Reported cases of whooping cough have tripled since last year, according to state health officials, with the Central Valley, the San Francisco Bay Area and the Los Angeles region seeing sizable increases in patients.

In California, there have been 584 cases of whooping cough, also known as pertussis, confirmed between Jan. 1 and May 31. That is three times as many cases as during the same time period last year, when 190 cases were confirmed, according to Ken August, a spokesman for the state's Department of Public Health.

The illness can cause adults to experience severe spasms of coughing that, if left untreated, can last three or four months. Infants are most vulnerable, as infection can cause death.

In the nine-county San Francisco Bay Area, there has been a six-fold hike, from 29 cases to 173 cases for the first five months of the year. In Fresno County, there are 76 cases so far this year, up from 9.

Los Angeles County reported 121 suspected and confirmed cases so far this year — more than half of them in May — up from 56 confirmed cases in the same period last year. In Orange County, there are 41 suspected and confirmed cases so far this year, up from six.

Health officials have warned physicians that doctors often mistake pertussis for another illness, causing a delay in diagnosis that can lead a patient to become sicker and infect an infant.

They urge anyone who will be in contact with infants, particularly mothers, fathers, grandparents and siblings, to get a pertussis booster shot. The strategy, called "cocooning," protects infants too young to be vaccinated by inoculating everyone around them.

Although many people were inoculated against whooping cough as children, the vaccine's effectiveness can begin to fade five years after it is given. Although inoculations have been available for children for decades, a pertussis booster shot for adults and adolescents, known as Tdap, became available only in 2005.

Five infants — all younger than three months — have died from whooping cough in California this year, exceeding the total from last year, when three infants died. Los Angeles County and the Central Valley reported two deaths each, while San Bernardino County has reported one death.

California is one of 11 states that does not require whooping cough booster shots for middle school students, along with Delaware, Georgia, Hawaii, Idaho, Iowa, Maine, Maryland, Mississippi, South Dakota and West Virginia.

ron.lin@latimes.com