Syphilis Facts and Statistics: What You Need to Know

Despite the availability of effective treatments and previously effective public health strategies, there has been a resurgence of syphilis in the United States. Syphilis is a sexually transmitted bacterial infection.

In 2020, the Centers for Disease Control and Prevention (CDC) reported 133,945 cases of this syphilis, most of which occurred among men who have sex with men (MSM).

But, MSM wasn't the only group affected. Rates are also rising among heterosexual people. Females, particularly younger females in their childbearing years, also experienced a rise in new infections, coinciding with an increase in the number of congenital syphilis cases (present at birth in the newborn).

This article looks at current syphilis statistics in the United States, including the various factors contributing to the resurgence of this all-too-common sexually transmitted infection (STI).

Syphilis Overview

Syphilis is an STI caused by the bacteria Treponema pallidum. It is typically spread through sexual contact but can also be passed from mother to child during pregnancy, resulting in congenital syphilis.

Syphilis can cause different symptoms based on the stage of infection:

• Primary syphilis can occur 10 days to three months after sexual contact, manifesting with a painless genital ulcer known as a chancre.
• Secondary syphilis occurs two weeks to six months after the ulcer heals, during which various symptoms may develop. These include fever, swollen lymph nodes, rash (which may be widespread and/or involve the palms and soles), patchy hair loss (alopecia), and warty growths called condyloma lata.
• Latent syphilis is the period in which syphilis persists with no symptoms.
• Tertiary syphilis is the most advanced and severe stage of infection that typically occurs within 20 years of the initial infection, causing a cascade of symptoms affecting the brain, heart, liver, eyes, and other organ systems.

For all stages of infections, penicillins are the treatment of choice. This includes benzathine penicillin for primary and secondary syphilis and penicillin G for tertiary syphilis. Other classes of antibiotics may be used if penicillin is not an option (such as due to allergy).

Syphilis is diagnosed with blood tests. In people with neurosyphilis (a complication that can occur at any stage), the infection can be diagnosed by evaluating cerebrospinal fluid obtained by a spinal tap.

How Syphilis Is Transmitted

Treponema pallidum, the bacteria that causes syphilis, only exists in humans. It is unlike other Treponema bacteria in that it can enter the body through intact mucous membranes of the mouth, vagina, and rectum. It can also penetrate the blood-brain barrier and invade the central nervous system.

Because of this, syphilis can be easily passed from one person to the next through oral, vaginal, and anal sex. Transmission of T. pallidum involves direct contact with a chancre sore (which may not always be visible if it is beneath the foreskin or in the vagina, mouth, or rectum).

Syphilis can also be passed vertically during pregnancy (from the pregnant person to the fetus). Even so, this is less common in the United States due to routine prenatal STI screening of pregnant people.

You cannot get syphilis through toilet seats, doorknobs, bathtubs, swimming pools, hot tubs, shared utensils, or shared clothes. This is because the bacterium dies very quickly once outside of the body.

Neither kissing nor the shared use of needles are considered a viable means of transmission.

How Common Is Syphilis?

Of the eight most common STIs⁠ in the United States—chlamydia, genital herpes, gonorrhea, hepatitis B, HIV, human papillomavirus (HPV), syphilis, and trichomoniasis—syphilis ranks seventh overall in terms of annual new infections.

 Since reaching a historic low in 2001, the rate of primary and secondary syphilis has increased nearly every year. In 2020, 133,945 cases of syphilis were reported, of which 41,655 were primary and secondary syphilis.

Men who have sex with men (MSM) account for the lion's share of new primary and secondary syphilis infections.

In 2020, the distribution of cases broke down as follows:

• Men who have sex with men only: 42% (16,231 cases)
• Men who have sex with women only: 19% (7,289 cases)
• Men whose sex partner is of unknown sex: 17% (6.732 cases)
• Women: 17% (6,493 cases)
  
• Men who have sex with men and women: 6% (2,150 cases)

Despite being disproportionately affected, MSM experienced a 2.2% drop in new primary and secondary infections in the latest CDC survey. During the same period, the rate increased by 21% among females.

Syphilis by Race/Ethnicity

As with most infectious diseases, syphilis affects some racial or ethnic groups more than others. This is especially true of Black, Latinx, and Native American people in the United States.

These groups are vulnerable to STIs due to risk factors like poverty, institutional racism, health care discrimination, or simply living in a community where high STI rates increase the odds of infection.

For primary and secondary syphilis, these factors translate to disproportionately high infection rates among different communities. According to CDC statistics:

• Black people are five times more likely to get syphilis than White people.
• Native Americans and Alaska Natives are three times more likely to get syphilis than White people.
• Latinx people are two times more likely to get syphilis than White people.

Of all racial or ethnic groups, only Asians are around 30% less likely to get syphilis than Whites.

Syphilis by Age and Gender

Because syphilis is mainly transmitted through sex, the disease is far more common in younger people who tend to be more sexually active.

The latest CDC statistics show that the annual rate of primary and secondary syphilis for all age groups is roughly 13 per 100,000 people. This means that for every 100,000 people living in the United States, 13 will get newly infected with syphilis each year.

Among adults 25 to 29, the rate is nearly three times higher (at 35 cases per 100,000), while the rate in males 25 to 29 is nearly five times higher (at 58 cases per 100,000).

In 2020, the numbers of new primary and secondary syphilis infections broken down by age and biological sex were as follows:

Although the rate of infection is lower in females than in males, it has increased by 147% from 2016 to 2020. This suggests that the syphilis epidemic among heterosexuals is increasing at a faster pace than MSM.

Congenital Syphilis

While congenital syphilis has become less common in the United States, it still occurs. With the rise in syphilis infections among females of reproductive age, public health officials have also seen an uptick in congenital syphilis cases since 2013.

As with adult infections, the rate of congenital syphilis is dramatically higher in communities of color. According to CDC statistics:

• Latinx people are three times more likely to experience congenital syphilis than White people.
• Black people are five times more likely to experience congenital syphilis than White people.
• Native Americans or Alaska Natives are six times more likely to experience congenital syphilis than White people.
• Native Hawaiians and other Pacific Islanders are also six times more likely to experience congenital syphilis than White people.

Causes of Syphilis and Risk Factors

Oral, vaginal, and anal sex remain the primary modes of transmission of syphilis. Infection occurs as a result of direct contact with a chancre.

The sexual risk factors for syphilis include:

• Engaging in condomless oral, vaginal, or anal sex
• Having multiple sex partners
• Being a gay or bisexual man
• Having HIV (which is linked to an increased risk of repeated syphilis)
• Having sex while using recreational drugs

Some of these risk factors overlap with those of congenital syphilis, including:

• Having multiple sex partners
• Having sex with recreational drug use
• Housing insecurity or homelessness
• Late entry into prenatal care or no prenatal care
• Transactional sex (sex for money)

What Are the Mortality Rates for Syphilis?

Before the widespread use of penicillin, syphilis was a major cause of death and disability worldwide. During the 1920s, syphilis was the 10th leading cause of death in the United States, with a mortality rate of around 11%.

Since that time, mortality rates have dropped dramatically, with only around 6,500 syphilis-related deaths occurring between 1968 to 2015.

Today, death from syphilis is rare in the United States, even during the most advanced stages of infection.

The deaths that do occur are largely the result of congenital syphilis. In 2020 alone, the CDC reported 149 deaths out of 2,148  cases of congenital syphilis, translating to a 1-in-14 risk of death.

Screening and Early Detection

Syphilis is often referred to as the "great pretender" because its symptoms are easily confused with other diseases. Blood tests are ultimately needed to confirm the diagnosis. Testing can also help determine if the infection is recent or occurred in the past.

While testing is commonly performed when symptoms appear, certain groups may benefit from routine screening, given the effectiveness of penicillin treatment (and the potential harms of non-treatment).

The CDC currently recommends syphilis screening for anyone without symptoms who is at an increased risk of infection, including:

• Men who have sex with men: Testing is recommended annually for sexually active MSM and every three to six months for those at high risk.
  
• Men who have sex with women: Testing is recommended for asymptomatic males who are at an increased risk of infection.
• Women: Testing is recommended for asymptomatic females who are at an increased risk of infection.
• Pregnant people: Testing is recommended at the first prenatal visit and again at 28 weeks of pregnancy.
• People with HIV: Testing is recommended at the first HIV evaluation and every year after that if sexually active. Individuals at high risk may need more frequent screening.
• Transgender people: Consider screening annually based on sexual behaviors and individual risk factors.
  

Summary

Syphilis is the seventh most common sexually transmitted infection (STI) in the United States in terms of new infections. In 2020, a total of 133,945 cases were reported, 43% of which occurred in men who have sex with men (MSM).

Although MSM accounts for the lion's share of new infections, syphilis infections among women have risen at a far faster rate in recent years in tandem with a rise in the number of congenital syphilis cases.

As with other common STIs, syphilis disproportionately affects Black, Latinx, and Native American people due to intersecting risk factors like poverty, health care discrimination, and high rates of STIs in economically disadvantaged communities.