Two cats that belonged to Michigan dairy workers died after being infected with bird flu. But it's still not clear how the animals got sick or whether they spread the virus to people in the household,

Two indoor cats in the same county in Michigan were infected with H5N1 avian flu last May, likely via their owners who worked on dairy farms. Both cats had severe respiratory and neurologic illness and died,

But the study, whose publication was delayed by a pause in public communications by the agency, leaves key questions unanswered.