NTM species
From a total of 2145 positive sputum cultures, 1759 isolates, from an equal number of patients, were included in the final analysis (Fig. 1). Of these, 1619 (92.04%) were identified as MTBC and 140 (7.96%) as NTM. A total of 12 different NTM species or species complexes were detected. Isolates belonging to the M. abscessus complex were the most common (n=58, 41.43%), followed by M. sp. VKM Ac-1817D (n=17, 12.14%), M. kansasii (n=16, 11.43%), M. avium (n=13, 9.29%), M. intracellulare (n=13, 9.29%), M. fortuitum (n=6, 4.29%), M. colombiense (n=5, 3.57%), M. marseillense (n=5, 3.57%), M. chimaera (n=4, 2.86%), M. paraintracellulare (n=1, 0.71%), M. sinensis (n=1, 0.71%) and M. sp. YC-RL4 (n=1, 0.71%). Except for M. abscessus, M. fortuitum, M. sinensis, M. sp. VKM Ac-1817D and M. sp. YC-RL4, these isolates were slowly growing mycobacterial species (SGM) [16] (Table 1). Isolates belonging to the M. abscessus complex were not subdivided into species. M. sinensis, synonymous with Mycobacterium sinense, is a multidrug-resistant mycobacteria phylogenetically placed between rapidly growing nontuberculous mycobacteria (RGM) and SGM [17]. M. sp. VKM Ac-1817D [18] and M. sp. YC-RL4 [19] are considered nonpathogenic environmental bacteria and may represent contaminants rather than pathogenic species associated with disease.
Table 1
NTM species identified by Kraken 2 / Bracken (n=140)
Classification
|
Species
|
Number
|
Percentage (%)
|
SGM
|
M. kansasii
|
16
|
11.43
|
|
M. avium
|
13
|
9.29
|
|
M. intracellulare
|
13
|
9.29
|
|
M. colombiense
|
5
|
3.57
|
|
M. marseillense
|
5
|
3.57
|
|
M. chimaera
|
4
|
2.86
|
|
M. paraintracellulare
|
1
|
0.71
|
RGM
|
M. abscessus
|
58
|
41.43
|
|
M. fortuitum
|
6
|
4.29
|
Others
|
M. sp. VKM Ac-1817D
|
17
|
12.14
|
|
M. sp. YC-RL4
|
1
|
0.71
|
|
M. sinensis
|
1
|
0.71
|
Total
|
|
140
|
100
|
SGM: slowly growing nontuberculous mycobacteria; RGM: rapidly growing nontuberculous mycobacteria |
Demographic characteristics and risk factors of NTM infection
Of the 140 individuals with NTM infection, 83 (59.3%) were male and 53 (37.8%) were over 50 years of age (Table 2). 97.7% (1719/1759) of the entire study population were internal migrants to Shenzhen from other regions of China. Univariable logistic regression suggested a significant association of NTM infection with gender, older age, longer period of residence in Shenzhen, retired or unemployed status and prior history of TB. However, after multivariable regression, only longer residence in Shenzhen and prior TB history remained associated with NTM infection. Compared to patients who had lived in Shenzhen for less than 1 year, those who had resided in Shenzhen for more than 2 years had a significantly higher prevalence of NTM than MTBC infections [odds ratio (OR) 4.205; 95% confidence interval (95%CI) 1.851-9.552; P = 0.001]. There was no significant difference in the percentage of NTM vs. MTBC infections in patients who had lived in Shenzhen for 1-2 years (P = 0.065). We also found that the prevalence of NTM infections was significantly higher in patients with a prior history of TB disease than in those with no TB history (OR 4.263; 95% CI 1.871-9.714; P = 0.001). The results of species identification on isolates from 26 patients with 2-3 sputum positive specimens taken at different times showed that in 2 patients the isolates from the initial sputa were identified as MTBC but M. abscessus was found in their follow-up sputa (Supplementary Table S1). In addition, NTM was isolated less frequently than MTBC in patients presenting with cough (OR 0.548; 95% CI 0.310-0.970; P = 0.039). No significant interaction of patients’ age and residence years was observed (P = 0.120).
Table 2
Demographic and clinical characteristics of the 1759 cases with mycobacteria infections
Characteristics
|
No. of mycobacteria infections, n (%)
|
Univariate regression
|
Multivariable regression
|
All
|
MTBC
|
NTM
|
OR (95%CI)
|
P value
|
OR (95%CI)
|
P value
|
Gender
|
|
|
|
|
|
|
|
Female
|
558 (31.7)
|
501 (30.9)
|
57 (40.7)
|
Rf
|
|
|
|
Male
|
1201 (68.3)
|
1118 (69.1)
|
83 (59.3)
|
0.653 (0.458-0.929)
|
0.018
|
|
|
Age group, years
|
|
|
|
|
|
|
|
<30
|
873 (49.6)
|
822 (50.8)
|
51 (36.5)
|
Rf
|
|
|
|
30~49
|
536 (30.5)
|
500 (30.9)
|
36 (25.7)
|
1.160 (0.747-1.803)
|
0.508
|
|
|
50~69
|
290 (16.5)
|
247 (15.2)
|
43 (30.7)
|
2.806 (1.825-4.313)
|
<0.001
|
|
|
≥70
|
60 (3.4)
|
50 (3.1)
|
10 (7.1)
|
3.224 (1.545-6.726)
|
0.002
|
|
|
Residence years in SZ
|
|
|
|
|
|
|
|
(0,1]
|
513 (32.5)
|
488 (33.5)
|
25 (20.9)
|
Rf
|
|
|
|
(1,2]
|
177 (11.2)
|
164 (11.2)
|
13 (10.8)
|
1.547 (0.774-3.095)
|
0.217
|
2.785 (0.937-8.280)
|
0.065
|
(2,+∞)
|
889 (56.3)
|
807 (55.3)
|
82 (68.3)
|
1.983 (1.250-3.147)
|
0.004
|
4.205 (1.851-9.552)
|
0.001
|
Occupation
|
|
|
|
|
|
|
|
Active
|
1048 (59.6)
|
978 (60.4)
|
70 (50.0)
|
Rf
|
|
|
|
Students
|
88 (5.0)
|
79 (4.9)
|
9 (6.4)
|
1.592 (0.766-3.306)
|
0.213
|
|
|
Retired or Unemployed
|
623 (35.4)
|
562 (34.7)
|
61 (43.6)
|
1.516 (1.059-2.171)
|
0.023
|
|
|
Annual income, yuan
|
|
|
|
|
|
|
|
<30000
|
309 (35.0)
|
288 (35.5)
|
21 (29.2)
|
Rf
|
|
|
|
30000~50000
|
212 (24.0)
|
196 (24.2)
|
16 (22.2)
|
1.120 (0.570-2.199)
|
0.743
|
|
|
50000~80000
|
163 (18.5)
|
144 (17.7)
|
19 (26.4)
|
1.810 (0.943-3.473)
|
0.075
|
|
|
>80000
|
199 (22.5)
|
183 (22.6)
|
16 (22.2)
|
1.199 (0.610-2.358)
|
0.599
|
|
|
Clinical factors (yes v no)
|
|
|
|
|
|
|
|
TB history
|
91 (5.2)
|
72 (4.4)
|
19 (13.6)
|
3.374 (1.969-5.780)
|
<0.001
|
4.263 (1.871-9.714)
|
0.001
|
Hypertension
|
24 (1.4)
|
22 (1.4)
|
2 (1.4)
|
1.052 (0.245-4.521)
|
0.946
|
|
|
Diabetes mellitus
|
62 (3.5)
|
57 (3.5)
|
5 (3.6)
|
1.015 (0.400-2.575)
|
0.975
|
|
|
Pulmonary cavity
|
427 (24.3)
|
399 (24.6)
|
28 (20.0)
|
0.764 (0.498-1.174)
|
0.220
|
|
|
Clinical symptoms (yes v no)
|
|
|
|
|
|
|
|
Cough
|
791 (45.0)
|
738 (45.6)
|
53 (37.9)
|
0.727 (0.510-1.037)
|
0.079
|
0.548 (0.310-0.970)
|
0.039
|
Hemoptysis
|
169 (9.6)
|
159 (9.8)
|
10 (7.1)
|
0.706 (0.364-1.372)
|
0.305
|
|
|
Chest Pain
|
113 (6.4)
|
106 (6.5)
|
7 (5.0)
|
0.751 (0.343-1.647)
|
0.475
|
|
|
Fever
|
72 (4.1)
|
65 (4.0)
|
7 (5.0)
|
1.258 (0.566-2.799)
|
0.573
|
|
|
Others
|
46 (2.6)
|
44 (2.7)
|
2 (1.4)
|
0.519 (0.124-2.163)
|
0.368
|
|
|
MTBC: Mycobacterium tuberculosis complex; NTM: Nontuberculous mycobacteria; SZ: Shenzhen; OR: Odds Ratio; CI: Confidence Interval. |
Consistency of the Kraken 2 / Bracken and Hain method
Of the 1759 total, 1032 were also analyzed by the Hain test for mycobacterial species. 1030 of 1032 isolates were identified by Hain as NTM or MTBC, while 2/1032 were found to be co-infections with NTM and MTBC. The agreement between the Kraken 2 / Bracken method and the Hain test (MTBC (n=931), NTM (n=74)) was 97.57% (1005/1030) with a kappa value of 0.842 (P < 0.001). Among the 74 isolates identified as NTM by both methods (Table 3), the Kraken 2 / Bracken method identified 33 as M. abscessus, of which 29/33 (87.88%) were also identified as M. abscessus using Hain, 2/33 were identified as M. gordonae, 1/33 as a mixed infection of M. gordonae and M. abscessus and 1/33 as an unidentified species. For the 5 strains designated as M. fortuitum by Kraken 2 / Bracken, 3/5 (60%) were identified as M. fortuitum by Hain, and 2/5 were unidentified species. The species designations by Kraken 2 / Bracken and Hain were identical for M. avium (8/8), M. kansasii (8/8) and M. intracellulare (7/7) isolates.
Table 3
Comparison between Kraken 2 / Bracken and Hain for 74 strains isolated as NTM
Kraken 2 / Bracken
|
Hain
|
Consistency
|
33/74 M. abscessus
|
29/33 M. abscessus
|
29/33, 87.88%
|
|
1/33 M. gordonae
|
|
|
1/33 M. gordonae/M. abscessus
|
|
|
1/33 M. chelonae
|
|
|
1/33 Unidentified species
|
|
8/74 M. avium
|
8/8 M. avium
|
8/8, 100%
|
8/74 M. kansasii
|
8/8 M. kansasii
|
8/8, 100%
|
8/74 M. sp. VKM Ac-1817D
|
8/8 M. fortuitum
|
0%
|
7/74 M. intracellulare
|
7/7 M. intracellulare
|
7/7, 100%
|
5/74 M. fortuitum
|
3/5 M. fortuitum
|
3/5, 60%
|
|
2/5 Unidentified species
|
|
2/74 M. colombiense
|
2/2 M. intracellulare
|
0%
|
2/74 M. marseillense
|
2/2 M. intracellulare
|
0%
|
1/74 M. chimaera
|
1/1 M. malmoense/M. avium
|
0%
|
Total (n=74)
|
Total (n=74)
|
55/74, 74.32%
|
NTM: Nontuberculous mycobacteria. |
Discrepancies between Hain and Kraken 2 / Bracken
The Hain test on the sputum cultures of eight patients found NTMs (2 M. fortuitum, 1 M. kansasii, 2 M. abscessus and 3 unidentified species), while Kraken 2 / Bracken analysis of the WGS of these 8 cultures found MTBC (Supplementary Table S2). Although the sputum smears were negative for seven of these eight patients, all were treated for tuberculosis based on clinical judgement. The WGS analysis was performed retrospectively, much later and did not influence therapy. Seven completed their treatment successfully and the eighth, after 4 months of the standard TB regimen, was transferred for NTM treatment. For this eighth patient, M. abscessus was diagnosed in their sputum by the Hain test and only 59% of WGS reads from their sputum culture mapped to MTBC.
In another seventeen patients, Hain found MTBC in the sputum cultures while Kraken 2 / Bracken found NTM in their WGS: 6 M. abscessus (> 95% reads); 3 M. kansasii (85%, 98% and 99% reads); 1 M. colombiense (96% reads); 1 M. intracellulare (58% reads); 1 M. fortuitum (47% reads); 1 M chimaera (41% reads); 3 M. sp. VKM Ac-1817D (38%, 48% and 50% reads); and 1 M. sp YC-RL4 (21% reads). Of these, 12/17 completed treatment for TB and 3 were lost to follow-up, perhaps because they went to their hometowns to be treated. 2 patients were transferred for MDR-TB treatment after a month or two on the standard drug sensitive TB regimen. In the sputa of two patients, Hain found mixed infections of M. abscessus and MTBC, and M. gordonae and MTBC, while Kraken 2 / Bracken found M. abscessus (99% of reads) and MTBC (67% of reads), respectively. The patient with M. abscessus and MTBC, who had a cough > 2 weeks, a 2+ positive sputum and a prior history of TB, received 8 months of TB treatment (2HRZES3/6HRE) and was cured. The patient with M. gordonae and MTBC, who had no symptoms, a negative sputum and no prior history of TB, completed standard TB therapy (2HRZE/4HR).
MAC diversity revealed by WGS
Taxonomic classification of WGS data from the MAC isolates (M. avium, M. intracellulare, M. colombiense, M. marseillense, M. chimaera and M. paraintracellulare) was performed using Kraken 2 followed by Bayesian re-estimation of relative abundances using Bracken (Fig. 2). The 41 samples belonging to the MAC were clustered by their Bray-Curtis dissimilarity distances into two major groups: one predominantly M. avium; and a second, mixed group mainly comprised of M. intracellulare, M. colombiense and M. marseillense. The isolates in the M. avium cluster had reads that mapped almost exclusively to M. avium (༞96%), whereas the reads from isolates within the mixed group mapped to different MAC species: in the M. intracellulare cluster, the percentage of reads classified as M. intracellulare ranged from 31–84%; in the M. marseillense cluster, 34%-96% of reads were classified as M. marseillense; in the M. chimaera cluster, 24%-88% were classified as M. chimaera; and in the M. colombiense cluster 78%-96% of reads were classified as M. colombiense (Supplementary Table S3).