Tuberculosis: Drug resistance in Canada, 1999

Reported susceptibility results of the Canadian Tuberculosis Laboratory Surveillance System

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TABLE OF CONTENTS

INTRODUCTION
METHODOLOGY
RESULTS
DISCUSSION
FIGURES
Figure 1.	Reported TB drug resistance in Canada by province/territory - 1999
Figure 2.	Reported MTB isolates in Canada by province/territory - 1999
Figure 3.	Overall pattern of reported TB drug resistance in Canada - 1999
Figure 4.	Reported TB drug resistance in Canada by type of drug - 1999
Figure 5.	Reported TB drug resistance in Canada by sex and year of birth - 1999
TABLES
Table A.	Concentrations for routine testing of first-line anti-tuberculosis drugs
Table 1.	Overall pattern of reported TB drug resistance in Canada - 1998-1999
Table 2.	Reported MTB isolates by "reporting" and "originating" province/territory,  Canada - 1999
Table 3.	Reported MDR-TB isolates by province/territory, Canada - 1999
Table 4.	Reported TB drug resistance by sex and year of birth, Canada - 1999
Table 5.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Alberta - 1998-1999
Table 6.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, British Columbia - 1998-1999
Table 7.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Manitoba - 1998-1999
Table 8.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, New Brunswick - 1998-1999
Table 9.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Newfoundland - 1998-1999
Table 10.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Northwest Territories - 1998-1999
Table 11.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Nova Scotia - 1998-1999
Table 12.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Nunavut - 1998-1999
Table 13.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Ontario - 1998-1999
Table 14.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Prince Edward Island - 1998-1999
Table 15.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Québec - 1998-1999
Table 16.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Saskatchewan - 1998-1999
Table 17.	Reported results for routine drug susceptibility testing of MTB isolates to first-line anti-tuberculosis drugs, Yukon Territory - 1998-1999
LIMITATIONS
CONCLUSIONS
REFERENCE
APPENDICES
Appendix 1 -	Participating Laboratories of the Canadian Tuberculosis Laboratory Surveillance System (CTBLSS)
Appendix 2 -	M. tuberculosis Complex Antimicrobial Susceptibility Reporting Form

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INTRODUCTION

Tuberculosis Prevention and Control at the Centre for Infectious Disease Prevention and Control, Health Canada, in collaboration with the Canadian Tuberculosis Laboratory Technical Network and participating laboratories (representing all provinces and territories) in the Canadian Tuberculosis Laboratory Surveillance System (CTBLSS) (Appendix 1), established a laboratory-based national surveillance system in 1998 to monitor tuberculosis (TB) drug resistance patterns in Canada.

Laboratories report their results on anti-tuberculosis drug susceptibility testing to Tuberculosis Prevention and Control for every patient for whom a specimen or an isolate has been received for each calendar year. Tuberculosis Prevention and Control subsequently conduct analyses to produce an annual report. This report presents 1999 and adjusted 1998 (to reflect late reporting) drug susceptibility data for TB isolates across Canada as of April 10, 2000.

METHODOLOGY

A computerized database containing drug susceptibility test results of Mycobacterium tuberculosis (MTB) and MTB complex (MTBC) isolates is maintained at Tuberculosis Prevention and Control at the Centre for Infectious Disease Prevention and Control. Data are collected either through manual completion and mailing of a standard reporting form (Appendix 2) or by electronic transmission. Information collected includes sex, year of birth, province/territory from which the report originates, province/territory from which the specimen originates and susceptibility results. Every effort is made to eliminate duplicate specimens; only the most recent susceptibility results for a given patient in the current reporting year are included for analysis.

Manitoba, Ontario and Newfoundland identify the species and test all isolates for drug resistance in their respective provinces. Some provinces identify the species and test their own isolates and those of other provinces/territories (British Columbia: British Columbia and Yukon Territory isolates; Alberta: Alberta, Northwest Territories and some Nunavut isolates; Quebec: Quebec, New Brunswick, Northwest Territories and Nunavut isolates; Nova Scotia: Nova Scotia and Prince Edward Island isolates). Saskatchewan tests for drug resistance on all MTBC isolates; other provinces and territories report results at the species level, excluding M. bovis BCG.

Routine susceptibility testing of MTB or MTBC to first-line anti-tuberculosis drugs is generally performed using the radiometric proportion method (Bactec^®). Table A lists the first-line anti-tuberculosis drugs and the concentrations in mg/L used by the participating laboratories. Results of susceptibility testing for second-line anti-tuberculosis drugs are not included in this report.

As noted in Table A, the number and specific first-line anti-tuberculosis drugs for which routine susceptibility testing is carried out differ among the provinces and territories. Accordingly, the number of isolates included in the descriptive analyses that were carried out vary. Analyses were performed using SAS 6.12.

RESULTS

In 1999, participating laboratories across Canada reported drug susceptibility results for 1,434 isolates of MTBC. Twenty-three M. bovis isolates were reported: 20 isolates of M. bovis BCG and 3 isolates of M. bovis other than BCG. Only the 3 (0.2%) M. bovis other than BCG isolates (one each from Quebec, Ontario and British Columbia) are included in the analyses, leaving a total of 1,414 isolates. The majority of isolates originated from Ontario, Quebec, British Columbia, Alberta and Manitoba. The Yukon Territory reported no isolates for 1999.

Of the 1,414 isolates in 1999 included for analysis, 173 (12.2%) were resistant to one or more first-line anti-tuberculosis drug(s). Resistance to INH was the most common type of drug resistance (8.9%). A total of 17 isolates (1.2%) were multi-drug resistant tuberculosis (MDR-TB) strains (defined as resistance to at least INH and RMP); of which eight isolates demonstrated resistance to four or five first-line anti-tuberculosis drugs tested. These isolates were reported from Ontario, Quebec, Manitoba and British Columbia. In addition, Alberta and Saskatchewan reported isolates with other patterns of multi-resistance. Nova Scotia's one reported drug resistant isolate was resistant to INH only. Five provinces and territories (Nunavut, Northwest Territories, Newfoundland, Prince Edward Island and New Brunswick) reported that all their isolates were susceptibile to all the first-line anti-tuberculosis drugs that were tested.

Demographic information on the individual patients from whom the isolates originated was limited in this laboratory-based surveillance system. Of the 1,281 isolates for which the year of birth was known, 57% reported a year of birth between 1941 and 1980. Among the 141 drug resistant isolates for which year of birth was known, 69% reported a year of birth between 1941 and 1980. Males accounted for 56% of all the isolates and 65% of the drug resistant isolates for which sex was reported.

Table A: Concentrations for routine testing of first-line anti-tuberculosis drugs
Anti-tuberculosis drugs	mg/L	Comments
Isoniazid (INH)	0.1
Rifampin (RMP)	2.0
Ethambutol (EMB)	2.5	British Columbia uses a concentration of 4.0 mg/L.
Streptomycin (SM)	2.0	Routine testing is not performed for isolates from Quebec, Nova Scotia, New Brunswick, Prince Edward Island and for Nunavut isolates tested in Quebec.
Pyrazinamide (PZA)	100.0	Routine testing is not performed for isolates from British Columbia, Saskatchewan and the Yukon Territory.

DISCUSSION

The number of reported TB isolates in 1999 decreased by 3.4% from the previous year (1,464 to 1,414 isolates). While the percentage of isolates demonstrating any type of drug resistance increased from 11.9% in 1998 to 12.2% in 1999, the proportion of isolates classified as MDR-TB was identical for both years (1.2%). Quebec accounted for most of the rise in INH monoresistance; however, routine testing for SM was stopped in this province in January of 1999. Therefore, results previously classified as resistance to INH+SM would now be recorded as INH monoresistance and may account for this increase.

Over 90% of the reported laboratory TB isolates in Canada in 1999 originated from five provinces. The two largest provinces (Ontario and Quebec) consistently reported the majority of isolates and MDR-TB in the two years of data collection. Since the initiation of this laboratory-based surveillance system that began January 1, 1998, Saskatchewan, the Atlantic Provinces and the Territories have not reported any MDR-TB cases.

The results observed to date in this surveillance system are consistent with international data. In the latest report of the global TB drug resistance surveillance project jointly conducted by the World Health Organization (WHO) and the International Union Against Tuberculosis and Lung Disease (IUATLD), the median prevalence of overall TB drug resistance among the participating countries was 11.1% (as compared to 12.2% for Canada) and the median prevalence of MDR-TB was 1.7%¹ (as compared to 1.2% for Canada).

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Figure 1
Reported TB drug resistance in Canada by province/territory - 1999 (n = 1,414)

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Figure 2
Reported MTB isolates in Canada by province/territory - 1999 (n = 1,414)

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Figure 3
Overall pattern of reported TB drug resistance in Canada - 1999 (n = 171)

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Figure 4
Reported TB drug resistance in Canada by type of drug - 1999 (n = 171)

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Figure 5
Reported TB drug resistance in Canada by sex and year of birth - 1999 (n = 171)

 

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HOW TO REACH US

For more information, copies of this report or other reports, please contact:

Tuberculosis Prevention and Control
Centre for Infectious Disease Prevention and Control
Public Health Agency of Canada
Health Canada
Room 0108 B, Brooke Claxton Building
Tunney's Pasture, Ottawa, Ontario K1A 0K9

Internal Postal Address: 0900B-1

Telephone: (613) 941-0238
Facsimile: (613) 946-3902

The following text, figures and tables were prepared by:

Penny Nault
Tuberculosis Database Manager
Tuberculosis Prevention and Control

Melissa Phypers, MSc
A/Chief
Tuberculosis Prevention and Control

ACKNOWLEDGEMENT

Tuberculosis Prevention and Control would like to acknowledge the members of the Canadian Tuberculosis Laboratory Technical Network and their teams for their contribution to and their participation in the Canadian Tuberculosis Laboratory Surveillance System (CTBLSS).

Published by authority of the Minister of Health

© Her Majesty the Queen in Right of Canada, represented by the Minister of Public Works and Government Services Canada, 2002.

Cat. H49-110/2001
ISBN 0-662-66495-7

This publication can be made available in alternative formats.