The 2020 Global Tuberculosis Report6 produced by the World Health Organization (WHO) includes reported resistance patterns in 198 countries and territories accounting for more than 99% of estimated global TB cases. The WHO, together with other international guidelines, groups RMP-resistant TB with MDR-TB because mono-resistant TB that is resistant to RMP requires similar treatment as MDR-TB. (Thus, all further reference to MDR-TB can be read as including RMP-resistant TB.) The global mean of MDR-TB has remained at 3-4% of all new cases, and 14-18% of previously treated cases. In 2019, an estimated 465,000 cases of MDR-TB emerged globally, with India, China and the Russian Federation accounting for almost 50% of the world’s total cases. In addition, 20.1% of these were found to have pre-XDR-TB.
The most recent report from the WHO indicated the population-weighted mean of resistance to any of INH, RMP, EMB or streptomycin was 17.0% (95% CI 13.6 to 20.4%) in new cases, 35.0% (CI 24.1 to 45.8%) in previously treated cases and 20% (CI 16.1 to 23.9%) in all TB cases.6
The overall pattern of TB drug resistance in Canada from 2011-2015 is shown in Table 1.7 In 2018, the most recent year reported, 10.1% of 1,459 M. tuberculosis isolates in Canada were resistant to one or more drugs. The majority were mono-resistant (81.8%, n = 121), with INH, PZA and RMP mono-resistance at 60.1% (n = 89), 17.6% (n = 26) and 4% (n = 6), respectively.7 Poly-resistance was found only in 5 isolates; which were all resistant to both INH and PZA. MDR-TB was found in 1.4% (n = 21), with both fluoroquinolone and second-line injectable resistance in one isolate. Most TB cases (69.5%) and most MDR-TB cases (78.4%) in Canada were reported from 3 provinces: BC, Ontario and Quebec.7 While prevalence of drug resistance stratified by prior TB treatment status has not been reported in recent years, between 2006 and 2010, drugresistant TB was reported most commonly in people with a past history of TB (“re-treatment cases,” previously called “relapse” cases). About 83% of drug-resistant TB from 2006-2016 were reported in the foreign-born population.7
Table 1. Drug resistance on initial and follow-up isolates of M. tuberculosis complex, in Canada, 2011-2015. 7
|All isolates (Total)||6,819||100.00|
|Fully susceptible isolate to first-line drugs||6,159||90.32|
|Any resistance to INH||543||7.96|
|Any resistance to RMP||96||1.41|
|Any resistance to EMB||39||0.57|
|Any resistance to PZA||155||2.27|
|Resistant to ≥1 first line drug||660||9.68|
|MDR with FQN-R and SLI-R||4||0.06|
Abbreviations: INH, isoniazid; RMP, rifampin; EMB, ethambutol; PZA, pyrazinamide; MDR, multidrug-resistant; FQN-R, fluoroquinolone-resistant; SLI-R, second line injectable-resistant.
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