July 3 (Reuters) - U.S. doctors treating a man who sparked international concern because he flew after being diagnosed with a dangerous form of tuberculosis said he in fact is infected with a somewhat milder form, multidrug-resistant TB, or MDR TB.

Here are some facts about MDR TB:

-- An estimated 500,000 people globally have MDR TB, according to the World Health Organization.

-- In MDR TB, the bacteria that cause the disease are resistant to the two most powerful anti-TB drugs, isoniazid and rifampicin.

-- MDR TB is called extensively drug-resistant TB or XDR TB if it also resists antibiotics in a class called fluoroquinolones, and at least one of three injectable second-line drugs -- capreomycin, kanamycin, and amikacin.

-- Only 70 percent of MDR TB cases are cured and only 30 to 40 percent of XDR TB cases can be cured.

-- WHO says there is probably no difference in the transmission of XDR-TB and any other forms of TB. The risk of becoming infected increases over time with contact.

-- Up to 90 percent of people infected with TB bacteria never develop TB disease, including those with MDR and XDR forms.

-- Symptoms of active disease include a cough with thick, cloudy mucus, sometimes with blood, for more than 2 weeks; fever, chills, and night sweats; fatigue and muscle weakness; weight loss; and in some cases shortness of breath and chest pain.

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