Prevalence of several common sexually transmitted diseases (STDs) is on the increase in the commonwealth of Pennsylvania and throughout the United States. In fact, for the fourth straight year, the U.S. saw an increase in the combined rates of chlamydia, gonorrhea, and primary and secondary syphilis after the rates declining or remaining stable for many years.

Which STDs are most prevalent in Pennsylvania, where in our commonwealth are rates of certain diseases highest and how have STD rates changed here over time? To answer those questions, we’ll look at data from the federal Centers for Disease Control and Prevention and the Pennsylvania Department of Health.

Chlamydia Rates in Pennsylvania

Pennsylvania ranked ninth out of all states in sheer numbers of chlamydia infections in 2017, but after adjusting for population size, the commonwealth drops to near the bottom of the list.

Chlamydia infections per 100,000 people

Alaska 799.8
Louisiana 742.4
Mississippi 707.6
New Mexico 651.6
South Carolina 649.8
Georgia 631.4
North Carolina 619.7
Alabama 615.5
New York 591.6
Illinois 589.9
Total 528.8
Pennsylvania 441.5
Massachusetts 430.4
Minnesota 426.4
New Jersey 394
Idaho 368.4
Wyoming 365.8
Maine 342.1
Utah 332.2
New Hampshire 330.5
Vermont 297.5
West Virginia 226.1

Though Pennsylvania’s chlamydia rate is relatively low, the rate has risen by nearly 40% since 2003.

Pennsylvania chlamydia rate by year (cases per 100,000 people)

2003 301.6
2004 306.5
2005 299.8
2006 317.4
2007 341.6
2008 339.3
2009 341.7
2010 374.1
2011 415
2012 430.9
2013 407.5
2014 395.2
2015 417.6
2016 445.4
2017 441.5

Pennsylvania ranks in the top half of all Northeastern states for its chlamydia infection rate.

Chlamydia infection rate, Northeastern states (cases per 100,000 people)

New York 591.6
Rhode Island 500
Connecticut 496.3
Pennsylvania 441.5
Massachusetts 430.4
New Jersey 394
Maine 342.1
New Hampshire 330.5
Vermont 297.5

Gonorrhea Rates in Pennsylvania

Pennsylvania had the 10th most gonorrhea infections of any state in 2017, but the commonwealth ranks in the bottom half when considering the population-adjusted rate.

Gonorrhea infections per 100,000 people, top 25

Mississippi 309.8
Alaska 295.1
Louisiana 256.7
South Carolina 254.4
Alabama 245.7
Oklahoma 231.4
North Carolina 225.4
Arkansas 224.5
Georgia 219.8
New Mexico 215.7
Total 171.9
Pennsylvania 119.2
Rhode Island 102.9
Hawaii 95.1
Utah 83.3
Montana 75
West Virginia 70.8
Wyoming 70.4
Idaho 58.6
Maine 46.6
New Hampshire 38.4
Vermont 32.5

Gonorrhea rates have risen all over the country, but Pennsylvania has seen a much more modest increase than some other places. For instance, Wyoming’s gonorrhea rate has exploded by 523% since 2013, while Pennsylvania's rate went up only about 10% in that time. However, the commonwealth’s rate is up significantly since a 21st-century low in 2009.

Pennsylvania gonorrhea rate by year (cases per 100,000 people)

2003 96
2004 90.6
2005 90.3
2006 92.2
2007 102.2
2008 88.9
2009 80.4
2010 101.4
2011 108.1
2012 120.6
2013 108.6
2014 99.4
2015 99.9
2016 114.3
2017 119.2

Pennsylvania has the second-highest prevalence of gonorrhea among Northeastern states, though it’s far behind regional leader New York.

Gonorrhea infection rate, Northeastern states (cases per 100,000 people)

New York 172.7
Pennsylvania 119.2
Massachusetts 113.6
Connecticut 109.4
New Jersey 105.5
Rhode Island 102.9
Maine 46.6
New Hampshire 38.4
Vermont 32.5

Syphilis Rates in Pennsylvania

Pennsylvania ranks close to the middle nationally when it comes to the rate of people newly diagnosed with primary or secondary syphilis, but the state comes in No. 10 in overall total cases. Still, the commonwealth’s syphilis rate is well below the national rate.

Primary and secondary syphilis infections per 100,000 people

Nevada 20
California 17.1
Louisiana 14.5
Georgia 14.4
Arizona 13.6
New York 11.9
Florida 11.6
North Carolina 11.2
Mississippi 10.4
Illinois 9.6
Total 9.5
Pennsylvania 6.2
South Dakota 3.8
West Virginia 3.4
Iowa 3.2
New Hampshire 3.2
Connecticut 3.1
Wisconsin 3
Nebraska 2.3
Vermont 2.1
Alaska 1.8
Wyoming 0.7

Pennsylvania’s rate of primary and secondary syphilis has surged in recent years, climbing 68% between 2013 and 2017 alone and going up by more than 500% since 2004.

Pennsylvania primary and secondary syphilis rate by year (cases per 100,000 people)

2003 1.3
2004 1
2005 1.6
2006 2.1
2007 2.1
2008 2.2
2009 2.7
2010 2.9
2011 2.9
2012 3.9
2013 3.7
2014 4.2
2015 5.1
2016 5.9
2017 6.2

Pennsylvania’s rate of primary and secondary syphilis is in the top half compared to regional neighbors.

Primary and secondary syphilis infection rates, Northeastern states (cases per 100,000 people)

New York 11.9
Massachusetts 7.9
Rhode Island 6.7
Pennsylvania 6.2
New Jersey 5.6
Maine 4.9
New Hampshire 3.2
Connecticut 3.1
Vermont 2.1

HIV & Other STD Rates in Pennsylvania


More than 1,000 people in Pennsylvania were newly diagnosed with HIV in 2017, though both the number and population-adjusted rate fell in the commonwealth between 2016 and 2017 with each dropping by around 5%. See How to Test for HIV

Hepatitis B & C

Rates of acute hepatitis B infections in Pennsylvania are among the lowest in the country, and the commonwealth has managed to steadily bring the rate down over the years, with a 40% decrease in the rate between 2013 and 2016. The story is different for acute Hepatitis C infections, though, as Pennsylvania ranks 11th overall and has a rate about 40% higher than the national rate. Additionally, the rate of acute hep C cases has surged by 260% since 2012. See How to Test for Hepatitis


Human papillomavirus is by far the most common STD in the world. It’s so common, in fact, that estimating in any given year how many people have contracted it is virtually impossible. But because HPV is the leading cause of several types of cancer, including cervical, penile and anal cancer, examining the rate of HPV-caused cancer cases in each state can help illustrate how prevalent untreated high-risk HPV is. In Pennsylvania, HPV-related cancer is diagnosed at a rate of 12.4 per 100,000 people, putting the commonwealth just over the national median of 11.7 per 100,000. See How to Test for HPV

STDs in Pennsylvania Cities & Counties

Looking at the commonwealth overall reveals just one portion of the full picture of sexual health in Pennsylvania. That’s because Pennsylvania is home to multiple metro areas that often carry more weight in health statistics. For instance, the Philadelphia metro area (which includes portions of Delaware and New Jersey) has the 10th highest chlamydia rate of any metro area in the country.


About a third of all chlamydia cases in Pennsylvania in 2017 were in people living in Philadelphia.

Pennsylvania counties by chlamydia infection rate (cases per 100,000 people)

Philadelphia 1,335.90
Dauphin 667
Sullivan 509.1
Centre 498
Delaware 495.7
Lehigh 461.4
Berks 451.1
Allegheny 427
Mifflin 411.7
Northampton 388.9


Philadelphia accounted for about 48% of all gonorrhea cases in Pennsylvania in 2017, and the Pittsburgh area added another 12%.

Pennsylvania counties by gonorrhea infection rate (cases per 100,000 people)

Philadelphia 461
Dauphin 206
Allegheny 146.7
Northampton 134.8
Erie 126.4
Delaware 124.7
Lehigh 116.2
Beaver 109.5
Mercer 98.4
Lawrence 90.7

Primary and secondary syphilis

More than half of the primary and secondary syphilis cases in Pennsylvania in 2017 were diagnosed in Philadelphia.

Pennsylvania counties by primary and secondary syphilis infection rate (cases per 100,000 people)

Philadelphia 29
Dauphin 10.5
Delaware 6.7
Pennsylvania 6.2
Cumberland 4.8
Allegheny 4.7
Lehigh 4.4
York 4.3
Montgomery 3.5
Lancaster 3.1


While most STDs have seen their prevalence rise over the past few years in the commonwealth of Pennsylvania, the reality is that most people here who have STDs probably don’t know about it. That’s because most STDs either don’t display symptoms or they have symptoms that are easily mistaken for other issues. The only way to know for sure that you are healthy and won’t pass along a potentially serious infection to your sexual partners is to get yourself tested for the STDs for which you’re most at risk.

Additional References

Note: The CDC publishes comprehensive STD data on only three of the many conditions that are sexually transmitted — chlamydia, gonorrhea, and primary and secondary syphilis. Many other STDs are not classified as nationally notifiable diseases, meaning states are not legally obligated to report infection rates. Also, while the CDC collects data for the District of Columbia, the population density of the district prevents it from being included in rankings.


by AtHomeSTDKit

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