Global rise of multidrug resistant TB threatens to derail progress

The rise of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) threatens to derail decades of progress in controlling the disease, according to a new report in The Lancet Respiratory Medicine published on World TB day on 24th March.

Although a small number of repurposed and new drugs have recently become available to treat drug-resistant TB, the authors warn that without accurate diagnostic tests to deliver individually targeted treatments, clear prescription guidelines on appropriate use and improved control efforts to prevent transmission, optimal dosing and administration, and well-functioning health care systems, the effectiveness of the drugs could be rapidly lost.

Approximately 1 in 5 cases of TB are now resistant to at least one major anti-TB drug and approximately 5% of all cases of TB are classed as MDR or XDR. Globally in 2015, there were an estimated 4,80,000 cases of MDR-TB. But, migration and travel mean that highly drug-resistant TB strains have emerged in almost every part of the world.

MDR and XDR-TB are associated with high mortality, are a threat to health-care workers, prohibitively expensive to treat, and are therefore a serious public health problem. The mortality rate is extremely high at around 40% for patients with MDR-TB, and 60% for patients with XDR-TB.

Of the US$6.3 billion available in 2014 to respond to the global TB epidemic, about a third ($1.8 billion) was for MDR-TB (despite drug resistant TB forming only 5% of the total caseload).

TB is caused by a bacterial species called Mycobacterium tuberculosis and is treated with a combination of antibiotics. The treatment of TB was revolutionised in the 1950s with the introduction of three antibiotics: streptomycin, isoniazid, and para-aminosalicylic acid. The extensive overuse and abuse of antibiotics worldwide has led to a rise in bacteria that are drug resistant. Drug-resistant genetic mutations in the bacteria can occur as a result of inadequate treatment or can be passed on from one bacteria to another. Bacteria can acquire multiple drug resistance traits over time, making them resistant to several different types of antibiotics.

Until recently, it was thought that drug-resistant strains of TB were less transmissible, and that MDR- and XDR-TB was mainly acquired by individuals as a result of poor compliance to treatment. However, recent molecular and epidemiological studies, outlined in the Commission, have challenged this belief. In most regions of the world, drug-resistant TB is now predominantly caused by transmission, with an estimated 95.9% of new cases infected with MDR-TB strains due to the drug resistant bacteria spreading from one person to the next.

The Commission sets out key priority actions for the next two, five and ten years for the research and policy communities, and outlines key treatment recommendations and procedures for doctors treating patients with MDR- or XDR-TB.

The report is being launched at a conference at the University of Cape Town, South Africa, co-funded by the South African Medical Research Council and the South African Thoracic Society.