Amanda Peet and her husband, screenwriter David Benioff, weren't feeling very festive last Christmas. Their 10-month-old, Molly, had developed a horrible, hacking cough that spasmed through her body.

"We didn't know what it was," recalls the 2012 and The Whole Nine Yards star, 39, who's in Los Angeles to film the new NBC series Bent. "I would call my brother-in-law, who's an infectious disease specialist, and try to jam the phone up by her face as she was having a coughing fit." Finally, on Molly's fourth visit, her pediatrician decided to do a swab for pertussis (whooping cough), even though her symptoms didn't entirely fit the cold or flulike symptoms of this highly contagious respiratory tract infection.

The test came back positive. Baby Molly, who was too young to have received all the doses in the pertussis vaccine series, was the latest infant to develop the disease in what health experts call the largest whooping cough outbreak in California in decades. (A booster vaccine is now available for teens and adults to avoid passing the disease on to babies who haven't yet had all the shots.) More than 9,000 people in the state got pertussis in 2010, and at least 10 -- all infants under 3 months -- died.