LONDON (AP) — The World Health Organization says the number of people diagnosed with tuberculosis fell slightly last year but 3 million people are going undiagnosed and untreated.

WHO estimates that 8.6 million people were diagnosed with TB and 1.3 million died in 2012. TB most often attacks the lungs and can usually be treated with antibiotics.

The agency also notes a rise in drug-resistant strains, which require more toxic and expensive drugs. WHO says at least 16,000 people with drug-resistant TB aren't being treated worldwide.

The agency's numbers were based largely on estimates from governments and it has no solid data on how much drug-resistant TB is spreading.