Nontuberculous mycobacterial (NTM) species are mycobacterial species other than those classified to the
Traditionally, pulmonary diseases have been reported to account for up to 94% of cases of NTM disease [
Defining the epidemiology of NTM is challenging for several reasons [
Despite obstacles in the study of the epidemiology of pulmonary NTM, available evidence suggests that the prevalence of pulmonary NTM disease has increased dramatically globally over the past 3 decades [
The aim of this hospital-based study was to determine the incidence of the isolation of NTM and the frequency of various NTM species. We also evaluated the clinical and demographic characteristics of patients with NTM and attempted to identify possible differences between patients colonized with and those who were actually diseased by NTM in terms of comorbidities and use of inhaled corticosteroids.
The study included consecutive adult in- and outpatients assessed at Sismanoglio-A. Fleming General Hospital of Attiki (SGH) from January 2007 through end of May 2013 from whom at least one biological sample was tested culture-positive for NTM. SGH is a 450-bed capacity hospital with a large number of outpatient clinic visits daily and the second largest tertiary referral hospital for patients with respiratory disease in Athens, Greece. SGH has a level II mycobacteriology laboratory with extensive experience in the field also was empowered to conduct limited-scale level III (reference-level) laboratory tasks.
Initial data were gathered from the database of the Department of Biopathology of SGH and included patient identification, species of the isolated NTM, isolation source, and patient demographics as described later. Multiple identical isolates from the same site during the same hospital episode in a single individual were counted as one patient entry. Subsequently, the medical records of these patients were reviewed with the aim of identifying relevant clinical characteristics as described later.
Ethics approval for this study was granted from the Institutional Review Board.
The clinical specimens were decontaminated using N-acetyl-L-cysteine-sodium hydroxide (NALC) in a Type 2 Biosafety Cabinet. All specimens were then inoculated into solid Löwenstein-Jensen (bioMerieux, Marcy, l’ Etoile, France) and into 7H9 Middlebrook Broth Base 0.47% w/v (MGIT, Becton Dickinson, USA) media. Solid medium cultures were incubated in a 37°C incubator for 60 to 70 days and monitored every four days, whereas liquid cultures were incubated in an automated Bactec MGIT-960 (Becton Dickinson, USA) system for 45 days. Cultures exhibiting growth were subjected to light microscopy for the presence of acid-fast bacteria before being considered as positive. All positive cultures were subsequently analyzed by the GenoType Mycobacterium CM (Hain, LifeSciences, Germany) molecular genetic assay for identification of
Patients were considered as having pulmonary NTM disease if they met the clinical, radiological, and microbiological characteristics as defined by the 2007 American Thoracic Society and Infectious Disease Society of America (ATS/IDSA) statement: Diagnosis, Treatment, and Prevention of Nontuberculous Mycobacterial Diseases [
We defined NTM-infected (colonized) subjects as those who had at least one positive culture for NTM without fulfilling the complete diagnostic criteria and without any record of treatment for NTM disease.
Demographic variables included age (at specimen’s collection date), sex, ethnicity, and country of residence.
Clinical characteristics included the principal working diagnosis at the time of the specimen collection and the underlying medical conditions. The underlying conditions evaluated included chronic lung disease such as COPD, asthma, bronchiectasis, and old TB. Other conditions associated with immunosuppression including diabetes mellitus, HIV infection, autoimmune diseases, malignancy, chronic liver disease, and chronic renal disease were also logged. Finally we recorded the smoking status and long-term use of inhaled corticosteroids (ICS) and systemic corticosteroids (CS) prior to the diagnosis (7.5 mg or more of prednisone or equivalent daily for a period of two weeks or longer).
Categorical variables are presented as
The incidence of pulmonary infection and disease caused by NTM for the duration of our study was calculated as the total number of patients with pulmonary NTM infection and disease divided by the total number of patients who attended SGH, including inpatients and outpatients.
All tests were two-tailed and
A total of 132 patient entries with at least one positive culture for NTM from any site per hospital episode were identified. The majority of the identified subjects (95%) were inpatients in the respiratory medicine departments. Eight entries (6%) referred to NTM isolates in gastric fluid, ascitic fluid, urine, and lymph nodes samples and they were excluded from the analysis. Double entries were identified in four patients: two were tested positive twice for the same respiratory NTM species and two were tested positive twice for different respiratory species (all on separate hospital episodes). Therefore, we report on a total of 120 patients who had NTM species isolated from the respiratory system and they were included in the microbiological and epidemiological analysis. We were able to retrieve the medical records of 74 (61%) out of 120 patients; thus the analysis on clinical characteristics is relevant to only this subgroup of patients (Figure
(a) Study population; demographic characteristics (120 Patients). (b) Study population; clinical Characteristics (74 patients).
Gender | |
Females | 76 (63%) |
Males | 44 (37%) |
Total age (years) | 69.9 ± 15.4 |
Age group | |
<20 years | 0 (0%) |
20–40 years | 10 (8%) |
40–60 years | 12 (10%) |
>60 years | 98 (82%) |
Ethnicity | |
Greek | 110 (92%) |
Others (including Middle East, East |
10 (8%) |
Residence | |
Greece | 120 (100%) |
All | Colonized |
Diseased |
|
|
---|---|---|---|---|
Chronic lung disease | ||||
COPD | 32 (43%) | 26 (42%) | 6 (50%) | 0.606 |
Bronchiectasis | 25 (33%) | 22 (35%) | 3 (25%) | 0.635 |
Asthma | 5 (6%) | 4 (6.4%) | 1 (8.3%) | 0.892 |
Cystic fibrosis | 1 (1.3%) | 1 (1.6%) | 0 (0%) | 0.683 |
Old TB | 13 (17%) | 8 (13%) | 5 (41%) | 0.030 |
Use of CS | ||||
Inhaled CS | 23 (32%) | 20 (32%) | 3 (25%) | 0.528 |
Systemic CS | 10 (14%) | 10 (16%) | 0 (0%) | 0.140 |
Smoking habit | ||||
Current or ex-smokers | 44 (59%) | 37 (59%) | 7 (58%) | 0.221 |
Never being smokers | 30 (41%) | 25 (40%) | 5 (42%) | 0.223 |
Others | ||||
HIV | 0 | 0 | 0 | N/A |
Autoimmune |
1 (1.3%) | 1 (1.6%) | 0 (0%) | 0.683 |
Data are presented as mean ± standard deviation (SD) for numerical variables or as number (%) for categorical variables.
COPD: chronic obstructive pulmonary disease, HIV: human immunodeficiency virus, and CS: corticosteroid.
Flowchart of the study population.
The study population consisted of 63% men, with a median age of 69.9 years, with the majority being born in Greece. The prevalence of NTM isolation increased with age, ranging from 0% in patients younger than 20 years to 82% in patients aged >60 years.
Out of the 74 patients included in the clinical analysis, 66% (
One hundred and twenty-two NTM isolates were identified. Only ten percent (
NTM isolates from all sites.
2007 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 | Total number | |
---|---|---|---|---|---|---|---|---|
Rapidly growing NTM | ||||||||
|
6 | 2 | 6 | 0 | 1 | 0 | 0 | 15 (12.2) |
|
2 | 1 | 1 | 0 | 2 | 0 | 0 | 6 (4.9) |
|
2 | 0 | 0 | 0 | 0 | 1 | 0 | 3 (2.4) |
|
0 | 0 | 0 | 0 | 1 | 0 | 1 | 2 (1.6) |
|
0 | 1 | 0 | 1 | 0 | 0 | 0 | 2 (1.6) |
|
0 | 1 | 0 | 0 | 0 | 0 | 0 | 1 (0.8) |
|
0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 (0.8) |
Slowly growing NTM | ||||||||
|
2 | 2 | 0 | 3 | 5 | 2 | 3 | 17 (13.9) |
|
1 | 3 | 2 | 2 | 5 | 3 | 0 | 16 (13.1) |
|
2 | 1 | 2 | 2 | 2 | 3 | 0 | 12 (9.8) |
|
1 | 0 | 3 | 1 | 0 | 1 | 0 | 6 (4.9) |
|
2 | 0 | 1 | 0 | 0 | 0 | 0 | 3 (2.4) |
|
1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 (0.8) |
Unidentified NTM | 7 | 3 | 9 | 4 | 6 | 6 | 2 | 37 (30.3) |
Total per year |
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Diversity of isolated nontuberculous mycobacteria (NTM). RGM: rapidly growing, SGM: slowly growing.
In an attempt to identify the frequency of NTM isolates compared to that of
During the 65-month study period, 138.951 inpatients and 492.845 outpatients where treated at SGH. Accordingly, the incidence of NTM pulmonary infection and disease for the study period was 18.9/100.000 and 8.8/100.000 patients, respectively.
During the 65-month period of our study, a total of 120 patients were identified with at least one positive culture for respiratory NTM isolate and 56 patients fulfilled the microbiological criteria of the ATS/IDSA for NTM disease. The predominant NTM species were MAC (
To our knowledge, this is the first study on the epidemiology of NTM performed in Athens, Greece. Two additional studies on the incidence of NTM in Greece were found in the literature: one conducted in Larissa, central Greece [
In our study, 94% percent of the isolates stemmed from respiratory specimens. This is similar to other studies reporting that around 90% of all NTM isolates were of respiratory origin [
As an alternative method for the epidemiological analysis of the NTM many laboratory-based studies relied upon the microbiological criteria of the ATS/IDSA case definition (validated positive predictive value 85% [
In line with aforementioned evidence, we report a higher number of patients who fulfilled the microbiological criteria of the ATS/IDSA for NTM disease compared to those who fulfilled the complete microbiological, radiological, and clinical criteria for NTM disease. Specifically, of patients with adequate data, only 37.5% of those who fulfilled the microbiological criteria of NTM infection also fulfilled the complete criteria for NTM disease. Another single-centered retrospective analysis reported similar proportion of patients (33%) who fulfilled all ATS/IDSA criteria for NTM disease out of the total number of patients with pulmonary NTM isolates [
In the present study, no statistically significant trends were observed in the yearly incidence of NTM from 2007 to 2013. However, a unifying finding in all the aforementioned studies was that the prevalence of pulmonary NTM infection and/or disease steadily increased during the study time period [
Virtually all studies from industrialized countries (including US, Canada, and Germany) that drew comparisons between the incidence and/or prevalence of pulmonary NTM disease and TB reported significantly higher rates for NTM [
The distribution of NTM species worldwide varies by geographic region [
In terms of gender distribution of pulmonary NTM disease, there has been a gradual shift since early epidemiological data [
In our study, no statistically significant differences were identified between colonized and diseased patients in terms of demographics and other well-documented risk factors for pulmonary NTM disease, including chronic lung disease, nonpulmonary comorbidities, immunosuppression [
Finally, we identified a clinically significant minority (25%) of patients who fulfilled the full criteria for pulmonary NTM in whom the diagnosis was missed during their hospital admission. This group of patients did fulfill the complete criteria for NTM disease but, since the microbiological confirmation was not available before their discharge day, they were treated and discharged under the diagnosis of nonspecific lower respiratory tract infection. It is unknown whether they were tracked at a later stage and put on treatment for NTM disease. Indeed, the microbiology cultures for NTM may take prolonged time (up to several days or weeks) to turn positive. By that time, many patients have been discharged from the hospital and may later not attend their follow-up to system or they may simply be lost in the system. Also, physicians are often reassured by the negativity of fast acid smear in that they will not chase the culture results vigorously and in timely fashion. In our study, culture positivity of the specimens was associated with AFB smear positivity in only 10% of the cases. Consequently, patients may lose their opportunity to be diagnosed with pulmonary NTM disease and receive appropriate treatment. Nevertheless, this finding suggests that NTM disease might be underdiagnosed and thus contributes to the universally reported wide gap in the percentage of the patients with NTM infection and disease.
One study limitation was the fact that only 61% of patient records were retrieved and evaluated. This is of course a universal issue in retrospective record-based studies [
The first data on the epidemiology of NTM in Athens, the capital city of Greece, are presented from the database of a tertiary referral hospital for patients with respiratory disease. From 2007 to 2013, 120 respiratory isolates were identified mostly from patients with chronic respiratory disease. However, only a smaller proportion of patients fulfill the criteria for disease. It is not clear whether the latter truly reflects a low penetration of the disease or underdiagnosis and/or methodological issues. In this study, the diagnosis of pulmonary NTM disease was missed in a clinically significant minority of patients. Increased awareness on behalf of the physicians is required regarding the significant morbidity and mortality of the untreated NTM disease. Moreover full application of the validated clinical, radiological, and microbiological guidelines is imperative in order to correctly identify the cases of NTM disease. This study aspires to increase physicians’ insight into the challenges in the management of patients with potential NTM disease and stimulate further and larger-scale research for better determination of the epidemiology of NTM in Greece and worldwide.
The authors declare that there is no conflict of interests regarding the publication of this paper.