Environment or host?: A case-control study of risk factors for Mycobacterium avium complex lung disease

Treatable traits and challenges in the clinical management of non-tuberculous mycobacteria lung disease in people with cystic fibrosis

INTRODUCTION

Over the last ten years an increasing prevalence and incidence of non-tuberculous mycobacteria (NTM) has been reported among patients with cystic fibrosis (CF) Viviani (J Cyst Fibros, 15(5):619-623, 2016). NTM pulmonary disease has been associated with negative clinical outcomes and often requires pharmacological treatment. Although specific guidelines help clinicians in the process of diagnosis and clinical management, the focus on the multidimensional assessment of concomitant problems is still scarce.

MAIN BODY

This review aims to identify the treatable traits of NTM pulmonary disease in people with CF and discuss the importance of a multidisciplinary approach in order to detect and manage all the clinical and behavioral aspects of the disease. The multidisciplinary complexity of NTM pulmonary disease in CF requires careful management of respiratory and extra-respiratory, including control of comorbidities, drug interactions and behavioral factors as adherence to therapies.

CONCLUSIONS

The treatable trait strategy can help to optimize clinical management through systematic assessment of all the aspects of the disease, providing a holistic treatment for such a multi-systemic and complex condition.

Nontuberculous Mycobacterial Pulmonary Disease in the Immunocompromised Host

The immunocompromised host is at an increased risk for pulmonary and extrapulmonary NTM infections. Where data are available in these specific populations, increased mortality is observed with NTM disease. Prior to starting therapy for NTM disease, providers should ensure diagnostic criteria are met as treatment is long and often associated with significant side effects and toxicities. Treatment should involve 2 to 4 agents and be guided by cultures and antimicrobial susceptibilities. Drug interactions are important to consider, especially in those with HIV or transplant recipients. Whenever possible, immunosuppression should be reduced or changed.

Global Epidemiology of Nontuberculous Mycobacterial Pulmonary Disease: A Review

Nontuberculous mycobacterial (NTM) isolation and pulmonary disease (NTM-PD) have continued to increase in most regions of the world, driven mainly by Mycobacterium avium. Single-center studies also support increasing trends as well as a persistent burden of undiagnosed NTM among persons suspected of having tuberculosis (TB), in countries with moderate-to-high TB prevalence. Cumulative exposure to water and soil presents an increased risk to susceptible hosts, and trace metals in water supply are recently recognized risk factors. Establishing standard case definitions for subnational and national surveillance systems with mandatory notification of NTM-PD are needed to allow comparisons within and across countries and regions.

Towards development of evidence to inform recommendations for the evaluation and management of bronchiectasis

Bronchiectasis (BE) is a chronic condition characterized by airway dilation as a consequence of a variety of pathogenic processes. It is often associated with persistent airway infection and an inflammatory response resulting in cough productive of purulent sputum, which has an adverse impact on quality of life. The prevalence of BE is increasing worldwide. Treatment guidelines exist for managing BE, but they are generally informed by a paucity of high-quality evidence. This review presents the findings of a scientific advisory board of experts held in the United States in November 2020. The main focus of the meeting was to identify unmet needs in BE and propose ways to identify research priorities for the management of BE, with a view to developing evidence-based treatment recommendations. Key issues identified include diagnosis, patient evaluation, promoting airway clearance and appropriate use of antimicrobials. Unmet needs include effective pharmacological agents to promote airway clearance and reduce inflammation, control of chronic infection, clinical endpoints to be used in the design of BE clinical trials, and more accurate classification of patients using phenotypes and endotypes to better guide treatment decisions and improve outcomes.

Immunogenicity and protection against Mycobacterium avium with a heterologous RNA prime and protein boost vaccine regimen

Prophylactic efficacy of two different delivery platforms for vaccination against Mycobacterium avium (M. avium) were tested in this study; a subunit and an RNA-based vaccine. The vaccine antigen, ID91, includes four mycobacterial antigens: Rv3619, Rv2389, Rv3478, and Rv1886. We have shown that ID91+GLA-SE is effective against a clinical NTM isolate, M. avium 2-151 smt. Here, we extend these results and show that a heterologous prime/boost strategy with a repRNA-ID91 (replicon RNA) followed by protein ID91+GLA-SE boost is superior to the subunit protein vaccine given as a homologous prime/boost regimen. The repRNA-ID91/ID91+GLA-SE heterologous regimen elicited a higher polyfunctional CD4+ TH1 immune response when compared to the homologous protein prime/boost regimen. More significantly, among all the vaccine regimens tested only repRNA-ID91/ID91+GLA-SE induced IFN-γ and TNF-secreting CD8+ T cells. Furthermore, the repRNA-ID91/ID91+GLA-SE vaccine strategy elicited high systemic proinflammatory cytokine responses and induced strong ID91 and an Ag85B-specific humoral antibody response a pre- and post-challenge with M. avium 2-151 smt. Finally, while all prophylactic prime/boost vaccine regimens elicited a degree of protection in beige mice, the heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen provided greater pulmonary protection than the homologous protein prime/boost regimen. These data indicate that a prophylactic heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen augments immunogenicity and confers protection against M. avium.

Modulating macrophage function to reinforce host innate resistance against Mycobacterium avium complex infection

Mycobacterium avium complex (MAC) is the main causative agent of infectious diseases in humans among nontuberculous mycobacteria (NTM) that are ubiquitous organisms found in environmental media such as soil as well as in domestic and natural waters. MAC is a primary causative agent of NTM-lung disease that threaten immunocompromised or structural lung disease patients. The incidence and the prevalence of M. tuberculosis infection have been reduced, while MAC infections and mortality rates have increased, making it a cause of global health concern. The emergence of drug resistance and the side effects of long-term drug use have led to a poor outcome of treatment regimens against MAC infections. Therefore, the development of host-directed therapy (HDT) has recently gained interest, aiming to accelerate mycobacterial clearance and reversing lung damage by employing the immune system using a novel adjuvant strategy to improve the clinical outcome of MAC infection. Therefore, in this review, we discuss the innate immune responses that contribute to MAC infection focusing on macrophages, chief innate immune cells, and host susceptibility factors in patients. We also discuss potential HDTs that can act on the signaling pathway of macrophages, thereby contributing to antimycobacterial activity as a part of the innate immune response during MAC infection. Furthermore, this review provides new insights into MAC infection control that modulates and enhances macrophage function, promoting host antimicrobial activity in response to potential HDTs and thus presenting a deeper understanding of the interactions between macrophages and MACs during infection.

Increasing and More Commonly Refractory Mycobacterium avium Pulmonary Disease, Toronto, Ontario, Canada

In mid-2014, Public Health Ontario Laboratories identified coincident increasing Mycobacterium avium isolation and falling M. xenopi isolation in the Toronto, Ontario, Canada, area. We performed a retrospective cohort of all patients in a Toronto clinic who began treatment for either M. avium or M. xenopi pulmonary disease during 2009–2012 (early period) or 2015–2018 (late period), studying their relative proportions and sputum culture conversion. We conducted a subgroup analysis among patients who lived in the Toronto-York region. The proportion of patients with M. avium was higher in the late period (138/146 [94.5%] vs. 82/106 [77.4%]; p<0.001). Among M. avium patients, conversion was lower in the late period (26.1% vs. 39.0%; p = 0.05). The increase in the proportion of patients with M. avium pulmonary disease and the reduction in the frequency of sputum culture conversion is unexplained but could suggest an increase in environmental M. avium exposure.

A Comprehensive Review and Update on Epidemiology, Symptomatology and Management of Nontuberculous Mycobacteria (NTM)

Nontuberculous mycobacteria (NTM) are free-living organisms ubiquitously present in the environment. In recent times, NTM gained much importance due to the increase in incidence globally. They are potential agents in causing both pulmonary and extrapulmonary infections in both immunocompromised and immunocompetent individuals. The problem arises when the possible NTM cases are misdiagnosed as drug-resistant tuberculosis (DR-TB). Hence, it is essential to correctly identify the NTMs causing disease due to two major reasons. One is to prevent clinicians from starting anti-tuberculous drugs and the other is that treatment regimen differs for certain NTM from tuberculosis. Apart from conventional methods like smear microscopy, culture, in the current era newer diagnostic modalities like matrix-assisted laser desorption of ionization-time of flight mass spectrometry (MALDI TOF MS), line probe assay, genomic sequencing, are used in referral laboratories which allows identification and speciation of the organism. A thorough literature search was done in PubMed, Google Scholar, Cochrane Library, Embase, Scopus on nontuberculous mycobacteria. The search keywords include nontuberculous mycobacteria, atypical mycobacteria, case reports, and original articles on NTM. In this review, we have summarised the current knowledge on epidemiology, pathogenesis, clinical features, and treatment of NTM.

Meeting the challenges of NTM-PD from the perspective of the organism and the disease process: innovations in drug development and delivery

Non-tuberculous mycobacterial pulmonary disease (NTM-PD) poses a substantial patient, healthcare, and economic burden. Managing NTM-PD remains challenging, and factors contributing to this include morphological, species, and patient characteristics as well as the treatment itself. This narrative review focusses on the challenges of NTM-PD from the perspective of the organism and the disease process. Morphological characteristics of non-tuberculous mycobacteria (NTM), antimicrobial resistance mechanisms, and an ability to evade host defences reduce NTM susceptibility to many antibiotics. Resistance to antibiotics, particularly macrolides, is of concern, and is associated with high mortality rates in patients with NTM-PD. New therapies are desperately needed to overcome these hurdles and improve treatment outcomes in NTM-PD. Amikacin liposome inhalation suspension (ALIS) is the first therapy specifically developed to treat refractory NTM-PD caused by Mycobacterium avium complex (MAC) and is approved in the US, EU and Japan. It provides targeted delivery to the lung and effective penetration of macrophages and biofilms and has demonstrated efficacy in treating refractory MAC pulmonary disease (MAC-PD) in the Phase III CONVERT study. Several other therapies are currently being developed including vaccination, bacteriophage therapy, and optimising host defences. Newly developed antibiotics have shown potential activity against NTM-PD and include benzimidazole, delamanid, and pretomanid. Antibiotics commonly used to treat other infections have also been repurposed for NTM-PD, including clofazimine and bedaquiline. Data from larger-scale studies are needed to determine the potential of many of these therapies for treating NTM-PD.

Pulmonary nontuberculous mycobacterial infections and environmental factors: A review of the literature

BACKGROUND

Pulmonary nontuberculous mycobacterial (pNTM) infection is mainly acquired through the inhalation of bioaerosols. Nevertheless, behavioural restrictions are rarely given by clinicians to susceptible populations, in part because the available guidelines for pNTM management emphasize more diagnosis and treatment than prevention. Aim of this review is to clarify if pNTM prevention should routinely include recommendations about risk reducing behaviors.

METHODS

We used PubMed as biomedical database. We limited our search to the publication period 2000 to 2020 with selected keyword combinations including "nontuberculous mycobacteria", "water", "soil", and "exposure". Titles and abstract of selected articles were systematically screened. Articles were included in the analysis if they were published under free access through the digital library of the University of Brescia (Italy), and provided full text either in English, French, German or Italian. Articles were excluded if the topic was beyond the aim of our study. Finally, we selected 20 articles.

RESULTS

Studies disagree in identifying the type of aerosol posing the highest risk for the development of pNTM infection. In the retrieved publications the colonization of household niches has been associated with a higher risk of pNTM disease, such as in the exposure to shower aerosols. Considering the non-household settings, the exposure to aerosols in indoor swimming and the higher soil exposure (>2 h/week) seem to correlate with a higher risk to develop pNTM disease. According to our findings, randomized behavioural intervention studies are missing.

CONCLUSIONS

Stringent scientific evidence is missing to formulate recommendations on behavioural risk reduction for pNTM.

Challenges of diagnosing and treating non-tuberculous mycobacterial pulmonary disease [NTM-PD]: A case series

Non-tuberculous mycobacterial pulmonary disease (NTM-PD) may simulate Pulmonary Tuberculosis (PTB) in its clinical and radiological expression posing a diagnostic dilemma and challenge to the treating physician, especially in high TB prevalent countries. Though recent emerging data indicates inter-human transmission, infection with non-tuberculous mycobacteria (NTM) is commonly acquired from the environmental sources [1]. NTM can produce disease not only in immunocompromised populations but also in healthy individuals leading to significant morbidity and mortality [2]. Unlike PTB, NTM-PD is usually difficult to confirm and speciate in resource limited clinical settings and high TB endemic countries due to non-availability, poor accessibility and affordability to a specific culture facility. Apart from diagnostic challenges, adverse drug effects with treatment leading to non-adherence are another vexing problem. We present here case descriptions of four patients of NTM-PD, confirmed by culture isolates, one was a rapid grower and the other three were slow growers. All four patients were treated with available guideline-based treatment protocols and followed up.

The Association between Behavioral Risk Factors and Nontuberculous Mycobacterial Pulmonary Disease

PURPOSE

We aimed to determine the relationship between environmental exposure and nontuberculous mycobacterial pulmonary disease (NTM-PD) in Korea.

MATERIALS AND METHODS

A group of 150 patients with NTM-PD and a control group of 217 patients with other respiratory diseases were prospectively enrolled between June 2018 and December 2020 in Seoul, Korea. They were surveyed with a standardized questionnaire, and their medical records were reviewed. Odds ratio (OR) and 95% confidence intervals (CI) were calculated with multivariate logistic regression analysis.

RESULTS

The mean ages of the NTM-PD and control groups were similar (63.8±9.2 years vs. 63.5±10.0 years; p=0.737), and most patients were female (76.0% vs. 68.7%; p=0.157) and nonsmokers (82.0% vs. 72.8%; p=0.021). Mycobacterium avium (49.3%) was the most commonly identified strain among NTM-PD patients, followed by M. intracellulare (32.0%) and M. abscessus subspecies massiliense (12.7%). There were no differences in housing type or frequency of soil- or pet-related exposure between the case and the control groups. However, in subgroup analysis excluding patients with M. intracellulare infection, more case patients frequently visited public baths ≥1 time/week (35.3% vs. 19.4%, p=0.003); this remained significant after multivariate analysis (OR, 2.84; 95% CI, 1.58-5.17).

CONCLUSION

Frequent exposure to water at public baths might affect the odds of contracting NTM-PD, excluding individuals infected with M. intracellulare strains.

Subunit vaccine protects against a clinical isolate of Mycobacterium avium in wild type and immunocompromised mouse models

The nontuberculous mycobacteria (NTM) Mycobacterium avium is a clinically significant pathogen that can cause a wide range of maladies, including tuberculosis-like pulmonary disease. An immunocompromised host status, either genetically or acutely acquired, presents a large risk for progressive NTM infections. Due to this quietly emerging health threat, we evaluated the ability of a recombinant fusion protein ID91 combined with GLA-SE [glucopyranosyl lipid adjuvant, a toll like receptor 4 agonist formulated in an oil-in-water stable nano-emulsion] to confer protection in both C57BL/6 (wild type) and Beige (immunocompromised) mouse models. We optimized an aerosol challenge model using a clinical NTM isolate: M. avium 2-151 smt, observed bacterial growth kinetics, colony morphology, drug sensitivity and histopathology, characterized the influx of pulmonary immune cells, and confirmed the immunogenicity of ID91 in both mouse models. To determine prophylactic vaccine efficacy against this M. avium isolate, mice were immunized with either ID91 + GLA-SE or bacillus Calmette-Guérin (BCG). Immunocompromised Beige mice displayed a delayed influx of innate and adaptive immune cells resulting in a sustained and increased bacterial burden in the lungs and spleen compared to C57BL/6 mice. Importantly, both ID91 + GLA-SE and BCG vaccines significantly reduced pulmonary bacterial burden in both mouse strains. This work is a proof-of-concept study of subunit vaccine-induced protection against NTM.

Environmental risk factors associated with pulmonary isolation of nontuberculous mycobacteria, a population-based study in the southeastern United States

The prevalence of pulmonary nontuberculous mycobacteria (NTM) disease is increasing in the United States. Associations were evaluated among residents of central North Carolina between pulmonary isolation of NTM and environmental risk factors including: surface water, drinking water source, urbanicity, and exposures to soils favorable to NTM growth. Reports of pulmonary NTM isolation from patients residing in three counties in central North Carolina during 2006-2010 were collected from clinical laboratories and from the State Laboratory of Public Health. This analysis was restricted to patients residing in single family homes with a valid residential street address and conducted at the census block level (n = 13,495 blocks). Negative binomial regression models with thin-plate spline smoothing function of geographic coordinates were applied to assess effects of census block-level environmental characteristics on pulmonary NTM isolation count. Patients (n = 507) resided in 473 (3.4%) blocks within the study area. Blocks with >20% hydric soils had 26.8% (95% confidence interval (CI): 1.8%, 58.0%), p = 0.03, higher adjusted mean patient counts compared to blocks with ≤20% hydric soil, while blocks with >50% acidic soil had 24.8% (-2.4%, 59.6%), p = 0.08 greater mean patient count compared to blocks with ≤50% acidic soil. Isolation rates varied by county after adjusting for covariates. The effects of using disinfected public water supplies vs. private wells, and of various measures of urbanicity were not significantly associated with NTM. Our results suggest that proximity to certain soil types (hydric and acidic) could be a risk factor for pulmonary NTM isolation in central North Carolina.

Epidemiological risk factors and the geographical distribution of eight Mycobacterium species

Background

Nontuberculous mycobacteria (NTM) are environmental bacterium that may cause and/or compound respiratory diseases in humans. There are over a hundred NTM species with varying pathogenicity’s Therefore, it is necessary to characterize the populations at risk for each species.

Methods

Demographic (age, sex, and state of residence) and microbiological data from 2014 were extracted from Mississippi, Missouri, and Ohio disease surveillance systems. NTM species with > 50 reports were included in the analysis. Patient sex, age, and incidence rates were generated for each of the following NTM species: M. abscessus, M. avium complex (MAC), M. chelonae, M. fortuitum, M. gordonae, M. kansasii, M. mucogenicum, and M. peregrinum.

Results

Analysis by sex showed that M. chelonae,M. fortuitum, M. gordonae,and M. kansasii had significantly higher rates in males than females. Age was not associated with patient rates for several specific NTM species e.g., M. chelonae. Mississippi had the highest patient’ rates for M. avium, M. gordonae, M. kansasii, and M. chelonae. Ohio had the highest patient’ rates for M. abscessus, M. mucogenicum, and M. peregrinum. The highest patient’s rate for M. fortuitum was observed in Missouri.

Conclusion

This study showed that NTM infection occurred more frequently in males. The highest rates were observed in Mississippi for most of the NTMs studied. Age was not a strong risk factor for some of the NTM species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-05925-y.

Impact of body mass index on development of nontuberculous mycobacterial pulmonary disease

The incidence and prevalence of nontuberculous mycobacterial pulmonary disease (NTM-PD) have been increasing worldwide. The risk of NTM-PD may be higher in undernourished populations. In this study, we tried to elucidate the impact of body mass index (BMI) and its change on development of NTM-PD.We performed a retrospective cohort study including South Koreans aged >40 years who underwent biennial National Health Insurance System (NHIS) health check-ups in both 2005 and 2009 or 2006 and 2010. We monitored eligible individuals from the study initiation date (NHIS health check-up date in 2009 or 2010) until the diagnosis of NTM-PD or until December 31, 2017. Enroled individuals were classified based on BMI at initiation date. By calculating hazard ratios, we compared NTM-PD incidence per 100 000 person-years by BMI group and by BMI change.A total of 5 670 229 individuals were included in the final analysis. Compared with the BMI <18.5 kg·m^-2 group, the incidence of NTM-PD gradually decreased with increased BMI (adjusted hazard ratio 0.38, 95% confidence interval (CI) 0.35-0.42 for BMI 18.5-22.9; 0.17, 95% CI 0.15-0.19 for BMI 23-24.9; 0.1, 95% CI 0.09-0.11 for BMI 25-29.9; and 0.1, 95% CI 0.07-0.13 for BMI ≥30). A BMI decrease of ≥1 kg·m^-2 over 4 years increased the incidence of NTM-PD (adjusted hazard ratio 1.08, 95% CI 1.01-1.16) whereas a BMI increase of ≥1 kg·m^-2 decreased the incidence of NTM-PD (adjusted hazard ratio 0.77, 95% CI 0.71-0.83).In conclusion, BMI was inversely related to development of NTM-PD and weight loss increased the risk of NTM-PD.

Correlation between serum carbohydrate antigen 19-9 levels and computed tomography severity score in patients with nontuberculous mycobacterial pulmonary disease

There is no validated clinical biomarker for disease severity or treatment response for nontuberculous mycobacterial pulmonary disease (NTM-PD). We investigated the correlation between elevated serum carbohydrate antigen (CA) 19-9 levels and NTM-PD disease activity, defined using an imaging severity score based on chest computed tomography (CT). We retrospectively examined 79 patients with NTM-PD who underwent serum CA19-9 level assessments and chest CT less than 1 month apart. NTM-PD severity was rated using a CT-based scoring system. The correlation between the CT score and serum CA19-9 levels was evaluated. Chest CT revealed nodular bronchiectasis without cavitation in most patients (78.5%). Serum CA19-9 levels were elevated in 19 (24%) patients. Serum CA19-9 levels were positively correlated with the total CT score and bronchiectasis, bronchiolitis, cavity, and consolidation subscores. Partial correlation analysis revealed a significant positive correlation between serum CA19-9 levels and CT scores for total score and bronchiectasis, bronchiolitis, cavitation, and consolidation subscores after controlling for age, sex, and BMI. Serum CA19-9 levels were positively correlated with the CT severity score for NTM-PD. Serum CA19-9 may be useful in evaluating disease activity or therapeutic response in patients with NTM-PD.

Association between Mycobacterium avium Complex Pulmonary Disease and Mycobacteria in Home Water and Soil

Rationale: Nontuberculous mycobacteria (NTM), including Mycobacterium avium complex (MAC), are emerging pathogens that can opportunistically cause debilitating pulmonary disease in susceptible human hosts. Potential sources of exposure in homes include point-of-use water sources, such as taps and showerheads, as well as gardening soils. The relative human health impacts of NTM in these home environments remain poorly understood.Objectives: This study tested associations between MAC pulmonary disease and NTM colonization of five potential point-of-use sources of pathogen exposure in homes.Methods: A case-control study was conducted of Washington and Oregon residents who had been diagnosed with MAC pulmonary disease, and population controls were matched by age, sex, and geography. Samples were collected from bathroom faucets, kitchen faucets, shower aerosols, indoor soil, and outdoor soil. Mycobacteria in environmental samples were identified in a blinded fashion by using bacteriological culture combined with polymerase chain reaction. The isolation of NTM from case homes (n = 56) versus control homes (n = 51) was quantitatively compared using conditional logistic regression models with adjustment for potential confounding variables.Results: NTM were isolated from shower aerosols collected in case homes more often than in control homes. An adjusted conditional logistic regression analysis showed that NTM isolation from shower aerosols had a high odds ratio associated with disease (odds ratio, 4.0; 95% confidence interval, 1.2-13). Other home environmental samples (tap water, soils) did not exhibit this association.Conclusions: The results implicate shower aerosols as uniquely significant sources of NTM exposure in homes.

A case of relapsed Mycobacterium chelonae pulmonary infection presenting with severe weight loss and treated with a combination of antibiotic therapy and percutaneous feeding

Mycobacterium chelonae is a type of nontuberculous mycobacteria most commonly associated with skin and soft tissue infections. We present a case of recurrent M. chelonae pulmonary infection presenting with severe weight loss. After recurrence, sputum cultures remained positive for 2 years despite appropriate antibiotics. Cultures only became negative after the addition of intravenous imipenem and jejunostomy feeds. The rarity of M. chelonae pulmonary infection means that optimal treatment regimens have not yet been fully established but a regimen of clarithromycin plus an additional antibiotic has been recommended¹. The prognosis of such infections also remains unclear but lower rates of macrolide resistance suggest that the prognosis may be better than the closely related species M. abscessus. Although its benefit has not been proven, nutrition supplementation, including percutaneous enteral feeding, can be considered for refractory NTM infection in underweight patients.

Mycobacterium avium Complex: Addressing Gaps in Diagnosis and Management

Nontuberculous mycobacteria (NTM) are ubiquitous in the environment and an important cause of disease. The most common species causing pulmonary disease are members of Mycobacterium avium complex (MAC). MAC pulmonary disease (MAC-PD) can be chronic, debilitating, costly, and associated with a high mortality. However, MAC diagnoses are often delayed due to the nonspecific presentation of MAC-PD and radiological findings that overlap with other pulmonary diseases. Patients with risk factors and who meet the diagnostic criteria-which include clinical, radiological, and microbiologic criteria-should be considered for treatment. Diagnosis requires 2 or more positive sputum cultures or 1 bronchoscopic specimen culture. The recommendation for those who are treated is a 3-drug regimen including macrolide, rifamycin, and ethambutol that is continued for 12 months beyond sputum culture conversion to negative. MAC-PD is difficult to treat, with frequent drug-related side effects and suboptimal treatment outcomes. Refractory and recurrent disease is common, leading to lifelong follow-up of patients. There are limited treatment options for patients with macrolide-resistant or refractory disease. Amikacin liposome inhalation suspension is recommended for treatment-refractory patients whose cultures remain positive after 6 months of guideline-based therapy. Among the research priorities to improve patient outcomes and quality of life are developing new, more rapid diagnostic tests, investigating biomarkers associated with disease progression, and identifying new drugs and routes of administration as well as new, shorter, and better-tolerated regimens.

Mycobacterium avium complex infection in a patient with systemic sclerosis- associated interstitial lung disease: A case report

We describe a case of a 65-year-old male with recently diagnosed diffuse cutaneous systemic sclerosis associated with usual interstitial pneumonia and pulmonary hypertension. Patient presented to the emergency department complaining of low-grade fever, increased sputum production, progressive dyspnea and weight loss. High-resolution computed tomography scan showed multifocal bronchiectasis with multiple small nodules. Bronchoalveolar lavage culture was positive for Mycobacterium intracellulare. Antimicrobial treatment was started which improved respiratory symptoms. One month after the initiation of antibiotics, cyclophosphamide therapy was started with adequate tolerance.

Nontuberculous Mycobacteria and Heterologous Immunity to Tuberculosis

Development of an improved tuberculosis (TB) vaccine is a high worldwide public health priority. Bacillus Calmette-Guerin (BCG), the only licensed TB vaccine, provides variable efficacy against adult pulmonary TB, but why this protection varies is unclear. Humans are regularly exposed to non-tuberculous mycobacteria (NTM) that live in soil and water reservoirs and vary in different geographic regions around the world. Immunologic cross-reactivity may explain disparate outcomes of BCG vaccination and susceptibility to TB disease. Evidence supporting this hypothesis is increasing but challenging to obtain due to a lack of reliable research tools. In this review, we describe the progress and bottlenecks in research on NTM epidemiology, immunology and heterologous immunity to Mtb. With ongoing efforts to develop new vaccines for TB, understanding the effect of NTM on vaccine efficacy may be a critical determinant of success.

Host immune response against environmental nontuberculous mycobacteria and the risk populations of nontuberculous mycobacterial lung disease

Nontuberculous mycobacterial lung disease (NTM-LD) prevalence has been increasing over the recent decades. Numerous host factors are associated with NTM-LD development, including susceptible phenotypes such as ciliary defect and lung structural change, pulmonary clearance defect with poor clearance of secretions, and immune suppression. Specifically, regarding the susceptible host phenotypes without clear pathogenesis, a slender body, pectus excavatum, and postmenopausal female status are common. Also, decreased host immunity to NTM, especially T helper 1 cell responses is frequently observed. Even so, the underlying mechanisms remain unclear and relevant large-scale studies are lacking. Infections due to host genetics associated defects are mostly untreatable but rare in Asia, particularly Taiwan. Nevertheless, some risks for NTM-LD are controllable over disease progression. We suggest that clinicians first manage host factors and deal with the controllable characteristics of NTM-LD, followed by optimizing anti-NTM treatment. Further researches focusing on NTM-LD pathogenesis, especially the host-NTM interaction may advance understanding the nature of the disease and develop efficient therapeutic regimens.

Epidemiology of Nontuberculous Mycobacteria Infection in Children and Young People With Cystic Fibrosis: Analysis of UK Cystic Fibrosis Registry

Background

Infection with nontuberculous mycobacteria (NTM) is of growing clinical concern in people with cystic fibrosis (CF). The epidemiology of infection in children and young people remains poorly understood. Our goal was to investigate the epidemiology of NTM infection in the pediatric age group using data from the UK CF Registry.

Methods

Data from 2010–2015 for individuals aged <16 years (23200 observations from 5333 unique individuals) were obtained. Univariate analysis of unique individuals comparing all key clinical factors and health outcomes to NTM status was performed. The significant factors that were identified were used to generate a multivariate logistic regression model that, following step-wise removal, generated a final parsimonious model.

Results

The prevalence of individuals with a NTM-positive respiratory culture increased every year from 2010 (45 [1.3%]) to 2015 (156 [3.8%]). Allergic bronchopulmonary aspergillosis (odds ratio [OR], 2.66; P = 5.0 × 10⁻⁸), age (OR, 1.08; P = 3.4 × 10⁻¹⁰), and intermittent Pseudomonas aeruginosa infection (OR, 1.51; P = .004) were significantly associated with NTM infection.

Conclusions

NTM infection is of increasing prevalence in the UK pediatric CF population. This study highlights the urgent need for work to establish effective treatment and prevention strategies for NTM infection in young people with CF.

Preventing infectious complications when treating non-malignant immune-mediated hematologic disorders

Immunosuppressants, targeted antibody therapies, and surgical splenectomy are amongst the treatment choices for immune-mediated non-malignant hematologic disorders, with infection being the most common non-hematological adverse event from these therapies. Corticosteroids are associated with a length-of-treatment and dose-dependent risk for infection, including opportunistic infections. Screening and antimicrobial prophylaxis against tuberculosis, Strongyloides stercoralis, and Pneumocystis jirovecii pneumonia, are indicated in selected patients on steroids and with certain risk factors for infection. Rituximab is associated with hepatitis B virus reactivation. All patients planned to be started on rituximab should be screened for hepatitis B surface antigen and total core antibody, with antiviral prophylaxis given depending on test results. In eculizumab treated patients, immunization against meningococcal serogroups ACWY and B is recommended. In addition, some guidelines suggest antibiotic prophylaxis for the duration of eculizumab treatment. In splenectomized patients, counseling and immunization are cornerstones of infection prevention. Several federal and society guidelines about immunizations and prophylactic antimicrobial therapies for patients treated with various immunosuppressive agents exist and are summarized in this manuscript in a clinical-focused table. In addition, management suggestions are made where no formal guidelines exist.

Association between Inhaled Corticosteroid Use and Pulmonary Nontuberculous Mycobacterial Infection

RATIONALE

Nontuberculous mycobacterial (NTM) pulmonary disease prevalence is increasing.

OBJECTIVES

To determine the association between the use of inhaled corticosteroids and the likelihood of NTM pulmonary infection among individuals with treated airway disease.

METHODS

We conducted a case-control study of subjects with airway disease with and without NTM pulmonary infection (based on mycobacterial respiratory cultures) between 2000 and 2010 in northern California. We quantified the use of inhaled corticosteroids, other airway disease medications, and healthcare use within 6 months of NTM pulmonary infection identification. We used 1:10 case-control matching and conditional logistic regression to evaluate the association between the duration and cumulative dosage of inhaled corticosteroid use and NTM pulmonary infection.

RESULTS

We identified 248 cases with NTM pulmonary infection with an estimated rate of 16.4 cases per 10,000 subjects treated for airway disease. The median interval between treated airway disease cohort entry (defined as date of patient filling the third airway disease treatment prescription) and NTM case identification was 1,217 days. Compared with control subjects, subjects with NTM pulmonary infection were more likely to use airway disease medications including systemic steroids; they were also more likely to use health care. Any inhaled corticosteroids use between 120 days and 2 years before cohort entry was associated with substantially increased odds of NTM infection. For example, the adjusted odds ratio for NTM infection among inhaled corticosteroid users in a 2-year interval was 2.51 (95% confidence interval, 1.40-4.49; P < 0.01). Increasing cumulative inhaled corticosteroid dose was also associated with greater odds of NTM infection.

CONCLUSIONS

Inhaled corticosteroid use, and particularly high-dose inhaled corticosteroid use, was associated with an increased risk of NTM pulmonary infection.

Choroidal granuloma caused by Mycobacterium Fortuitum

Background

To report a case of a chronic steroid user male patient who developed local abscesses caused by M. fortuitum and concomitant asymptomatic choroidal granuloma.

Case presentation

A 37-year-old african-american male with history of use of anabolic drugs and intramuscular mineral oil injections in the upper and lower limbs for 15 years for muscular hypertrophy. He developed intramuscular abscesses with systemic infection, sub-retinal lesions in both eyes and alterations in cerebrospinal fluid suggestive of mycobacteria. Considering these findings, empirical treatment for tuberculosis was started, without success. After several negative cultures of the material drained from the abscesses, finally one of the cultures isolated the agent Mycobacterium Fortuitum. Proper treatment for atypical mycobacteria was initiated with clinical and laboratory improvement. After 6 months the sub-retinal lesions regressed.

Conclusions

A typical choroidal granuloma caused by M. Fortuitum is a rare presentation of the infection and our report showed a good outcome with proper treatment.

Socio-Economic and Environmental Factors Related to Spatial Differences in Human Non-Tuberculous Mycobacterial Diseases in the Czech Republic

Non-tuberculous mycobacteria (NTM) are ubiquitous environmental bacteria that can induce pulmonary and non-pulmonary diseases in susceptible persons. It is reported that the prevalence of NTM diseases is increasing in developed countries, but this differs by regions and countries. NTM species distribution and the rate of diseases caused by NTM vary widely in the historical territories of Moravia and Silesia (Czech Republic). This epidemiologic study of NTM diseases covers the period 2012–2018, reviews isolates obtained from patients with clinical disease and investigates correlations with related socio-economic and environmental factors. Individual NTM patients were included only once during the studied period and results were presented as incidence rate per year. The most frequently isolated NTM meeting the microbiological and clinical criteria in the study were the Mycobacterium avium-intracellulare complex, followed by Mycobacterium kansasii and Mycobacteriumxenopi. A previously described endemic incidence of M.kansasii in the Karviná district and M.xenopi in the Ostrava district was also observed in this study. The incidence of NTM patients in the whole studied territory was 1.10/100,000 inhabitants (1.33/100,000 in men and 0.88/100,000 in women). The annual incidence of lymphadenitis in children (≤5 years of age) was 2.35/100,000 of the population of children during the 7 year period but increased in the year 2018 to 5.95/100,000. The rate of human tuberculosis in the studied area was 1.97/100,000 inhabitants. The incidence of NTM pulmonary diseases correlated with a lower socio-economic status (r = 0.63) and a higher concentration of benzo[a]pyrene pollution in the air (r = 0.64).

Management of infections due to nontuberculous mycobacteria in solid organ transplant recipients-Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the American Society of Transplantation Infectious Diseases Community of Practice review the epidemiology, diagnosis, prevention, and management of nontuberculous mycobacterial infections in the pre- and post-transplant period. NTM commonly cause one of five different clinical syndromes: pleuropulmonary disease, skin and soft tissue infection, osteoarticular infection, disseminated disease, including that caused by catheter-associated infection, and lymphadenitis. Diagnosis of these infections can be challenging, particularly when they are isolated from nonsterile spaces, owing to their ubiquity in nature. Consequently, diagnosis of pulmonary infections with these pathogens requires fulfillment of microbiologic, radiographic, and clinical criteria to address this concern. A combination of culture and molecular diagnostic techniques is often required to make a species-level identification. Treatment varies depending on the species isolated and is complex, owing to drug toxicities, need for long-term multidrug regimens, and consideration of complex drug-drug interactions between antimicrobials and immunosuppressive agents. Given these treatment challenges, efforts should be made in both the hospital and community settings to limit exposure to these pathogens to the extent feasible.

The complexities and challenges of preventing and treating nontuberculous mycobacterial diseases

Seemingly innocuous nontuberculous mycobacteria (NTM) species, classified by their slow or rapid growth rates, can cause a wide range of illnesses, from skin ulceration to severe pulmonary and disseminated disease. Despite their worldwide prevalence and significant disease burden, NTM do not garner the same financial or research focus as Mycobacterium tuberculosis. In this review, we outline the most abundant of over 170 NTM species and inadequacies of diagnostics and treatments and weigh the advantages and disadvantages of currently available in vivo animal models of NTM. In order to effectively combat this group of mycobacteria, more research focused on appropriate animal models of infection, screening of chemotherapeutic compounds, and development of anti-NTM vaccines and diagnostics is urgently needed.

Risk factors for developing Mycobacterium kansasii lung disease: A case-control study in Korea

Previous studies have suggested that development of Mycobacterium kansasii lung disease (MKLD) was associated with COPD, pneumoconiosis, aging, male, immunosuppression, alcohol, malignancy, and certain occupations such as mining and sandblasting. However, previous studies were outdated and used non-comparative statistical methods. We aimed to determine the current risk factors for developing MKLD in Korea by using appropriate statistical techniques.Eighty-six MKLD patients were identified through a search of the Ulsan University Hospital database between January 2010 and December 2014. These cases were matched with 172 controls who had normal respiratory systems in a health examination during the same period (matching variables, age and sex; case: control ratio of 1:2). Clinical and demographic characteristics were gathered by reviewing the medical record and telephone survey. Multivariate logistic regression analyses were performed to evaluate risk factors for developing MKLD.Multivariate analysis showed that occupation in heavy industries (adjusted odds ratio (aOR) 6.41, 95% confidence interval (CI) 2.19-18.74, P = .001) and low body mass index (BMI) (aOR [per kg/m] 0.73, 95% CI 0.63-0.85, P < .001) were independent risk factors for development of MKLD. Educational attainment more than high school was associated with a lower risk of MKLD development (aOR 0.22, 95% CI 0.08-0.63, P = .005).Employees in heavy industry and low BMI are independent risk factors for development of MKLD in Korea.

Mycobacterium avium paratuberculosis and Mycobacterium avium complex and related subspecies as causative agents of zoonotic and occupational diseases

Mycobacterium avium complex (MAC) and Mycobacterium avium paratuberculosis (MAP) cause zoonotic infections transmitted by birds and livestock herds. These pathogens have remained as serious economic and health threats in most areas of the world. As zoonotic diseases, the risk of development of occupational disease and even death outcome necessitate implementation of control strategies to prevent its spread. Zoonotic MAP infections include Crohn's disease, inflammatory bowel disease, ulcerative colitis, sarcoidosis, diabetes mellitus, and immune-related diseases (such as Hashimoto's thyroiditis). Paratuberculosis has classified as type B epidemic zoonotic disease according to world health organization which is transmitted to human through consumption of dairy and meat products. In addition, MAC causes pulmonary manifestations and lymphadenitis in normal hosts and human immunodeficiency virus (HIV) progression (by serotypes 1, 4, and 8). Furthermore, other subspecies have caused respiratory abscesses, neck lymph nodes, and disseminated osteomyelitis in children and ulcers. However, the data over the occupational relatedness of these subspecies is rare. These agents can cause occupational infections in susceptible herd breeders. Several molecular methods have been recognized as proper strategies for tracking the infection. In this study, some zoonotic aspects, worldwide prevalence and control strategies regarding infections due to MAP and MAC and related subspecies has been reviewed.

Risk factors and secondary care utilisation in a primary care population with non-tuberculous mycobacterial disease in the UK

Prior research has identified risk factors associated with developing non-tuberculous mycobacterial disease (NTMD); we identified risk factors and secondary care utilisation of NTMD patients in the UK. This was a matched case-control study using electronic healthcare records from Clinical Practice Research Datalink from 2006 to 2016. NTMD was defined using prescription data and Read codes, based on international guidelines. Risk factors for NTMD were investigated using conditional logistic regression within a representative general population. All-cause secondary care utilisation (combined inpatient, outpatient, emergency visits) was investigated for participants with linked Hospital Episode Statistics (HES), using incidence rate ratio (IRR) from 2007 to 2015. We identified 1225 individuals with NTMD. A subset of individuals (426 patients) were eligible for linkage with HES. In the adjusted model, risk factors most strongly associated with an increased likelihood of NTMD included previous tuberculosis (OR 69.0; 47.7-99.8); bronchiectasis (OR 23.3; 12.4-43.9); lung cancer (OR 14.9; 3.98-55.7); oral corticosteroids (OCS; OR 7.28; 4.94-10.7); immunosuppressive (excluding corticosteroids) medication (OR 3.05; 1.15-8.10); being underweight (odds ratio (OR) 2.92; 95% CI 1.95, 4.36); and rheumatoid arthritis (OR 2.12; 1.05-4.27). NTMD patients had significantly higher rates of all-cause secondary care utilisation than non-NTMD patients (IRR 5.80; 5.14-6.46). Using a representative adult population, we identified prior TB, bronchiectasis, lung cancer, immunosuppressive medication, and OCS as the risk factors associated with the highest odds of developing NTMD in the UK. Patients with NTMD experienced nearly six times more all-cause secondary care events following their NTMD diagnosis than patients without NTMD.

Acquired and genetic host susceptibility factors and microbial pathogenic factors that predispose to nontuberculous mycobacterial infections

Nontuberculous mycobacteria (NTM) are ubiquitous in the environment and human exposure is likely to be pervasive; yet, the occurrence of NTM-related diseases is relatively infrequent. This discrepancy suggests that host risk factors play an integral role in vulnerability to NTM infections. Isolated NTM lung disease (NTM-LD) is often due to underlying anatomical pulmonary or immune disorders, either of which may be acquired or genetic. However, many cases of NTM-LD have no known underlying risk factors and may be multigenic and/or multicausative. In contrast, extrapulmonary visceral or disseminated NTM diseases almost always have an underlying severe immunodeficiency, which may also be acquired or genetic. NTM cell wall components play a key role in pathogenesis and as inducers of the host immune response.

Are We Neglecting Nontuberculous Mycobacteria Just as Laboratory Contaminants? Time to Reevaluate Things

OBJECTIVES

Nontuberculous mycobacteria (NTM) incidences are on the rise worldwide, including the tuberculosis endemic areas. They should be identified rapidly to the species level and should be carefully differentiated as contamination, colonization, or disease. This study was aimed at determining the prevalence and clinicoepidemiological profile of mycobacteriosis cases.

MATERIALS AND METHODS

Cultures were made on liquid and solid media. NTM were identified by polymerase chain reaction (PCR) restriction analysis (PRA) and gene sequencing. Data was analyzed using Epi-info 7.

RESULTS

Out of the 1042 processed specimens, 16% were positive for M. tuberculosis complex and 1.2% for clinically significant NTM. M. intracellulare was the commonest species isolated. NTM were treated mainly on outdoor basis (92%), involving more extrapulmonary system (62%) and higher age-group of 41-60 years (69%). No significant factor was seen to be associated clinically, radiologically, and biochemically with the NTM infections.

CONCLUSIONS

Our study highlights the importance of early diagnosis and differentiation among Mycobacterium tuberculosis and NTM so that these NTM are not underestimated in routine diagnostic procedures merely as environmental or laboratory contaminants.

A Geospatial Epidemiologic Analysis of Nontuberculous Mycobacterial Infection: An Ecological Study in Colorado

RATIONALE

Nontuberculous mycobacteria (NTM) are ubiquitous environmental microorganisms. Infection is thought to result primarily from exposure to soil and/or water sources. NTM disease prevalence varies greatly by geographic region, but the geospatial factors influencing this variation remain unclear.

OBJECTIVES

To identify sociodemographic and environmental ecological risk factors associated with NTM infection and disease in Colorado.

METHODS

We conducted an ecological study, combining data from patients with a diagnosis of NTM disease from National Jewish Health's electronic medical record database and ZIP code-level sociodemographic and environmental exposure data obtained from the U.S. Geological Survey, the U.S. Department of Agriculture, and the U.S. Census Bureau. We used spatial scan methods to identify high-risk clusters of NTM disease in Colorado. Ecological risk factors for disease were assessed using Bayesian generalized linear models assuming Poisson-distributed discrete responses (case counts by ZIP code) with the log link function.

RESULTS

We identified two statistically significant high-risk clusters of disease. The primary cluster included ZIP codes in urban regions of Denver and Aurora, as well as regions south of Denver, on the east side of the Continental Divide. The secondary cluster was located on the west side of the Continental Divide in rural and mountainous regions. After adjustment for sociodemographic, drive time, and soil variables, we identified three watershed areas with relative risks of 12.2, 4.6, and 4.2 for slowly growing NTM infections compared with the mean disease risk for all watersheds in Colorado. This study population carries with it inherent limitations that may introduce bias. The lack of complete capture of NTM cases in Colorado may be related to factors such as disease severity, education and income levels, and insurance status.

CONCLUSIONS

Our findings provide evidence that water derived from particular watersheds may be an important source of NTM exposure in Colorado. The watershed with the greatest risk of NTM disease contains the Dillon Reservoir. This reservoir is also the main water supply for major cities located in the two watersheds with the second and third highest disease risk in the state, suggesting an important possible source of infection.

Epidemiology of Nontuberculous Mycobacteriosis

Annual prevalence estimates for pulmonary nontuberculous mycobacterial (PNTM) disease in the contiguous United States range from 1.4 to 13.9 per 100,000 persons, while one study found an annual prevalence of up to 44 per 100,000 persons in Hawaii. PNTM prevalence varies by region, sex, and race/ethnicity, with higher prevalence among women and persons of Asian ancestry, as well as in the Southern United States and Hawaii. Studies consistently indicate that PNTM prevalence is increasing, with estimates ranging from 2.5 to 8% per year. Most PNTM disease is associated with Mycobacterium avium complex (MAC), although the proportion of disease attributed to MAC varies by region. Host factors identified as influencing disease risk include structural lung disease, immunomodulatory medication, as well as variants in connective tissue, mucociliary clearance, and immune genes. Environmental variables including measures of atmospheric moisture and concentrations of certain soil factors have also been shown to correlate with higher PNTM prevalence. Prevalence of extrapulmonary NTM disease is lower, stable, and associated with different risk factors, including primary immune deficiencies or HIV infection.

Patient-Centered Research Priorities for Pulmonary Nontuberculous Mycobacteria (NTM) Infection. An NTM Research Consortium Workshop Report

Nontuberculous mycobacteria (NTM) cause an increasingly important chronic and debilitating lung disease in older adults. Diagnosis is often delayed, although awareness among clinicians and patients is increasing. When necessary, treatment often lasts 18-24 months and consists of three or four antibiotics that can have serious side effects. Relapses are common and commonly require resumption of prolonged therapy. Given the need for improved diagnostic techniques and clinical trials to identify new therapies or to improve existing therapies, a group of North American clinicians and researchers formed the NTM Research Consortium (NTMRC) in 2014. The NTMRC recognized the importance of including the patient voice in determining research priorities for NTM. In November 2015, patients, caregivers, patient advocates, clinical experts, and researchers gathered for a 1-day meeting in Portland, Oregon funded by the Patient-Centered Outcomes Research Institute. The meeting goal was to define patient-centered research priorities for NTM lung infections. Patients expressed frustration with the number of people who have endured years of missed diagnoses or inadequate treatment of NTM. Participants identified as top research priorities the prevention of NTM infection; approval of more effective treatments with fewer side effects and easier administration; understanding the best chest physiotherapy methods; validating and using tools to measure quality of life; and developing a disease-specific activity and severity assessment tool. Workshop participants agreed that two complementary objectives are critical to ensure the best achievable outcomes for patients: (1) additional clinician education to improve screening and diagnosis of NTM infections; and (2) development of a geographically distributed network of experts in NTM disease to offer consultation or direct therapy after a diagnosis is made.

Mycobacterium avium Complex Disease

Despite the ubiqitous nature of Mycobacterium avium complex (MAC) organisms in the environment, relatively few of those who are infected develop disease. Thus, some degree of susceptibility due to either underlying lung disease or immunosuppression is required. The frequency of pulmonary MAC disease is increasing in many areas, and the exact reasons are unknown. Isolation of MAC from a respiratory specimen does not necessarily mean that treatment is required, as the decision to treatment requires the synthesis of clinical, radiographic, and microbiologic information as well as a weighing of the risks and benefits for the individual patient. Successful treatment requires a multipronged approach that includes antibiotics, aggressive pulmonary hygiene, and sometimes resection of the diseased lung. A combination of azithromycin, rifampin, and ethambutol administered three times weekly is recommend for nodular bronchiectatic disease, whereas the same regimen may be used for cavitary disease but administered daily and often with inclusion of a parenteral aminoglycoside. Disseminated MAC (DMAC) is almost exclusively seen in patients with late-stage AIDS and can be treated with a macrolide in combination with ethambutol, with or without rifabutin: the most important intervention in this setting is to gain HIV control with the use of potent antiretroviral therapy. Treatment outcomes for many patients with MAC disease remain suboptimal, so new drugs and treatment regimens are greatly needed. Given the high rate of reinfection after cure, one of the greatest needs is a better understanding of where infection occurs and how this can be prevented.

Attenuation of lymphocyte immune responses during Mycobacterium avium complex-induced lung disease due to increasing expression of programmed death-1 on lymphocytes

Mycobacterium avium complex-induced lung disease (MAC-LD) becomes important due to its increasing prevalence. Attenuated cellular immunity associated with programmed cell death (PD)-1 may play a pathophysiological role in MAC-LD but lacks of investigation. We enrolled 80 participants in this prospective study, including 50 with MAC-LD and 30 healthy controls. Peripheral blood mononuclear cells (PBMCs), lymphocytes and monocyte-derived macrophages were used for MAC antigen stimulation. Patients with MAC-LD had lower tumor necrosis factor-α and interferon-γ responses compared to the healthy controls in PBMC stimulation assays with MAC bacilli. These responses improved after MAC treatment. The PD-1 and PD ligand expressions and apoptosis were higher in the lymphocytes of the patients with MAC-LD compared to the controls. Both PD-1 and apoptosis on T lymphocytes were significantly increased in the patients with MAC-LD, either by direct MAC stimulation or by MAC-primed macrophage activation. Partially blocking PD-1 and the PD ligand with antagonizing antibodies in the stimulation assay significantly increased the cytokine production of IFN-γ and decreased the apoptosis on T lymphocytes. In conclusion, the patients with MAC-LD have attenuated lymphocyte immunity, which might be associated with increasing activation of PD-1 and PD-1 ligand. Regulating such activation might improve the lymphocytic secretion of IFN-γ and reduce apoptosis.

Dose response models and a quantitative microbial risk assessment framework for the Mycobacterium avium complex that account for recent developments in molecular biology, taxonomy, and epidemiology

Mycobacterium avium complex (MAC) is a group of environmentally-transmitted pathogens of great public health importance. This group is known to be harbored, amplified, and selected for more human-virulent characteristics by amoeba species in aquatic biofilms. However, a quantitative microbial risk assessment (QMRA) has not been performed due to the lack of dose response models resulting from significant heterogeneity within even a single species or subspecies of MAC, as well as the range of human susceptibilities to mycobacterial disease. The primary human-relevant species and subspecies responsible for the majority of the human disease burden and present in drinking water, biofilms, and soil are M. avium subsp. hominissuis, M. intracellulare, and M. chimaera. A critical review of the published literature identified important health endpoints, exposure routes, and susceptible populations for MAC risk assessment. In addition, data sets for quantitative dose-response functions were extracted from published in vivo animal dosing experiments. As a result, seven new exponential dose response models for human-relevant species of MAC with endpoints of lung lesions, death, disseminated infection, liver infection, and lymph node lesions are proposed. Although current physical and biochemical tests used in clinical settings do not differentiate between M. avium and M. intracellulare, differentiating between environmental species and subspecies of the MAC can aid in the assessment of health risks and control of MAC sources. A framework is proposed for incorporating the proposed dose response models into susceptible population- and exposure route-specific QMRA models.