A man infected with H5N2 bird flu, the first confirmed human infection with the strain, died from multiple factors, the WHO said Friday, adding that investigations were continuing.

The World Health Organization announced Wednesday that the first laboratory-confirmed human case of infection with H5N2 avian influenza virus had been reported from Mexico.

Mexico's health ministry said the 59-year-old man had "a history of chronic kidney disease, type 2 diabetes (and) long-standing systemic arterial hypertension".

He had been bedridden for three weeks before the onset of acute symptoms, developing fever, shortness of breath, diarrhoea, nausea and general malaise on April 17.

The man was taken to hospital in Mexico City on April 24 and died later that day.

"The death is a multi-factorial death, not a death attributable to H5N2," WHO spokesman Christian Lindmeier told journalists in Geneva on Friday.

"The patient came to the hospital after weeks of multi-factorial background of multi other diseases," he said.

His body was subsequently routinely tested for flu and other viruses, and H5N2 was detected, Lindmeier said.

Seventeen contacts of the case in the hospital were identified. All tested negative for influenza.

In the man's place of residence, 12 contacts in the weeks beforehand were identified. All likewise tested negative.

"Investigations are ongoing. Serology is ongoing. That means the blood testing of contacts to see if there was any possible earlier infection," Lindmeier said.

"The infection of H5N2 is being investigated to see whether he was infected by somebody visiting or by any contact with any animals before."

The WHO said Wednesday that the source of exposure to the virus was unknown, though H5N2 viruses have been reported in poultry in Mexico.

Based on available information, the United Nations' health agency assesses the current risk to the general population posed by the virus as low.

- Low food risk -

Markus Lipp, senior food safety officer at the UN's Food and Agriculture Organization, said the risk of contracting avian influenza though eating poultry was "negligibly low".

"In all the hundred years of avian influenza... there has not been any demonstrated food-borne transmission," he told the media briefing via video-link from the FAO's headquarters in Rome.

"Animal handlers, of course, who are in extremely close contact with animals may get an infection but it's an occupational risk. It's not a food-borne transmission," he said.

"Humans do not have avian influenza receptors in their gastro-intestinal tract, contrary to certain animal species, as far as we know. So there is a very slim likelihood, just from that perspective."

Of all the food safety risks when eating poultry, "probably the lowest risk is connected to avian influenza", Lipp said.

- H5N1 spread -

A different variant of bird flu, H5N1, has been spreading for weeks among dairy cow herds in the United States, with a small number of cases reported among humans.

But none of them are human-to-human infections, with the disease jumping instead from cattle to people, authorities have said.

H5N1 first emerged in 1996 but since 2020, the number of outbreaks in birds has grown exponentially, alongside an increase in the number of infected mammals.

The strain has led to the deaths of tens of millions of poultry, with wild birds and land and marine mammals also infected.

The human cases recorded in Europe and the United States since the virus surged have largely been mild.