Los Angeles County has already logged 345 confirmed and probable cases of pertussis this year, health officials said Thursday.
The county's Department of Public Health is also investigating 356 "suspect cases" of the contagious and potentially deadly illness, also known as whooping cough, the department reported in a statement.
"We are asking residents to make certain that everyone in your family has been vaccinated to help stop the spread of pertussis," said department director Dr. Jonathan Fielding. "Being vaccinated protects your family and reduces the chance that pertussis will spread to our most vulnerable residents -- infants who are too young to be fully vaccinated."
Whooping cough -- which causes cold-like symptoms that can escalate into severe coughing fits strong enough to induce vomiting and break ribs -- can strike people of all ages. It is particularly dangerous in infants, Fielding said.
About half of infants who get pertussis require hospitalization, and three infants in California have died from the disease thus far this year, according to the county health department release.
The rise in cases in L.A. County, where a number of elementary, middle, and high school students have fallen ill, mirrors a statewide uptick in the disease. On June 13, the California Department of Public Health declared an epidemic in the state. As of June 10, there had been 3,458 cases of pertussis reported in 2014 -- more than 800 in the preceding two weeks.
Pertussis cases rise and fall over a three- to 5-year cycle. Since California's last peak occurred in 2010, it is likely another cyclical peak is occurring, the state health department said.
The U.S. Centers for Disease Control and Prevention recommends doses of the pertussis vaccine at 2, 4 and 6 months; between 15 and 18 months; and between 4 and 6 years. It also calls for a booster dose at 11 to 12 years, and for booster doses in some adults, including pregnant women.
L.A.'s 2014 whooping cough case count through June 23 exceeds the total tally of whooping cough cases in the county in 2012 and in 2013, the health department noted. Throughout the entire year of 2012, Los Angeles County had 295 confirmed and probable cases of the illness.
In 2013, that number rose to 295 cases.