The majority of these new diagnoses (1.6 million) were cases of chlamydia, according to the annual Sexually Transmitted Disease Surveillance Report by the US Centers for Disease Control and Prevention (CDC).
There were also 470,000 gonorrhoea cases and almost 28,000 cases of primary and secondary syphilis - the most infectious stages of the disease, the report said.
While all three of these STDs can be cured with antibiotics, if left undiagnosed and untreated, they can have serious health consequences, including infertility, life- threatening ectopic pregnancy, stillbirth in infants, and increased risk for HIV transmission, researchers said.
"STDs are a persistent enemy, growing in number, and outpacing our ability to respond," said Mermin.
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While young women continue to bear the greatest burden of chlamydia (nearly half of all diagnosed infections), surges in syphilis and gonorrhoea are increasingly affecting new populations, the report said.
Syphilis rates increased by nearly 18 per cent overall from 2015 to 2016. The majority of these cases occur among men - especially gay, bisexual and other men who have sex with men (MSM), it said.
More than 600 cases of congenital syphilis were reported in 2016, which has resulted in more than 40 deaths and severe health complications among newborns.
The disease is preventable through routine screening and timely treatment for syphilis among pregnant women.
"Every baby born with syphilis represents a tragic systems failure," said Gail Bolan, director of CDC's Division of STD Prevention.
"All it takes is a simple STD test and antibiotic treatment to prevent this enormous heartache and help assure a healthy start for the next generation of Americans," said Bolan.
These trends are particularly alarming in light of the growing threat of drug resistance to the last remaining recommended gonorrhoea treatment.
MSM also bear a great syphilis burden. MSM make up a majority of syphilis cases, and half of MSM diagnosed with syphilis were also living with HIV - pointing to the need to integrate STD and HIV prevention and care services, the report said.