Epidemiology & BackgroundMDR-TB remained stable over the same time period. Overall, drug-resistant...

1Epidemiology & BackgroundDefinitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Drug-resistant TB across the globe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Drug-resistant TB in the United States . . . . . . . . . . . . . . . . . . . . . . . . . 3

Sources of drug-resistant TB in the United States . . . . . . . . . . . . . . . 7

How is drug resistance generated? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3rd edition contributors: JENNIFER M. FLOOD, MD, MPH & LISA PASCOPELLA, PhD, MPH

DRUG-RESISTANT TUBERCULOSIS : 1 : A SURVIVAL GUIDE FOR CLINICIANS : 3RD EDITION

Efforts to control TB throughout the world have been challenged in recent decades by the emergence of drug-resistant TB.

Drug-resistant tuberculosis (TB) is a deadly communicable disease that poses a serious

global health threat. It impacts not only individual patients and their families, but also

imposes tremendous burdens on overextended public health systems that may lack the

resources needed to contain it.

DEFINITIONS

• Multidrug-resistant (MDR) refers to TB caused by

Mycobacterium tuberculosis (M. tuberculosis) that is resistant to at least isoniazid (INH) and rifampin (RIF).

• Pre-extensively drug-resistant (Pre-XDR) refers to

MDR-TB that is also resistant to either a fluoroquinolone or a second-line injectable anti-TB drug (kanamycin, capreomycin, or amikacin), but not both.

• Extensively drug-resistant (XDR) refers to MDR-TB that

is also resistant to both a fluoroquinolone and a second-line injectable anti-TB drug.

Drug-resistant TB across the globeIn 2014, an estimated 480,000 people developed MDR-TB and 190,000 people died from MDR-TB. By 2015, 105 countries had reported at least one case of XDR-TB. An estimated 21% of MDR-TB cases worldwide have additional resistance to a fluoroquinolone, and 9.7% have XDR-TB. According to the World Health Organization

(WHO), more than half of the global burden of MDR-TB is currently in three countries:

India, China, and the Russian Federation.

Worldwide and in most countries with a high burden of MDR-TB, WHO estimates that in 2014 only 41% of those with MDR-TB were actually diagnosed by laboratory testing.

Fortunately, there are new and vigorous efforts for control of TB and for early diagnosis

and treatment of drug-susceptible and drug-resistant TB worldwide. Large-scale imple-

mentation of rapid molecular tests for early detection of both the presence of TB and, at

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a minimum, rifamycin resistance has occurred in many high-burden countries. The

Patients’ Charter for Tuberculosis Care, developed by the World Care Council, promotes

a “patient-centered” approach to tuberculosis care. The updated International Standards

for Tuberculosis Care (ISTC) presents a set of widely accepted, evidence-based stan-

dards describing a level of care that all practitioners, public and private, should seek to

achieve in managing patients with, or suspected of having, TB.

WHO reported improvements in detection and treatment of MDR-TB in 2014: 111,000

people with MDR-TB were started on second-line treatment, equivalent to 90% of the

123,000 newly-detected cases that were reported and eligible for treatment globally.

However, treatment coverage gaps for detected cases were much larger in some countries, notably the high-burden countries of China (49%), Myanmar (44%), and Nige-

ria (53%).

Finally, improvements in early identification and enrollment into treatment must also be

followed by quality of care measures that ensure treatment success. Only three high-bur-

den countries reported a treatment success rate for MDR-TB of 75% or higher. On aver-age, only 50% of MDR-TB patients in the 2012 cohort of detected cases were treated successfully. Many countries lack the resources needed to provide sufficient

quality of care. These disparities must be addressed to prevent further transmission of

disease and more extensive resistance.

In many high-burden countries, a standardized MDR-TB regimen is used due to the lack

of routine access to second-line drug-susceptibility testing (DST). The success or failure

of treatment of these cases overseas can impact the presentation of drug resistance in

the United States (U.S.) through immigration. It is important for U.S. clinicians to under-

stand the diversity of global practices.

A milestone for improved MDR-TB care occurred in 2012 when bedaquiline (BDQ) fumarate (Sirturo, Janssen) became the first TB drug in a novel class to be approved in

40 years. In October 2013, the U.S. Centers for Disease Control and Prevention (CDC)

issued provisional guidance for its use in the treatment of MDR-TB. A second new drug,

delamanid (Deltyba, Otsuka), also gained provisional approval for use in the European

Union in 2014, and additional drugs are in the development pipeline.

Drug-resistant TB in the United States In the United States in 2010-2013:

• 413 TB patients had MDR-TB based on initial DST. Of these, 49 patients had pre-XDR-TB, and 12 patients had XDR-TB. In other words, 15% of U.S. MDR-TB patients had pre-XDR or XDR.

• Thirty-eight states plus the District of Columbia reported at least 1 MDR-TB case;19 states reported at least 1 pre-XDR-TB case; and 8 states reported at least 1XDR-TB case. See Figure 1.

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Although the number of drug-resistant cases of TB in the United States declined as the

number of total reported TB cases decreased, there has been little change in the per-

centage (1.0–1.6%) of TB patients with MDR-TB during 2000-2013. On the other hand,

the percentage of patients with INH resistance has increased from 7.9% in 2000 to 9.2%

in 2013. The increase in INH-resistant TB is troubling because it is one mutation away

from becoming MDR-TB.

In recent years, the percentage of patients with pyrazinamide (PZA)-resistant TB has also

increased (from 2.0% to 3.3% during 1999-2009). TB patients with PZA resistance include

those with TB infections caused by M. bovis (a member of the M. tuberculosis complex

that is intrinsically resistant to PZA) and M. tuberculosis. M. bovis accounted for an aver-

age of 1.7% of culture proven cases from 2008-2013.

In the United States, drug resistance in foreign-born persons with TB is much more com-

mon than in U.S.-born persons with TB, corresponding to the higher rates of drug resis-

tance in the countries of origin.

• In 2013, 90% of MDR-TB cases in the United States were among foreign-bornpersons.

• Among foreign-born patients who arrived in the United States within 2 years ofTB diagnosis (recent arrivers), 3.2% had MDR-TB, compared to 1.4% of thosediagnosed with TB more than 2 years after they arrived (remote arrivers).

FIGURE 1.

Drug-resistant TB in United States, 2010-2013

41,195 TB cases reported

31,519 (77%) TB cases with positive cultures

30,978 (98%) TB cases with positive cultures and DST done

2,794 (9%) INH-resistant TB cases

49 (12%) pre-XDR TB cases

12 (3%) XDR TB cases

413 (1.3%) MDR TB cases

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Figure 2 shows that the percentage of U.S.-born TB patients with INH resistance increased

from 4.5% to 5.8% from 2000 to 2013. Among foreign-born TB patients over the same

time period, the percentage of INH-resistant TB remained the same, at about 11% in both

recent and remote arrivers.

The small percentage of U.S.-born TB patients with

MDR-TB slightly declined from 2000 (0.6%, N=42) to

2013 (0.4%, N=9), while the percentage of foreign-born

recent (3%, N=33) and remote (1.4%, N=47) arrivers with

MDR-TB remained stable over the same time period.

Overall, drug-resistant TB is also more common among

TB patients who were born in countries with an estimated

high prevalence of drug resistance. Discordance between

WHO and U.S. estimates of MDR-TB by country-of-origin

was documented in a recent study that demonstrated that

the U.S. National TB Surveillance system (NTSS) better

predicted the prevalence of drug resistance in foreign-

born U.S. residents with TB than the WHO/International Union Against Tuberculosis and

Lung Diseases (IUATLD) Global Project on Anti-Tuberculosis Drug Resistance Surveil-

lance (Global DRS). Of the 413 foreign-born patients diagnosed with MDR-TB in the

United States from 2010 to 2013, 75% were born in only 15 countries. Table 1 shows the

drug resistance pattern for the top 15 countries of origin for cases of drug-resistant TB in

the United States.

| | | | | | | | | | | | | |

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

300

250

200

150

100

50

0

Cases per year Percent of all U.S.-born cases INH resistant

FIGURE 2.

U.S.-born INH resistant TB cases and percentages, 2000-2013

139150

182181201203

182185210

230232232

273294

4.5% 4.6%4.3% 4.5% 4.6% 4.5%

4.2%

5.2%

4.4%

6.1%5.8%

6.3%

5.6% 5.8%

INH-resistant TB among

U.S.-born patients slightly

increased from 2000-2013.

Rates of INH-resistant and

MDR-TB among all groups

have otherwise remained

stable during this period.

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TABLE 1.

Drug resistance among foreign-born TB patients in the United States, 2010-2013 (Top 15 countries)

Country of originTotal TB cases*

MDR Any resistance** INH resistance

No. % No. % No. %

India 2,122 40 1.9 258 12.2 166 7.8

Philippines 3,068 39 1.3 484 15.8 386 12.6

Mexico 5,542 37 0.7 652 11.8 324 5.8

Vietnam 2,002 32 1.6 365 18.2 293 14.6

China 1,478 23 1.6 162 11.0 133 9.0

Peru 373 14 3.8 51 13.7 38 10.2

Laos 284 12 4.2 49 17.3 36 12.7

Ukraine 93 12 12.9 21 22.6 17 18.3

Haiti 753 11 1.5 58 7.7 53 7.0

Republic of Korea 461 11 2.4 56 12.1 54 11.7

Burma / Myanmar 426 9 2.1 60 14.1 47 11.0

Dominican Republic 296 8 2.7 31 10.5 27 9.1

Ecuador 307 8 2.6 31 10.1 26 8.5

Guatemala 777 8 1.0 61 7.9 49 6.3

Ethiopia 635 7 1.1 60 9.4 58 9.1

*Total cases with positive cultures and initial susceptibilities performed **TB isolates with any first-line drug resistance (INH, RIF, ethambutol [EMB], PZA) Source: Robert H. Pratt, National Tuberculosis Surveillance System, Division of Tuberculosis Elimination, Centers for Disease Control and Prevention (email communication, November 14, 2014).

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Drug resistance is also more common in TB patients who reported having had previous TB. In the United States in 2013, 4.2% of all patients who reported previous TB

had MDR-TB, whereas only 1.2% of patients who did not report previous TB had MDR-TB.

These differences in percentages with MDR-TB were evident among both U.S.-born

patients (2.2% with previous TB vs. 0.3% without previous TB) and foreign-born patients

(5.1% with previous TB vs. 1.7% foreign-born patients without previous TB).

Sources of drug-resistant TB in the United StatesThere are 4 primary sources that explain the epidemiology of drug-resistant TB in the

United States:

• Resistance acquired during treatment in the United States

• Recent transmission of drug-resistant M. tuberculosis

• Reactivation of latent drug-resistant TB infection

• Entry of patients into the United States with active drug-resistant M. tuber-culosis disease

A cross-sectional study of 92 MDR-TB cases reported in the United States 2007-2009

determined that:

• 5% of patients had a documented previous episode of TB in the United Statesand likely relapsed with acquired drug-resistant disease.

• 22% of MDR-TB cases were the result of recent transmission.

• 41% had reactivation disease (one-third of those with reactivation disease had aprevious episode of TB in another country, indicating possible acquired resistanceoutside of the United States).

• Another 22% occurred in patients originating from another country whoentered the United States with active TB disease.

• 10% could not be classified because there were insufficient data.

MDR-TB transmission has been documented across the world, with a 2010 report of half

of MDR-TB cases occurring within individuals with newly-identified TB (rather than previ-

ously-treated TB), in 30 countries.

MDR-TB: A staggering cost for a small percentage of TB cases

A 2014 study by Marks, et al., of MDR-TB patients in the United States in 2005-2007 determined that

the direct costs to treat drug-resistant TB averaged $134,000 per MDR-TB patient and $430,000 per

XDR-TB patient. In contrast, the estimated cost per non-MDR-TB patient was $17,000.

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How is drug resistance generated? Drug resistance is generated at the molecular level when genes responsible for the spe-cific form of drug resistance (e.g., rpoB for rifampin) of M. tuberculosis develop a spon-taneous mutation. The prevalence of resistant mutants associated with each first-line

drug used to treat TB has been estimated, and resistance to new drugs (e.g., bedaquiline) has already been identified. A typical pulmonary cavity will contain an estimated 107 to 109 organisms, therefore making it likely that some organisms in

these cases may exhibit a spontaneous mutation for resistance. See Table 2.

TABLE 2.

Select anti-tuberculosis drugs and prevalence of resistant mutants

DrugYear

introduced

Prevalence of resistant mutants within a wild-type population of M. tuberculosis bacteria

Streptomycin 1945 3.8 x 10-6

Isoniazid 1952 3.5 x 10-6

Pyrazinamide 1952 1.0 x 10-5

Ethambutol 1962 3.1 x 10-5

Rifampin 1967 1.2 x 10-8

Bedaquiline 2013 ?

Within wild-type populations, resistance to more than one TB drug is even rarer as resis-

tance to the various drugs is not linked genetically. Inherent resistance to more than one

TB drug is the product of the prevalence of resistance to the individual drugs.

• INH and RIF: 3.5 x 10-6 x 1.2 x 10-8 equals 4.2 x 10-14

Mutations conferring drug resistance to M. tuberculosis become important for the TB

patient when amplified by health care system-related factors and/or patient behaviors.

Contributors to the development of acquired resistance during treatment for TB include:

inadequate clinical management, poor adherence, drug malabsorption, and unstable

drug supply. Enhancers of transmission of MDR-TB include factors that extend the

infectious period; e.g., delayed diagnosis and/or delayed treatment initiation with an

appropriate regimen, and delayed bacteriological conversion of sputum. Inadequate

infection control can also contribute to transmission of MDR-TB.

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In a patient with active TB disease, factors that create or amplify drug resistance include:

• The patient may not take all the drugs prescribed, due to any of the following factors:

• Lack of resources

• Intolerance/toxicity

• Misunderstanding

• Interrupted drug supply

• Disbelief in the diagnosis

• Disbelief in the efficacy or necessity of the treatment

• Chaotic lifestyle; substance abuse

• Cultural issues

• Pregnancy

• Neuropsychiatric disease

• There may be a dispensing or administration error regarding the correct dose.

• The patient may not be prescribed the appropriate dose.

• The patient may not absorb the full dose of medication and/or have disease in areas where the penetration of one or more of the drugs may be impaired.

• The provider may not prescribe an adequate TB regimen.

• The patient’s organism may already be resistant to one of the TB drugs prescribed, leaving an unrecognized suboptimal TB regimen.

• The patient may have been incorrectly diagnosed as having latent TB infection (LTBI), rather than active TB disease, and treated with monotherapy.

• The TB patient may be taking therapy for another disease. That therapy may coinci-dentally contain a single drug active against TB (rifabutin in an HIV patient for Myco-bacterium avium complex [MAC] prophylaxis; a fluoroquinolone for community- acquired pneumonia).

• The patient may take TB medicines without a prescription (sometimes available over-the-counter outside the United States, or if taking medications belonging to someone else).

• The TB medicines may interact with other drugs being taken by the patient.

Clinically significant drug resistance usually emerges after 1 to 3 months of administra-tion of an inadequate drug regimen.

If the patient starts an effective TB regimen and then stops taking all the TB drugs at the same time, the population of bacteria usually remains susceptible.

This is one of the major advantages of directly observed therapy (DOT): either the

patient takes all the drugs or none of the drugs. This is also the benefit of combination

formulations such as INH/RIF or INH/RIF/PZA in a single product. The patient either

takes all drugs or none—reducing risk of development of resistance.

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Summary

• Globally in 2014, an estimated 480,000 people developed MDR-TB and 190,000 people died from MDR-TB. By 2015, 105 countries had reported at least one case of XDR-TB. More than half of the global burden of MDR-TB is currently in three countries: India, China, and the Russian Federation.

• Despite recent improvements in early identification and enrollment into treatment, high-burden countries often lack the resources needed to ensure quality of care for treatment success.

• Ninety percent of MDR-TB cases in the United States occur among the foreign-born.

• Fifteen percent of MDR-TB patients in the United States had pre-XDR or XDR-TB.

• Risk factors for INH-resistant and MDR-TB in the United States include country-of-origin, recent arrival (within 2 years) in the United States, previous TB, and exposure to an individual with INH-resistant or MDR-TB during the infectious period.

• The percentage of TB patients with MDR-TB is not increasing in the United States, but the percentage of U.S.-born TB patients with INH resistance, and PZA resistance overall, is increasing in the United States.

• The increase in INH-resistant TB is troubling because it is one mutation away from becoming MDR-TB.

• It is essential to implement strategies to assure DOT and completion of an adequate regimen in order to reduce development or amplification of drug resistance.

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References• Andries K, Villellas C, Coeck N, et al. Acquired resistance of Mycobacterium tuberculosis to bedaquiline.

PLoS ONE. 2014;10;9(7):e102135.

• Caminero JA. Multidrug-resistant tuberculosis: epidemiology, risk factors and case finding. Int J Tuberc Lung Dis. 2010;14:382-390.

• Canetti G. Present aspects of bacterial resistance in tuberculosis. Am Rev Respir Dis. 1965; 92: 687-703.

• Centers for Disease Control and Prevention. Provisional CDC guidelines for the use and safety monitor-ing of bedaquiline fumarate (Sirturo) for the treatment of multidrug-resistant tuberculosis. MMWR. 2013;62(No. RR-9).

• Centers for Disease Control and Prevention. Reported Tuberculosis in the United States, 2013. Atlanta, GA: U.S. Department of Health and Human Services, CDC, October 2014.

• Kurbatova EV, Cavanaugh JS, Dalton T, Click ES, Cegielski JP. Epidemiology of pyrazinamide-resistant tuberculosis in the United States, 1999-2009. Clin Infect Dis. 2013;57(8):1081-1093.

• Marks SM, Flood J, Seaworth B, et al. Treatment practices, outcomes, and costs of multidrug-resistant and extensively drug-resistant tuberculosis, United States, 2005–2007. Emerg Infect Dis. 2014;20(5): 812-820.

• Moonan PK, Teeter LD, Salcedo K, et al. Transmission of multidrug-resistant tuberculosis in the USA: a cross-sectional study. Lancet Infect Dis. 2013;13(9):777-784.

• Royce S, Falzon D, van Weezenbeek C, et al. Multidrug resistance in new tuberculosis patients: burden and implications. Int J Tuberc Lung Dis. 2013;17(4):511-513

• Taylor AB, Kurbatova EV, Cegielski JP. Prevalence of anti-tuberculosis drug resistance in foreign-born tuberculosis cases in the U.S. and in their countries of origin. PLoS ONE. 2012;7(11) e49355.

• World Care Council. Patients’ Charter for Tuberculosis Care. 2006. Available at: http://www.currytb-center.ucsf.edu/international-research#patients-charter. Accessed November 1, 2015.

• World Health Organization. Drug-Resistant TB Surveillance & Response. Supplement: Global Tubercu-losis Report 2014. Available at: http://www.who.int/tb/publications/global_report/gtbr14_supplement_web_v3.pdf. Accessed December 30, 2015.

• World Health Organization. Global Tuberculosis Report, 2015. Available at: www.who.int/tb/publications/ global_report/en/. Accessed December 30, 2015.

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Epidemiology & BackgroundMDR-TB remained stable over the same time period. Overall, drug-resistant...

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