Across the Philadelphia region, the rate of infections has held steady for the last five years — and cases are far less frequent here than in many other metro areas.
But that is not to say STDs aren't a serious issue locally. In Philadelphia, syphilis rates have gone up 30 percent since 2011, though other STDs have declined.
One theory for the overall increase: lack of money for public health programs.
"STD prevention resources across the nation are stretched thin, and we're beginning to see people slip through the public-health safety net," said Jonathan Mermin, the CDC's director of HIV/AIDs and STD Prevention, in a statement.
Nationwide, cases of syphilis, gonorrhea, and chlamydia have gone up more than 75 percent since 2011, growing from 46 million to nearly 75 million in 2015. All three are curable with antibiotics.
The rate of infection remains significantly lower than its World War II-era peak, but the recent spike worries public health officials.
"We have reached a decisive moment for the nation," said Mermin. "STD rates are rising, and many of the country's systems for preventing STDs have eroded. We must mobilize, rebuild, and expand services -- or the human and economic burden will continue to grow."
The highest rates of syphilis last year were reported in the Miami metro area (61 cases per 100,000 residents), New Orleans metro (60.5), and Atlanta metro (55), according to the CDC's new data. The mean for U.S. metropolitan areas was 31.4. The Philadelphia metro region reported about 23 cases per 100,000 people. The city of Philadelphia had 60 cases per 100,000, up 31 percent since 2011.
The three metro areas with the highest rates of gonorrhea last year were Milwaukee (236 cases per 100,000) and New Orleans and Memphis (both at 234). The mean was 137. The Philadelphia region recorded 161 cases per 100,000. The city of Philadelphia had 410 per 100,000, down 6.5 percent since 2011.
Chlamydia was most prevalent last year in the Memphis and New Orleans metro area (742 per 100,000), and Charlotte, N.C. (684). The mean was 495. The Philadelphia region reported 577 cases per 100,000 people. The city of Philadelphia had 1,265 cases per 100,000, down 6.3 percent..
Judith A. O'Donnell, chief of the department of infectious diseases at Penn Presbyterian Medical Center, said several factors were fueling the national growth in infections.
People ages 15 to 24 accounted for nearly two-thirds of chlamydia diagnoses and half of all those of gonorrhea.
"As each new generation becomes sexually active, you have to re-educate people about safer sex," O'Donnell said. "At the beginning of the HIV epidemic, the safer-sex message was well-adopted. Over the past 15 years, that message has gotten lost again. We don't talk about it much anymore."
Half of state and local STD programs have been hit by budget cuts, according to the CDC. Several states — Alabama, Arkansas, Indiana, Kansas, Louisiana, Ohio, and Utah — have slashed funding in recent years for Planned Parenthood, where large numbers of women have traditionally been educated about, and screened for, STDs.
"If you can't get messages to the community, you're going to have more transmission of the diseases," O'Donnell said.
O'Donnell praised Philadelphia's Department of Health for keeping the rate of STDs stable. She also credited the city's network of centers where people with little or no insurance coverage can get health care, and the dedicated STD clinic at Broad and Lombard Streets that provides confidential care to anyone who needs it.
The number of STDs in Philadelphia spiked in 2008, when kids as young as 16 were treated for four or five cases in succession.
"That was very common," said Caroline Johnson, director of the Health Department's division of disease control.
The city aggressively targeted teens on Facebook, Twitter and Instagram, pushing out information about condoms and where to get them free.
"We're still actively doing that," Johnson said Thursday. "It's a program that works."
According to the CDC's 2015 STD Surveillance Report, men who have sex with men accounted for the majority of new gonorrhea and syphilis cases. They also are more likely to be infected with antibiotic-resistant strains of gonorrhea.