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Prevalences of levofloxacin resistance and pncA mutation in isoniazid-resistant Mycobacterium tuberculosis in Hong Kong.

INTRODUCTION
In 2018, the World Health Organization recommended a 6-month treatment regimen that included levofloxacin and pyrazinamide for isoniazid-resistant Mycobacterium tuberculosis without rifampicin resistance (Hr-TB). Susceptibility testing for both drugs is not routinely performed for Hr-TB in Hong Kong. This study examined the prevalences of levofloxacin and pyrazinamide resistances in Hr-TB and explored associated risk factors.


METHODS
All Hr-TB isolates archived during 2018 were retrieved. Isolates were de-duplicated to identify unique cases. Levofloxacin susceptibility testing was performed using the MGIT 960 System; pncA gene sequencing was used as a surrogate indicator of pyrazinamide susceptibility. Previous laboratory records for each case were analysed.


RESULTS
In total, 160 phenotypic Hr-TB cases were identified from among 3411 patients with tuberculosis (4.7%). Among these, 157 were analysed, revealing 0.6% (n=1) levofloxacin resistance and 4.5% (n=7) pyrazinamide resistance, respectively. Independent risk factors associated with pncA mutations included history of tuberculosis in the affected patient and isoniazid poly-resistance (ie, double and triple resistances), but not mono-resistance.


CONCLUSION
For Hr-TB in Hong Kong, levofloxacin resistance is rare and pyrazinamide resistance-associated pncA mutations are uncommon. Routine susceptibility testing for these drugs is not indicated unless related risk factors are identified.