Indonesia reported its 101st death from bird flu on Wednesday, when a health ministry official confirmed that a 32-year-old man who had tested positive for bird flu did not survive.

A 32-year-old man from Tangerang west of Jakarta, died on Tuesday at Jakarta's Persahabatan hospital, Health Ministry official Toto Haryanto said, Reuters India reports.

Not only does his death bring Indonesia’s toll from the H5N1 virus to 101, but the source of infection has not been identified yet by authorities. It was initially suspected that he contracted the virus from pet doves kept in his neighborhood but testing revealed that the birds and other fowl in the neighborhood were not infected, Reuters reports.

“It's a big mystery that has yet to be solved,” Zulkarnain Hassan from the agricultural ministry's bird flu control unit in charge with investigating the source of infection, told Reuters. “There are three out of four people who died of bird flu this week whose virus source remains unknown.”

It was only Monday that the country hardest hit by the virus reported its 100th death, when a 23-year-old woman from East Jakarta and a 9-year-old boy from the capital’s outskirts were confirmed as victims of the virus, following test results. The source of infection in both cases is still unknown.

As of Wednesday, 101 Indonesians had died and 23 others had been infected but recovered, the Associated Press reports.

Reuters also quotes Emil Agustiono, a top national bird flu committee official, who explained the recent increase in deaths by citing weather conditions and poor sanitation. “The virus is happy when it's wet. It thrives during the rainy season ... combine that with poor sanitation and lack of awareness. The people in the slums are at greater risk.”

The vast majority of bird flu deaths have been linked with contact with contaminated poultry. As to the lack of awareness the official referred to, it was only last week that Reuters reported how veterinary workers in Bangladesh and India were thwarted in their efforts to cull potentially sick animals by locals that let their birds run free, arguing that they are healthy and thus exposing themselves to contamination.

More than 200 people have died over the past four years from bird flu; should the virus mutate into a form that is easily transmissible among humans, as experts fear, a pandemic would be the worst possible risk.