The California Department of Public Health says more than 6,200 Californians have been infected with whooping cough in the largest epidemic to strike the state since 1950.
Updated totals released by the department show that as of late Tuesday there were 6,257 cases of whooping cough, an increase of 279 cases from last week.
Ten deaths have been reported, all infants younger than three months.
The highly contagious illness has symptoms similar to the common cold, but a persistent cough that lasts weeks may indicate the illness, which is also known as pertussis.
All the babies who have died this year were too young to be fully immunized, so health officials are urging parents and caretakers to get booster shots to create a cocoon of immunity around vulnerable children.