Mycobacterium tuberculosis

Introduction

Of all infectious diseases, tuberculosis (TB) has the highest mortality worldwide. Although the incidence is slowly declining, it has been estimated that about one third of the global population is latently infected by its causative agent; Mycobacterium tuberculosis. In the Netherlands we have reached the elimination phase. Not less than 75% of the TB cases is currently diagnosed in foreign-borns.

Because of the increased influx of asylum seekers and immigrants, in 2016 there was an increase of about 3% in the notification of TB (889 cases). In 2017, the number of TB cases declined to 794 cases.

Worldwide, there is a concern on the development of resistance, which hampers adequate treatment of tuberculosis. The majority of resistance testing of M. tuberculosis isolates in the Netherlands is performed at the RIVM and the results are used both for direct therapy guidance and surveillance.

If resistance is diagnosed in other laboratories, this is verified at the TB reference laboratory at the RIVM. The RIVM participates in the resistance proficiency study of the WHO for WHO supra-national laboratories to monitor the quality of the resistance testing.

Around 35 laboratories in the Netherlands involved in the diagnosis of TB send all M. tuberculosis isolates to the RIVM for epidemiological typing to support the investigations on TB transmission by Municipal Health Services.

Methods

The current gold standard in drug susceptibility testing (DST) is the WHO recommended mycobacteria growth indicator tube (MGIT) system. In this approach bacteria are incubated in the presence of critical concentrations of drugs. The MGIT incubator automatically monitors the growth of the bacteria.

Since 2011, not all drug susceptibility testing for first line drugs is performed at the RIVM; a part of these tests is performed at regional or peripheral laboratories. When resistance is observed, however, this is reported to the national reference laboratory at the RIVM for verification and/or additional resistance testing. The results on the 25% of cultures for which DST has been performed outside of the RIVM have been collected for the year 2016 and this confirmed this recommendation is followed consistently.

Results

The presented data on 2017 is preliminary, as not all data is currently available. The in vitro generation time of M. tuberculosis is long and it takes several weeks before cultures become positive, are sent to the RIVM, and the drug susceptibility testing has been finalized.

In the year 2017, 534 M. tuberculosis complex isolates were received at the RIVM for epidemiological typing, of which 329 (62%) were subjected to DST for first line drugs at the RIVM.

In 2017, the number of TB notification cases was 794, of which 534 M. tuberculosis complex isolates were received at the RIVM for epidemiological typing.

Until 2010, the rate of INH resistance increased to 9.0%, but since 2011 it decreased over the years to 5.4 % in 2015. In 2016 there was a clear increase in INH resistance to 7.1% (figure 4.6.3.1), but this slightly decreased to 6.7% in 2017. Rifampicin resistance decreased from 3.1% in 2013 to 1.3% in 2014. In 2015 and 2016 the rifampicin resistance increased marginally from to 1.9% to 2.6%. In 2017 rifampicin resistance decreased again to 2.1% of the cases. In 2017, in 0.9% of the cases ethambutol resistance was detected.

Figure 4.6.3.1 Trends in antibiotic resistance for M. tuberculosis 2002-2017.

Figure 4.6.3.2 Trends in combined antibiotic resistance for M. tuberculosis 2002-2017.

INH

rifampicin ethambutol streptomycin

Percentage

’02 ’03 ’04 ’05 ’06 ’07 ’08 ’09 ’10 ’11 ’12 ’13 ’14 ’15 ’16 ’17 0%

2%

4%

6%

8%

10%

’02 ’03 ’04 ’05 ’06 ’07 ’08 ’09 ’10 ’11 ’12 ’13 ’14 ’15’16’17

streptomycin

Percentage

streptomycin + ethambutol ethambutol

rifampicin + ethambutol rifampicin + streptomycin rifampicin

INH + ethambutol

INH + streptomycin + ethambutol INH + streptomycin

INH + rifampicin + ethambutol INH + rifampicin + streptomycin + ethambutol

INH + rifampicin + streptomycin INH + rifampicin

0% INH 2%

4%

6%

8%

10%

12%

14%

16%

Multidrug resistant tuberculosis (MDR-TB), defined as resistance to at least INH and rifampicin, was found in 1.1% of the isolates in 2014 and 1.8 % of the isolates in 2015 (figure 4.6.3.2). In 2016, 2.1% of the isolates were reported as MDR-TB. In 2017, 10 MDR-TB cases were diagnosed (1.3%). XDR-TB was not diagnosed in 2017. In recent years mono-resistance to rifampicin was incidentally found; in 2016 in 2 cases and in 2017 one case.

Discussion

Worldwide, resistance is an important aspect of TB control. Because there was a slight increase in the notification of TB in the Netherlands in the period 2015-2016, due to a higher influx of asylum seekers and immigrants from high prevalence areas, it remains important to continue the surveillance on resistance. In 2017 the notification of TB declined with 11% mainly due to a reduced number of newly arrived residents.

In 2017, 10.6% percent of the 534 isolates tested in the Netherlands revealed some form of resistance.

Although the number of multidrug resistant isolates remained low and amounted to 10 cases, due to the extended hospitalization of patients and the cumbersome treatment this problem deserves special attention.

In 2016, a new project was initiated at the RIVM on structural Whole Genome Sequencing (WGS) of M. tuberculosis isolates. It is being investigated whether the detection of mutations in 23 resistance genes is a reliable predictor of resistance. In the period 2018/2019 WGS will be increasingly used to screen for resistance in M. tuberculosis isolates.

Conclusions

• Resistance to the antibiotics to treat tuberculosis remained almost stable over the last 5 years, and only slightly increased in 2017.

• MDR-TB remained stable in the recent years, and decreased to 1.3% in 2017.

• Tuberculosis notification increased with 6% in 2015 and 3% in 2016, but decreased with 11% in 2017.

References

Evaluation of Mycobacteria Growth Indicator Tube (MGIT) for drug susceptibility testing for Mycobacterium tuberculosis. J.C. Palomino, H. Traore, K. Fissette, F. Portaels; Int J. Tuberc Lung Dis 1999 3(4);344-348.

Drug Susceptibility Testing of Mycobacterium tuberculosis Complex by Use of a High-Throughput, Reproducible, AbsoluteConcentration Method. Bert van Klingeren, Mirjam Dessens-Kroon, Tridia van der Laan, Kristin Kremer, and Dick van Soolingena

JOURNAL OF CLINICAL MICROBIOLOGY, Aug. 2007, p. 2662-2668.

Whole-genome sequencing for prediction of Mycobacterium tuberculosis drug susceptibility and resistance:

a retrospective cohort study. Walker1, Kohl TA2, Omar SV3, Hedge J4, Del Ojo Elias C4, Bradley P5, Iqbal Z5,

Feuerriegel S6, Niehaus KE7, Wilson DJ4, Clifton DA7, Kapatai G8, Ip CL5, Bowden R5, Drobniewski FA⁹, Allix-Béguec C¹⁰, Gaudin C¹⁰, Parkhill J11, Diel R¹², Supply P¹³, Crook DW¹⁴, Smith EG¹⁵, Walker AS¹⁴, Ismail N¹⁶, Niemann S6, Peto TE¹⁴; Lancet Infect Dis. 2015 Oct;15(10):1193-202.