KUALA LUMPUR (Reuters) - Some cases of human bird flu in Indonesia have been variously misdiagnosed as dengue fever and typhoid, resulting in the late administration of drugs, a leading doctor in the country said on Friday.

Indonesia has had the highest number of human H5N1 cases in the world and while mortality rates are around 60 percent in other places, the figure is highest, or at 81 percent, in Indonesia.

Sardikin Giriputro, director of the Sulianti Saroso Infectious Disease Hospital in Indonesia, told an infectious disease conference in Kuala Lumpur that misdiagnoses and the late administration of drugs were partially responsible for the high mortality rates.

"It (H5N1) is misdiagnosed initially as dengue, bacterial pneumonia, typhoid and upper respiratory tract infection because of similar clinical features (symptoms)," Giriputro said.

Indonesia has had 135 confirmed human H5N1 cases from late 2003 to May 2008 and 110 resulted in deaths. The country reported two more confirmed cases this week, but these were not reflected in Giriputro's figures.

Oseltamivir, otherwise known by its brand Tamiflu, is considered the drug of choice against bird flu and Giriputro said fatalities mounted the later the drug was administered.

The survival rate was very high when Tamiflu was given less than 2 days after the onset of symptoms, but that plunged the later the drug was given.

"It's best if given less than 24 or 36 hours after the onset of symptoms," he told Reuters later.

While rapid test kits are now used to diagnose the disease in animals, Giriputro said these tools were much less reliable in people.

"It depends on the viral load (in samples taken from patients)," he said, adding that test results could turn out negative even if the person was infected with H5N1, simply because there was not enough virus in samples taken.

In a bid to reduce the death rate, the Indonesian government has begun distributing Tamiflu to health centers in areas where H5N1 cases have occurred.

"When doctors see influenza-like illnesses and where there is evidence of contact with sick poultry, then they give Tamiflu (without waiting for laboratory results)," Giriputro said.

While H5N1 remains essentially a disease among birds, experts have warned for years now that it could trigger a pandemic, killing millions of people, if it ever manages to become easily transmitted among humans.