Image copyright SPL Image caption About 1.5 million people died in 2013 from TB, including 360,000 people who were HIV positive.

The World Health Organization has revised up its estimate of how many people have tuberculosis by almost 500,000.

In 2013 nine million people had developed TB around the world, up from 8.6 million in 2012, the WHO said.

However, the number of people dying from TB continued to decline, it added.

TB campaigners said that one of the biggest problems in tackling the deadly disease was gauging how many people were affected.

Long-term decline

About 1.5 million people had died in 2013 from TB, including 360,000 people who had been HIV positive, the WHO said in its Global Tuberculosis Report 2014. And in 2012, there had been 1.3 million tuberculosis deaths.

The WHO said its report underlined that a "staggering number of lives are being lost to a curable disease and confirms that TB is the second biggest killer disease from a single infectious agent".

One of the main factors in revising up the number of cases had been improved national data collection, the organisation added.

In the long-term, the mortality rate from TB had fallen, dropping by 45% since 1990, the WHO said.

Undiagnosed TB

Since then, the number of people developing the disease had declined by about 1.5% per year. But about three million people with TB had remained undiagnosed in 2013, the WHO added.

One of the biggest issues facing organisations tackling the disease was the number of undiagnosed cases, said tuberculosis charity TB Alert.

"The fact that three million people are missing out on treatment every year explains why there are still so many avoidable deaths from tuberculosis," said TB Alert chief executive Mike Mandelbaum.

"By strengthening health systems, especially in high-incidence countries, we can turn the tide of this global epidemic and finally move into sight of eradicating this disease," he added.

The WHO report also said:

Most of the people who developed TB in 2013 were in South East Asia and the Western Pacific

India accounted for 24% of cases alone

China saw 11% of total cases

A further quarter were in the Africa, which had the highest rates of cases and deaths relative to the population

The WHO said that insufficient funding was hampering efforts to combat the disease. An estimated $8bn (£5bn) was needed each year, but there was an annual shortfall of $2bn, it said.

Drug resistant 'epidemics'

Tuberculosis that is resistant to drugs, which is harder to treat and cure, had accounted for 3.5% of new cases in 2013, the WHO said.

Globally, 5% of TB cases were estimated to be drug resistant. But in some parts of the world, including Eastern Europe and Central Asia, there were "severe epidemics", the WHO said.

For example, in Belarus, 35% of new cases were drug resistant.

"Improved diagnostic tools and access mean that we are detecting and treating more cases," said Dr Karin Weyer, WHO coordinator for laboratories, diagnostics and drug resistance.

"But the gap between detecting and actually getting people started on treatment is widening and we urgently need increased commitment and funding to test and treat every case," she added.

Extensively drug-resistant TB, which is even more difficult to treat than drug-resistant TB, had been reported in 100 countries, the WHO said.

Aid network Medecins Sans Frontieres said that the rise of drug resistant TB, especially in the former Soviet Union, was of "critical concern".

"Access to proper treatment is drastically low: only one person in five with multidrug-resistant TB receives treatment; the rest are left to die, increasing the risk to their families and communities and fuelling the epidemic," said Medecins Sans Frontieres TB advisor Dr Grania Brigden.

"This dismal news must serve as a wake-up call for governments, donors and drug companies," she added.