The comment that "with perhaps rare exceptions, people are not getting sick from other people. Of the many hundreds of people who were in close contact with the H7N9 patients, all the care-givers, neighbors, family members, and so on, there are only a very few cases where these contacts have become ill as well." exemplifies the search for symptomatic illness.
However there is still an opportunity to test the contacts using sensitive laboratory methods.
These results will be very important for ruling out (or in) the potential for stealthy H7N9 spread among people without predetermined clinical signs and symptoms.