Whooping Cough Epidemic in California as Cases Surge.

California’s whooping cough outbreak has reached epidemic levels, with 800 new cases in the last two weeks, according to the state’s public health agency.

There have been 3,458 cases of the respiratory infection, formally known as pertussis, in California as of June 10, the state’s Department of Public Health reported. That’s more than were reported in all of 2013. Most at risk are newborns, and two have died in California so far this year.

“Our biggest concern is always infants,” Stacey Martin, an epidemiologist with the U.S. Centers for Disease Control and Prevention’s division of bacterial diseases, said in a telephone interview. “There’s a gap in coverage between birth and the first vaccine.”

Whooping cough carries different symptoms at different ages. For children, a case can begin with a cough and runny nose before the cough worsens, characterized by a whooping sound that gives the disease its nickname. Infants don’t always have a cough but their faces may turn red or purple.

More than 900 of California’s cases occurred in April and May, a fivefold increase on the typical number seen in non-peak years, said Corey Egel, a spokesman for state health department.

The high number of cases isn’t unexpected because of the cyclical nature of the disease. California last had a widespread outbreak, or “peak,” in 2010. Martin said the priority is to encourage pregnant women to get the vaccine for pertussis, which the CDC has recommended since 2013.

Vaccinating pregnant women and infants helps prevent the spread of the disease, Ron Chapman, the state’s health department director, said yesterday in a statement.

The CDC recommends infants be vaccinated as early as six weeks after birth, because the effect of a vaccination given to their mother during pregnancy soon wears off, Martin said. The CDC also suggests shots for those spending time with newborns.

Nationwide, there have been three other deaths reported from whooping cough this year, Martin said. In total, 9,964 cases of whooping cough were reported in the U.S. through June 8, compared with 7,573 at the same time last year, the CDC said.

To contact the reporter on this story: Marie French in New York at mfrench25@bloomberg.net

To contact the editors responsible for this story: Reg Gale at rgale5@bloomberg.net Drew Armstrong, Andrew Pollack