A recent article in Reuters has argued that due to our inability to easily see H7N9 in poultry, it may be more common than formerly expected. For reference, H7N9 is an avian subtype of influenza A not to be confused with H5N6, another subtype. The difference between these two subtypes can be seen easily in their fatality in humans. The latter struck South Korean poultry at the end of 2016 and led to massive culls of birds, but no human deaths. On the other hand, the former, H7N9 has been fatal in 100 or more people in the last few months, but is often asymptomatic in the birds that it infects.
Though unable, at this point, to spread via human to human contact, H7N9 can be easily passed between birds and it is interactions with these infected birds that lead to human infection. Because of this, the CDC labels H7N9 has being low risk, but marks it (on its Influenza Risk Assessment Tool) as the influenza subtype with the greatest potential to cause a pandemic. Because of this potential, the CDC is keeping an eye on H7N9 and preparing for it by checking the H7N9 candidate vaccine viruses to see if they need to be updated for the latest epidemic and seeing if the latest strains of H7N9 are still susceptible to the neuraminidase inhibitors we have available.