A man infected with H5N2 bird flu, the first confirmed human infection with the strain, died from multiple factors, the WHO said on Friday, adding that investigations were ongoing.
The World Health Organization on Wednesday announced 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 a week later and died 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.
His body was tested for flu and other viruses, and H5N2 was detected, Lindmeier said.
Seventeen hospital contacts were identified but all tested negative for influenza.
In the man's place of residence, 12 contacts in the weeks beforehand were identified. All likewise tested negative.
"The infection of H5N2 is being investigated to see whether he was infected by somebody visiting or by any contact with any animals before," Lindmeier said.
The WHO on Wednesday said that the source of exposure to the virus was unknown, though H5N2 viruses have been reported in poultry in Mexico.
The United Nations' health agency assesses the current risk to the general population posed by the virus as low.
Later on Friday, the WHO said a two-and-a-half-year-old girl tested positive for H5N1, a different strain of bird flu, and needed hospital intensive care treatment in Australia after returning from India.
"This is the first confirmed human infection caused by avian influenza A(H5N1) virus detected and reported by Australia," a statement said.
"The exposure likely occurred in India" where the girl had travelled, and where this group of "viruses has been detected in birds in the past," the WHO added.
The girl had travelled to Kolkata from February 12 to 29, returned to Australia on March 1 and was admitted to a hospital in in the southeastern Victoria state the following day.
The girl is reported to be well, the WHO said, while no relatives in either Australia or India have developed symptoms.
H5N1 first emerged in 1996 but since 2020, the number of outbreaks in birds has surged 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 WHO said that from 2003 to May 22 this year, 891 cases of human H5N1 infections, including 463 deaths, were reported from 24 countries.
The human cases recorded in Europe and the United States since the virus surged have largely been mild.
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.
Markus Lipp, senior food safety officer at the UN's Food and Agriculture Organization, said the risk of contracting avian influenza through 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.
"Humans do not have avian influenza receptors in their gastrointestinal tract, contrary to certain animal species, as far as we know. So there is a very slim likelihood, just from that perspective."
