Multi-drug Resistant Tuberculosis

The Critical Challenge of Drug Resistance

Anyone can be infected with tuberculosis (TB), but the overall proportion of infected individuals who progress to active disease is approximately 10%.^1,10 Although efficacious anti-TB drugs have been available for decades, drug resistance in Mycobacterium tuberculosis has also been a challenge.

TB bacteria can acquire resistance to antibiotics during drug treatment if a patient with TB:

• does not complete the full course of treatment
• is otherwise inadequately treated (eg, caregiver errors occur in prescribing or administration, or a poor-quality formulation is supplied)

This type of drug resistance, called acquired drug resistance, occurs in TB because a patient’s bacterial population survives for several months during treatment.^3,13

• An incomplete course of TB therapy is considered an important risk factor in the development of TB drug resistance. Patient adherence to therapy can be problematic, particularly in cases where access to proper medical care is lacking to support patients in completing therapy.^4,12
• Prior treatment with anti-TB drugs is considered a strong determinant of contracting a drug-resistant strain.¹¹

Primary drug resistance, on the other hand, occurs when a person contracts an infecting strain of TB that is already resistant to one or more anti-TB drugs.¹³

Strains of TB resistant to treatment with at least isoniazid and rifampin are known as multi-drug resistant tuberculosis (MDR-TB). MDR-TB is a critical issue to address because it impacts various regions.⁹

The total number of MDR-TB cases in the US is comprised of MDR-TB among US-born and foreign-born TB cases. The percentage of MDR-TB in both populations show opposite trends. Of the total number of reported primary MDR-TB cases, the proportion occurring in foreign-born persons increased from 25.3% (103 of 407) in 1993 to to 84.5% (82 of 97) in 2017. The number of MDR-TB cases in US-born persons decreased from 73.9% (301 of 407) in 1993 to 15.5% (15 of 97) in 2017.⁴

The Centers for Disease Control and Prevention estimated there were 128 new MDR-TB cases in the US during 2018.¹⁴

Levels of Drug Resistance

Strains of TB may exhibit various ranges of drug resistance, including MDR-TB. These levels of resistance can be classified according to the chart below.

• Drug-sensitive TB (DS-TB): Sensitive to first-line agents
• MDR-TB: Strains of TB resistant to treatment with at least isoniazid and rifampin

Classification of TB and Clinical Definition of MDR-TB⁹