-points post-LT.

Results: The respiratory zone was characterized independently of the time post-LT by a higher bacterial richness than the conducting zone (p = 0.041). The phyla Firmicutes and Proteobacteria dominated both sampling zones, with an inverse correlation between these two phyla (Spearman r = –0.830). Samples of the same pair, as well as pairs from the same individual clustered together (Pseudo-F = 3.8652, p < 0.01). Microbiota of BA and BAL were more closely related in samples from the same patient than each sample type across different patients, with variation in community structure being mainly inter-individual (p < 0.01). Both number of antibiotics administered (p < 0.01) and time interval post-LT (p < 0.01) contributed to the variation in global microbiota structure. Longitudinal analysis of BA–BAL pairs of two patients showed dynamic wave like fluctuations of the microbiota.

Conclusions: Our results show that post-transplant respiratory zones harbor higher bacterial richness, but overall similar bacterial profiles as compared to conductive zones. They further support an individual microbial signature following LT.

Transplantation

Despite improvement in median life expectancy and overall health, some children with cystic fibrosis (CF) progress to end-stage lung or liver disease and become candidates for transplant. Transplants for children with CF hold the promise to extend and improve the quality of life, but barriers to successful long-term outcomes include shortage of suitable donor organs; potential complications from the surgical procedure and immunosuppressants; risk of rejection and infection; and the need for lifelong, strict adherence to a complex medical regimen. This article reviews the indications and complications of lung and liver transplantation in children with CF.

Comprehensive review on endonasal endoscopic sinus surgery

Endonasal endoscopic sinus surgery is the standard procedure for surgery of most paranasal sinus diseases. Appropriate frame conditions provided, the respective procedures are safe and successful. These prerequisites encompass appropriate technical equipment, anatomical oriented surgical technique, proper patient selection, and individually adapted extent of surgery. The range of endonasal sinus operations has dramatically increased during the last 20 years and reaches from partial uncinectomy to pansinus surgery with extended surgery of the frontal (Draf type III), maxillary (grade 3-4, medial maxillectomy, prelacrimal approach) and sphenoid sinus. In addition there are operations outside and beyond the paranasal sinuses. The development of surgical technique is still constantly evolving. This article gives a comprehensive review on the most recent state of the art in endoscopic sinus surgery according to the literature with the following aspects: principles and fundamentals, surgical techniques, indications, outcome, postoperative care, nasal packing and stents, technical equipment.

Bacterial sinusitis can be a focus for initial lung colonisation and chronic lung infection in patients with cystic fibrosis

A major purpose of treating patients with cystic fibrosis (CF) is to prevent or delay chronic lung infections with CF-pathogenic Gram-negative bacteria. In the intermittent stage, bacteria can usually be eradicated from the lungs with antibiotics, but following eradication, the next lung colonisations often occur with bacteria of identical genotype. This may be due to re-colonisation from the patient's paranasal sinuses. In our study, we found that approximately two-thirds of CF patients having sinus surgery (FESS) had growth of CF-lung-pathogenic Gram-negative bacteria in their sinuses (Pseudomonas aeruginosa, Achromobacter xylosoxidans, Burkholderia cepacia complex). The environment in the sinuses is in many ways similar to that of the lower respiratory tract, e.g. low oxygen concentration in secretions. Sinus bacteria are more difficult to eradicate than in the lungs, thus, having good conditions for adapting to the environment in the lungs. In the presence of bacteria, the environment of the sinuses differs from that of the lower respiratory tract by having a higher immunoglobulin A (IgA): IgG ratio, and reduced inflammation. We found a significant correlation between the concentration of IgA against P. aeruginosa (standard antigen and alginate) in nasal secretions and saliva and CF patients' infection status (not lung colonised, intermittently colonised or chronically lung-infected with P. aeruginosa). This supports the hypothesis that infections often originate in the sinuses and can be a focus for initial lung colonisation or for maintaining lung infections in CF patients. We are confident that anti-P. aeruginosa IgA can be used as an early supplementary tool to diagnose P. aeruginosa colonisation; P. aeruginosa being the microorganism causing most morbidity and mortality in CF patients. This is important since urgent treatment reduces morbidity when CF patients are early colonised with P. aeruginosa, however, there is a lack of diagnostic tools for detecting the early colonisation in the lungs and in the sinuses. We initiated a treatment strategy for CF patients to prevent sino-nasal bacteria being seeded into the lower airways: we recommended extensive functional endoscopic FESS with creation of sufficient drainage from all involved sinuses with subsequent i.v. antibiotics and at least 6 months of twice daily nasal irrigation with saline and antibiotics. By this strategy, sinus bacteria could be eradicated in a large proportion of patients. Essentially, growth of CF-pathogenic bacteria from the lower respiratory tract was decreased following the treatment. Furthermore, a number of patients have been free from CF-pathogenic bacteria for more than one year after FESS, and thus re-classified as "not lung colonised". We also corroborated that CF patients obtain an improved quality of life and reduction in their symptoms of chronic rhinosinusitis after FESS. It is primarily intermittently lung colonised CF patients with CF-pathogenic bacteria in their sinuses that seem to benefit from the treatment strategy. This is in accordance with the fact that we did not see a significant increase in lung function and only a small decrease in specific antibodies after FESS; a high systemic immune and inflammatory response and a decreasing lung function is generally not present in patients who primarily have sinus CF-pathogenic bacteria. It is important that guidelines are created for how CF patients with CF-pathogenic bacteria in the sinuses are to be treated, including criteria for who may likely benefit from FESS, and who may be treated exclusively with conservative therapy, e.g. saline and antibiotic irrigations.

Paranasal sinus pathogens in children with cystic fibrosis: do they relate to lower respiratory tract pathogens and is eradication successful?

BACKGROUND

The study aims were to assess the association of microflora between the paranasal sinus and the lower airways of children attending a regional paediatric cystic fibrosis centre and to determine the performance of an eradication treatment protocol for positive paranasal sinus samples.

METHOD

Paired nasal lavage and lower airway samples (cough swabs or sputum) were taken from 54 children with cystic fibrosis (median age 11 years). Positive paranasal sinus samples received eradication treatment, using oral and sinonasal nebulised antibiotics.

RESULTS

A correlation between paranasal sinus and lower airways was detected in 33/54 paired timed samples (p<0.02). Of 4/54 children who reported sinus symptoms, only 2 had paranasal sinus positive samples. 28 positive nasal lavage samples cultured 8 Pseudomonas aeruginosa (PA), 8 Staphylococcus aureus (SA) and 12 other bacterial pathogens. Eradication using sinonasal nebulised antibiotics and oral antibiotics showed a success of 14/21 (67%) treated paranasal sinus positive samples at 1 month & 3 months after treatment. Success rate was 75% in the PA group and 71% in the SA group. Ongoing monitoring with nasal lavage will continue.

CONCLUSION

There was agreement between pathogens or lack of them found in the paranasal sinus and lower airways. Paranasal infection is often asymptomatic in children with cystic fibrosis. The eradication protocol for paranasal sinus pathogens had a good success rate.

Practical guidelines: lung transplantation in patients with cystic fibrosis

There are no European recommendations on issues specifically related to lung transplantation (LTX) in cystic fibrosis (CF). The main goal of this paper is to provide CF care team members with clinically relevant CF-specific information on all aspects of LTX, highlighting areas of consensus and controversy throughout Europe. Bilateral lung transplantation has been shown to be an important therapeutic option for end-stage CF pulmonary disease. Transplant function and patient survival after transplantation are better than in most other indications for this procedure. Attention though has to be paid to pretransplant morbidity, time for referral, evaluation, indication, and contraindication in children and in adults. This review makes extensive use of specific evidence in the field of lung transplantation in CF patients and addresses all issues of practical importance. The requirements of pre-, peri-, and postoperative management are discussed in detail including bridging to transplant and postoperative complications, immune suppression, chronic allograft dysfunction, infection, and malignancies being the most important. Among the contributors to this guiding information are 19 members of the ECORN-CF project and other experts. The document is endorsed by the European Cystic Fibrosis Society and sponsored by the Christiane Herzog Foundation.

Comorbidities impacting on prognosis after lung transplant

The aim of this review is to give an overview of the clinical circumstances presenting before lung transplant that may have negative repercussions on the long and short-term prognosis of the transplant. Methods for screening and diagnosis of common comorbidities with negative impact on the prognosis of the transplant are proposed, both for pulmonary and extrapulmonary diseases, and measures aimed at correcting these factors are discussed. Coordination and information exchange between referral centers and transplant centers would allow these comorbidities to be detected and corrected, with the aim of minimizing the risks and improving the life expectancy of transplant receivers.

Respiratory infections in patients with cystic fibrosis undergoing lung transplantation

Cystic fibrosis is an inherited disease characterised by chronic respiratory infections associated with bronchiectasis. Lung transplantation has helped to extend the lives of patients with cystic fibrosis who have advanced lung disease. However, persistent, recurrent, and newly acquired infections can be problematic. Classic cystic fibrosis-associated organisms, such as Staphylococcus aureus and Pseudomonas aeruginosa, are generally manageable post-transplantation, and are associated with favourable outcomes. Burkholderia cenocepacia poses particular challenges, although other Burkholderia species are less problematic. Despite concerns about non-tuberculous mycobacteria, especially Mycobacterium abscessus, post-transplantation survival has not been definitively shown to be less than average in patients with these infections. Fungal species can be prevalent before and after transplantation and are associated with high morbidity, so should be treated aggressively. Appropriate viral screening and antiviral prophylaxis are necessary to prevent infection with and reactivation of Epstein-Barr virus and cytomegalovirus and their associated complications. Awareness of drug pharmacokinetics and interactions in cystic fibrosis is crucial to prevent toxic effects and subtherapeutic or supratherapeutic drug dosing. With the large range of potential infectious organisms in patients with cystic fibrosis, infection control in hospital and outpatient settings is important. Despite its complexity, lung transplantation in the cystic fibrosis population is safe, with good outcomes if the clinician is aware of all the potential pathogens and remains vigilant by means of surveillance and proactive treatment.

The effect of sinus surgery with intensive follow-up on pathogenic sinus bacteria in patients with cystic fibrosis

BACKGROUND

Most patients with cystic fibrosis (CF) have chronic rhinosinusitis; their sinuses are often colonized with bacteria that can initiate and maintain deleterious pulmonary infections. Theoretically, eradication of the sinus bacteria should reduce the frequency of lung infections and thereby reduce pulmonary morbidity. This article addressed whether bacteria in CF sinuses are eligible for eradication by sinus surgery and postoperative treatment.

METHODS

A prospective study including 58 CF patients, who had extensive sinus surgery and growth of Pseudomonas aeruginosa, Achromobacter xylosoxidans, and/or Burkholderia multivorans in their sinuses, was initiated. All patients followed a systematic postoperative treatment program of nasal irrigations with saline and colistimethate sodium and systematic endoscopic cleansing. All patients had follow-up examinations including sinus cultures; each side of the nose was cultured separately.

RESULTS

At the 6-month follow-up visit, 49 patients were cultured; 66 of 98 maxillary-ethmoidal complexes (67%) showed no growth of pathogenic bacteria. Some patients were not free from CF pathogenic bacteria at all cultures; however, 20 (41%) patients had no bilateral regrowth (p < 0.01) and 4 patients had no unilateral regrowth at any time during 6 months of follow-up. The eradication of CF pathogens was accomplished in patients from all three lung infection groups: intermittently colonized, chronically infected, and lung transplanted. The patient with the longest follow-up had no bacterial growth for 3 years.

CONCLUSION

Extensive sinus surgery combined with intensive follow-up can eradicate pathogenic bacteria from CF sinuses.

P. aeruginosa in the paranasal sinuses and transplanted lungs have similar adaptive mutations as isolates from chronically infected CF lungs

BACKGROUND

Pseudomonas aeruginosa cells are present as biofilms in the paranasal sinuses and the lungs of chronically infected cystic fibrosis (CF) patients. Since different inflammatory responses and selective antibiotic pressures are acting in the sinuses compared with the lungs, we compared the adaptive profiles of mucoid and non-mucoid isolates from the two locations.

METHODS

We studied the genetic basis of phenotypic diversification and gene expression profiles in sequential lung and sinus P. aeruginosa isolates from four chronically infected CF patients, including pre- and post-lung transplantation isolates.

RESULTS

The same phenotypes caused by similar mutations and similar gene expression profiles were found in mucoid and non-mucoid isolates from the paranasal sinuses and from the lungs before and after transplantation.

CONCLUSION

Bilateral exchange of P. aeruginosa isolates between the paranasal sinuses and the lungs occurs in chronically infected patients and extensive sinus surgery before the lung transplantation might prevent infection of the new lung.

Reestablishment of recipient-associated microbiota in the lung allograft is linked to reduced risk of bronchiolitis obliterans syndrome

RATIONALE

Bronchiolitis obliterans syndrome (BOS) is the primary limiting factor for long-term survival after lung transplantation, and has previously been associated with microbial infections.

OBJECTIVES

To cross-sectionally and longitudinally characterize microbial communities in allografts from transplant recipients with and without BOS using a culture-independent method based on high-throughput sequencing.

METHODS

Allografts were sampled by bronchoalveolar lavage, and microbial communities were profiled using 16S rRNA gene amplicon pyrosequencing. Community profiles were compared using the weighted Unifrac metric and the relationship between microbial populations, BOS, and other covariates was explored using PERMANOVA and logistic regression.

MEASUREMENTS AND MAIN RESULTS

Microbial communities in transplant patients fell into two main groups: those dominated by Pseudomonas or those dominated by Streptococcus and Veillonella, which seem to be mutually exclusive lung microbiomes. Aspergillus culture was also negatively correlated with the Pseudomonas-dominated group. The reestablishment of dominant populations present in patients pretransplant, notably Pseudomonas in individuals with cystic fibrosis, was negatively correlated with BOS.

CONCLUSIONS

Recolonization of the allograft by Pseudomonas in individuals with cystic fibrosis is not associated with BOS. In general, reestablishment of pretransplant lung populations in the allograft seems to have a protective effect against BOS, whereas de novo acquisition of microbial populations often belonging to the same genera may increase the risk of BOS.