WASHINGTON, Aug 13 (Reuters) - Late diagnosis and treatment means that more than 80 percent of people infected with H5N1 avian influenza in Indonesia have died, researchers reported on Wednesday.

An analysis of outbreaks in Indonesia, the country hardest hit by bird flu, affirms that quick treatment with antiviral drugs can save lives. But local health care workers are not properly trained in diagnosing bird flu and often do not have the needed drugs to treat it.

Indonesia has had one-third of the world's known cases of human infection with H5N1 avian influenza. It rarely infects people but globally has killed 243 out of 385 sickened since 2003. In Indonesia, 135 people have been infected and 110 have died, according to the World Health Organization.

Dr. Toni Wandra of the Ministry of Health in Jakarta and colleagues analyzed the known cases as of February and found it took on average six days for patients to be admitted to a hospital.

By the time they were admitted, 99 percent had a fever, 88 percent were coughing and 84 percent had breathing problems, they reported in the Lancet medical journal.

But for the first two days they were ill, most patients had hard-to-identify symptoms -- only 31 had both fever and cough, and nine had fever and breathing problems.

On average it took seven days to get oseltamivir -- Roche AG <ROG.VX> and Gilead Sciences Inc's <GILD.O> Tamiflu.

More than a third of patients who got Tamiflu within six days survived, compared to 19 percent treated at seven days or later survived.

This confirms other research that shows treatment with flu drugs such as Tamiflu needs to start right away to be effective, they said.

"There is a clear need to identify definite causes for high-case fatality," Wandra's team wrote.

"Poultry surveillance is being stepped up, and active human case finding by local health centers and village officials is being instituted in areas of poultry deaths."

Workers need to be trained in getting information about whether patients with flu-like symptoms were around sick poultry, they added.

"Finally, all health-care workers should be trained in case management of early H5N1 influenza, and should be equipped with oseltamivir to enable timely administration."

H5N1 currently infects mostly birds and has killed or forced the destruction of 300 million in Asia, Europe, the Middle East and Africa.

It rarely infects humans and almost all cases have been infected by sick birds. Doctors fear it could change into a form that easily infects people, in which case it could sweep the world, killing millions of people in months.

Tamiflu and GlaxoSmithKline's <GSK.L> and Biota's <BTA.AX> Relenza can treat the infection, but are in short supply, and a vaccine would take months or years to manufacture and deliver. (Reporting by Maggie Fox, editing by Will Dunham)

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