California health officials say a tenth baby has died of whooping cough in the state's worst epidemic in 55 years.
The 6-week-old baby died last week after being treated at Rady Children's Hospital in San Diego.
More than 5,270 cases of the highly-contagious illness have been reported in California this year. The previous record was set in 1955 when there were 4,949 cases reported.
All of the babies who have died were too young to be fully immunized against the disease, according to health officials.
Whooping cough is a highly contagious, cyclical illness that peaks in number of infections every five years.
The last peak occurred in 2005 when California reported 3,182 cases, with 574 hospitalizations and seven deaths.
The prevalence of the disease, also known as pertussis, peaks in the summer months, according to Al Lundeen, a spokesman for the state Department of Health, but reporting lags make it difficult to determine if the peak has passed.
Jonathan Fielding, the county's health director, urges parents and caretakers to get vaccinations to avoid any more deaths.
Most kids get five doses of the vaccine DTaP before kindergarten to prevent whooping cough, but those vaccines don't immunize them for life.
Health officials say most kids are once again susceptible to the disease by middle school.
A booster dose of the vaccine is recommended for people between the ages of 11 and 18, as well as for people who have contact with infants.
A typical case starts with a cough and runny nose for one to two weeks, followed by weeks or months of rapid coughing fits that sometimes end with a whooping sound.

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