FACTBOX: U.N. revisions to global disease tolls

(Reuters) - The World Health Organization on Tuesday doubled its estimate of the number of HIV-positive people who catch and die from tuberculosis, the latest in a series of major revisions of global disease tolls.

Such revisions have direct implications for the Western governments who have provided billions of dollars to fight diseases such as HIV/AIDS, malaria and tuberculosis based on international estimates of their prevalence.

Pharmaceutical companies have also invested heavily in drugs, diagnostics and vaccines for the trio of diseases the United Nations pledged to tackle in its Millennium Development Goals, and which the Global Fund to Fight AIDS, Tuberculosis and Malaria has devoted itself to.

Following are the details of recent disease toll revisions:

TUBERCULOSIS - March 2009 - The WHO doubled its estimate of the number of people co-infected with both tuberculosis and HIV, as well as the number of people dying as a result, due to "better analyses, better data, and better methodology."

It believes tuberculosis killed about 1.8 million people in 2007 -- 1.3 million HIV-negative people and 456,000 who were also infected with the AIDS virus, deaths from which are strictly classified in health statistics as HIV fatalities.

The most recent Global Tuberculosis Control report includes direct measurements from 64 states, out of a total of 212 countries and territories from which information was requested, the WHO said. The previous report had included direct measurements from just 15 countries.

MALARIA - September 2008 - The WHO said 247 million people were infected with malaria worldwide in 2006, slashing its prior estimate that 350 million to 500 million people were afflicted each year from the mosquito-borne disease. New calculation methods, including the use of up-to-date Asian maps that showed urbanization had destroyed mosquito breeding habitats, also reduced the global malaria death toll estimate by about 10 percent, although the WHO said it was not clear if actual cases and deaths had fallen.

WHO Director-General Margaret Chan told a news conference that less than one third of her agency's 193 member states had reliable systems to monitor and document malaria and other serious diseases whose initial symptoms can resemble flu.

HIV/AIDS - November 2007 - Revised data from India caused UNAIDS to slash its estimate of how many people worldwide are infected with the AIDS virus to 33 million, from nearly 40 million previously.

The U.N. agency said it overestimated how many people are infected with the incurable virus, and said better methods of collecting data showed it was not as common as earlier feared.

"These improved data present us with a clearer picture of the AIDS epidemic, one that reveals both challenges and opportunities," UNAIDS said in a statement at the time.

(Compiled by Laura MacInnis)