More than 30 percent of global tuberculosis (TB) cases — or 3 million total — went undiagnosed or unreported last year, the World Health Organization (WHO), a United Nations agency, revealed Wednesday.

Those "missed cases" represent one of the challenges in the fight against TB, an infectious disease that most commonly affects the lungs and is transmitted by bacteria in the air, often when infected persons cough or breathe on others.

Health officials worry about the consequences of such an issue, despite the great strides that have been made in TB detection and treatment over the past decade. For example, the overall mortality rate from TB has dropped by nearly half, the WHO reported. But there are still a number of "targets not on track."

In 2012 alone, 1.3 million of the 8.6 million people who developed TB died of the disease. An estimated 74,000 were children.

TB infections and deaths are more prevalent among men, but the disease remains one of the top three killers of women, the WHO reported.

While seven of 22 countries with high concentrations of TB — including China, Brazil, and Uganda — have already met WHO targets for reductions in TB infections and deaths ahead of a 2015 deadline, 11 countries, including Russia, South Africa and Pakistan, are "not on track to reach one or more of the three targets for reductions in incidence, prevalence and morality," the agency reported.



Overall, the decline of TB cases has been "slow," at a rate of 2 percent each year.

Some 13 percent of the 8.6 million people diagnosed with TB last year were also HIV-positive, and 75 percent of the sufferers of the two diseases were in Africa.

The majority of cases worldwide were in Southeast Asia, followed by Africa and the Western Baltic. Cases in India alone accounted for 26 percent of the global total.

Prospects aren't entirely grim, though. The WHO has successfully achieved some important milestones in combatting the global TB crisis, the report showed. The organization set out to help reduce deaths from TB by 50 percent in 1990. In 2012, the mortality rate had fallen by 45 percent. Some 56 million TB patients have been successfully treated since 1995, and 22 million lives have been saved.

Chief among the suggestions the WHO offers for meeting its 2015 targets are "reaching the missed cases" and greater "high-level political will and leadership and more collaboration among partners including drug regulatory authorities, donor and technical agencies, civil society and the pharmaceutical industry" to address TB as a substantial public health crisis.

The WHO reported it is missing $2 billion of the annual $7.8 billion it estimates is needed for a "full response" to the epidemic among low and middle-income countries by 2015.

More than 50 companies are currently helping to develop new diagnostic tests.