Over 1 million people are estimated to live in the favelas of Sao Paulo.  As with other slums, the majority of these residents experience severe water and sanitation stress.  Many also live in very close quarters with other humans and animal species, leading to a perfect “Petri dish” for interspecies viral mutation. 

In this scenario, poor sanitation and high population densities lead to a new outbreak of virulent influenza, which would come to be known as H6N1 to scientists.  The crisis began in December 2015, when awave of pigs and poultry in one of Sao Paulo’s largest slums fell ill.  The infected animals were lethargic, exhibiting high fevers and hemoraging mucus membranes, followed  quickly by death within a day.  Although the owners of the animals were concerned, they were disconnected from official health and sanitation networks and were unable or unwilling to report the deaths the authorities. 

Within weeks the disease had spread to humans and aid workers within the slum began to notice a spike in flu-like symptoms.  By this point several weeks had passed and the virus had reached beyond the confines of the slum and was already spreading throughout the country.  By the time the WHO teams arrived in the country on December 12th, the first human outbreaks were already occuring and additional reports were coming in from other parts of South America, Mexico, and Miami and New York.  The team immediately realised a crisis was brewing and the WHO immediately raised the pandemic alert to Phase 4, noting a new strain in animals which also appeared in a small number of human beings.