(Adds comments on tests from WHO and head of lab)

JAKARTA, Aug 7 (Reuters) - Thirteen people from a village in North Sumatra are due to be tested for bird flu after falling sick, Indonesian health officials said on Thursday.

The 13, from Air Batu village, were hospitalised this week after suffering fever, but their conditions had improved on Thursday and they might not be suffering from the disease, a health official said.

A bird flu surveillance team from Indonesia's health ministry has been sent to the area.

"Although they found dead chickens in the area, the symptoms are not like bird flu," said Erna Tresnaningsih, the health ministry's director of animal-borne disease control.

Sari Setiogi, a spokeswoman for the World Health Organisation in Geneva, and the head of a laboratory in Jakarta conducting the tests said the findings were expected later on Thursday.

A seven-year-old girl and an eight-month-old child were being treated in Adam Malik hospital in North Sumatra's capital Medan with Tamiflu, the medication most often used to treat bird flu, said hospital spokesman Sinar Ginting.

The country's largest known cluster of bird flu cases in humans occurred in May 2006 in the Karo district of North Sumatra province, where as many as 7 people in an extended family died.

The WHO said at the time that limited human-to-human transmission could not be ruled out but that the virus samples from the scene did not show any significant genetic mutations.

Ginting was quoted by media as saying on Wednesday that not all the patients were believed to have had contact with fowl, which is the most common way of contracting the H5N1 bird flu virus, after some chickens in the area had died suddenly and were found to have been infected.

Suspected cluster cases can raise concerns about rare human-to-human transmission or that the virus might have mutated into a form that can pass easily among people, triggering a pandemic.

Bird flu remains mainly an animal disease but experts fear the H5N1 virus might mutate into a pandemic strain that would sweep the globe, possibly killing millions and hobbling economies.

Health experts say monitoring of the virus across Indonesia's thousands of islands to detect any genetic changes is vital, but there has been some confusion over the government's stance on reporting cases.

Indonesian Health Minister Siti Fadillah Supari, who has clashed with the international community over virus sharing, said in early June her ministry would only report cases every six months, although the ministry has reported three deaths since.

The virus is known to have infected 385 people in 15 countries, killing 243 of them since late 2003, according to the WHO's June 19 tally.

Indonesia reported on Sunday that a 19-year-old man died from bird flu last week, bringing the total death toll in the Southeast Asian country to 111, the highest of any nation.

(Additional reporting by Geneva bureau)

(Reporting by Olivia Rondonuwu; Editing by Ed Davies and David Fogarty)

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