The CDC reports shows the incidents occurred in a boy under five in Indiana and a girl under five in Pennsylvania.

The CDC said that for the boy, no direct exposure to swine was identified. However, a caretaker reported direct contact with asymptomatic swine in the weeks before the boy's illness onset and provided care to the child two days before illness onset. No respiratory illness was identified in any of the child's family or close contacts, the boy's caretaker, or in the family or contacts of the caretaker.

For the girl, on 16 August she was reported to have visited an agricultural fair, where she had direct exposure to swine and other animals. No additional illness in the girl's family or close contacts has been identified, but illness in other fair attendees continues to be investigated. No additional confirmed swine-origin influenza virus infections have been identified thus far, the CDC said.

Both the boy and the girl completely recovered from the viruses which were influenza A H3N2.

THe CDC said that influenza A viruses are endemic in many animal species, including humans, swine, and wild birds, and sporadic cases of transmission of influenza A viruses between humans and animals do occur, including human infections with avian-origin influenza A viruses (i.e., H5N1 and H7N7) and swine-origin influenza A viruses (i.e., H1N1, H1N2, and H3N2).

Genetic analysis can distinguish animal origin influenza viruses from the seasonal human influenza viruses that circulate widely and cause annual epidemics.