Cases of the highly contagious bacterial disease whooping cough, or pertussis, have exploded in California over the last month, prompting health officials to announce a state-wide epidemic.

Ron Chapman, director of the California Department of Public Health, said in a news release that his agency has received reports of 3,458 instances of whooping cough since Jan. 1 -- already surpassing the number of known cases in all of 2013.

Actually, the incidence rate of whooping cough tends to be cyclical, peaking every 3-5 years. That said, last peak in the Golden State occurred in 2010, so another spike in occurrences is likely underway.

"Preventing severe disease and death in infants is our highest priority," said Chapman. "We urge all pregnant women to get vaccinated. We also urge parents to vaccinate infants as soon as possible."

Infants who are too young to be fully immunized are most vulnerable to the sometimes fatal disease.

According to state statistics, two-thirds of whooping cough hospitalizations have been in children four months or younger. Two infant deaths have been reported.

The Tdap vaccination for pregnant women "is the best way to protect infants who are too young to be vaccinated. All pregnant women should be vaccinated with Tdap in the third trimester of each pregnancy, regardless of previous Tdap vaccination," department officials said in the release. "In addition, infants should be vaccinated as soon as possible. The first dose of pertussis vaccine can be given as early as 6 weeks of age."

Current recommendations say older children, pre-adolescents and adults should also receive vaccinations against the disease, particularly if they spend time around newborn babies.

"Unlike some other vaccine-preventable diseases, like measles, neither vaccination nor illness from pertussis offers lifetime immunity," Chapman said. "However, vaccination is still the best defense against this potentially fatal disease."

The symptoms of whooping cough vary by age, although a typical case in children generally starts with a cough and runny nose for one to two weeks.

The cough may then worsen, with the infected children suffering rapid bouts of coughing that end with a "whooping" sound.

Young infants may not demonstrate typical pertussis symptoms and may not even have any apparent cough, although parents have described episodes where an infant's face turns red or purple.

With infected adults, pertussis may simply be a cough that persists for several weeks.