Tuberculosis is the leading cause of infectious death worldwide,  killing approximately 1.6 million people each year. However, research and development for new TB drugs came to a virtual standstill after the 1960s. Today, a four-drug combination therapy exists, but it takes six months or more to be effective. This requires a degree of monitoring (See Direct Observational Therapy, Short-course) beyond the capacity of the health infrastructure in many countries, and adequate TB treatment is not available to more than half of the most infectious cases. This can inhibit control of the disease and fuel the rise of drug resistance (See antimicrobial resistance).