Multi-drug-resistant Tuberculosis - Epidemiology

Epidemiology

Cases of MDB tuberculosis have been reported in every country surveyed. MDB-TB most commonly develops in the course of TB treatment, and is most commonly due to doctors giving inappropriate treatment, or patients missing doses or failing to complete their treatment. Because MDR tuberculosis is an airborne pathogen, persons with active, pulmonary tuberculosis caused by a multidrug-resistant strain can transmit the disease if they are alive and coughing. TB strains are often less fit and less transmissible, and outbreaks occur more readily in people with weakened immune systems (e.g., patients with HIV). Outbreaks among non immunocompromised healthy people do occur, but are less common. A 1997 survey of 35 countries found rates above 2% in about a third of the countries surveyed. The highest rates were in the former USSR, the Baltic states, Argentina, and China, and was associated with poor or failing national tuberculosis control programmes. In Moldova, the crumbling health system has led to the rise of MDR-TB. It has been known for many years that INH-resistant TB is less virulent in guinea pigs, and the epidemiological evidence is that MDR strains of TB do not dominate naturally. A study in Los Angeles, California found that only 6% of cases of MDR-TB were clustered. Likewise, the appearance of high rates of MDR-TB in New York City in the early 1990s was associated with the explosion of AIDS in that area.