Amy Maxmen | (TNS) KFF Health News Bird flu cases have more than doubled in the country within a few weeks, but researchers can’t determine why the spike is happening because surveillance for human infections has been patchy for seven months. Just this week, California reported its 15th infection in dairy workers and Washington state reported seven probable cases in poultry workers. Hundreds of emails from state and local health departments, obtained in records requests from KFF Health News, help reveal why.