ISLAMABAD, Pakistan - World Health Organization bird flu experts were continuing investigations Wednesday to determine whether human-to-human transmission may have occurred in Pakistan's first cases involving people.

Four brothers and two cousins fell ill last month in Abbotabad, north of Islamabad, while other people, who slaughtered poultry in the same area and a nearby town, tested positive for the H5N1 bird flu virus this month.

Two of the brothers died but specimens were collected from only one. The cases were positive for H5N1 in initial government testing but WHO will conduct further analysis to confirm the results.

The WHO team visited a hospital in the northwestern city Peshawar Tuesday that treated some of the eight patients suspected of being infected with the H5N1 bird flu virus. They were working with doctors and nurses on how to handle suspected cases and improve infection-control measures.

"They want to go through the records in the hospital for the last month or two to see if there's been any upsurge in respiratory cases that weren't identified as H5N1 but which could actually be," said Gregory Hartl, a WHO spokesman in Geneva.

The WHO team will look to see which patients could have been exposed to the virus by infected birds and also whether human-to-human transmission could have occurred.

One of the brothers who survived, Mohammed Ishtiaq, said he was in hospital with flu symptoms after slaughtering chickens suspected of carrying bird flu without wearing protective clothing last month.

His brothers who died visited him in a hospital, he said.

Hartl said no new cases have been discovered but increased awareness has led to more people with flu-like symptoms being checked.

"What this is showing is that they're taking everything very, very seriously," Hartl said.

"Surveillance has been enhanced, more people are reporting cases and more people have been sensitized on the health care worker side of the need to notice."

Pakistan has requested additional supplies of the antiviral Tamiflu as a precaution.

At least 208 people have died worldwide from the virus, which began plaguing Asian poultry stocks in late 2003, WHO said. It remains hard for people to catch but scientists worry it could mutate into a form that spreads easily among people, potentially sparking a pandemic.