It is by far the most-reported sexually transmitted disease in the Tampa Bay area and all across the United States.
The numbers keep rising, but health officials say many more people have chlamydia than even the statistics indicate. They just don't know it yet.
The Centers for Disease Control and Prevention calls chlamydia a "silent" disease, because in most cases there are no symptoms.
"Of course, if you don't have signs or symptoms, what are the chances you're going to be tested?" said Sherry Lewis, the STD program manager for Pinellas and Pasco counties. "A lot of individuals don't know they have it."
More than 1.1 million cases were reported to the centers in 2007, a 7.5 percent increase in a single year and the largest number ever reported to the agency for any condition that it tracks.
Chlamydia is considered a reportable disease, one that must be reported to government health officials when diagnosed. Others include tuberculosis, AIDS, mumps and cholera. Of all reportable diseases, chlamydia is the most common.
Locally, there were 6,127 reported cases in Hillsborough County, 3,878 in Pinellas and 711 in Pasco in 2008, according to provisional health department figures. The numbers represent double-digit percentage increases from 2007. In Hernando, with 279 cases, the number actually decreased slightly, but with such a small sample size that it could be a quirk.
Chlamydia is caused by the bacterium Chlamydia trachomatis, which can damage a woman's reproductive organs if not caught early, and cause pain, burning and swelling in male reproductive organs. It can be transmitted during vaginal, anal or oral sex, and can also be passed from mother to baby during vaginal childbirth. Chlamydia can be cured with antibiotics — if it is detected.
Local health officials say the increase in chlamydia rates is due largely to more screening, increased community outreach and education, and a new way to test people — through urine, instead of the more invasive swab method. But the Centers for Disease Control says the statistics may also reflect a true increase in the number of cases.
In Pinellas, the 3,878 chlamydia cases reported in 2008 more than doubled the next-highest reportable disease, hepatitis C. In Hillsborough, chlamydia far outnumbered gonorrhea cases.
So, why is there so much chlamydia?
"That's a question we've been asking ourselves for a long time," said Wendell Evans, interim program manager for sexually transmitted diseases in Hillsborough County.
Evans said one possible reason is that not enough men are being treated. The rate of reported infection among women is nearly three times as high as for men, and that could mean that there are lots of men unknowingly spreading the disease, he said.
Both Pinellas and Hillsborough officials say outreach and education are key to getting more people tested and treated for venereal diseases.
Lewis said Pinellas officials give presentations in middle schools and high schools. "That's where it starts, because of the peer pressure," she said.
Chlamydia rates are highest among people aged 15-24, constituting more than 70 percent of reported cases in Pinellas and Hillsborough in 2008. There were also 86 cases in the two counties involving children ages 10-14.
Blacks made up about half of reported chlamydia cases in Pinellas and Hillsborough in 2008. Evans said Hillsborough officials target high-risk areas, such as predominantly African-American neighborhoods, for more outreach and testing.
Lewis, however, is quick to say that it's not just people who fall into the high-incidence categories that should be concerned.
"Anyone who is sexually active should get tested," she said.
Times researcher Connie Humburg contributed to this report. Richard Martin can be reached at firstname.lastname@example.org or (727) 893-8330.