Gonorrhea is caused by the bacterium Neisseria gonorrhoeae, a highly specialized germ that infects the moist mucous membranes of the human body. It spreads through vaginal, anal, or oral sex without a condom, and a pregnant person can pass it to their baby during childbirth. With over 543,000 cases reported in the United States in 2024 alone, it remains one of the most common sexually transmitted infections in the country.
The Bacterium Behind Gonorrhea
Neisseria gonorrhoeae is a tiny, kidney bean-shaped bacterium, roughly 0.6 to 1.0 micrometers across. Under a microscope it appears in pairs, with adjacent sides flattened against each other like two coffee beans pressed together. It cannot survive long outside the human body. It doesn’t form protective spores, it can’t move on its own, and it requires oxygen to live. These limitations are why gonorrhea spreads only through close, direct contact with infected mucous membranes rather than through surfaces, water, or air.
What the bacterium lacks in environmental toughness it makes up for in its ability to evade the immune system. Its outer membrane is studded with hair-like projections called pili that latch onto human cells with high affinity. Special surface proteins help it dodge the body’s first-line immune defenders, the white blood cells that would normally engulf and destroy an invader. This combination of strong attachment and immune evasion is what makes the infection so effective at establishing itself.
How the Bacteria Infect the Body
Once Neisseria gonorrhoeae reaches a mucosal surface, it follows a stepwise process. It first binds tightly to the lining cells using its pili, preferentially targeting non-ciliated cells (the cells without the tiny sweeping hairs that help clear mucus). Within about 20 minutes of contact, the bacteria can be pulled inside these cells. They then travel through the cell from top to bottom, a process called transcytosis, emerging on the other side into the tissue beneath the surface lining.
The bacteria can also multiply on the outside of mucosal surfaces without ever entering a cell, and they have backup adhesion methods beyond their pili. This redundancy makes the infection difficult for the body to prevent once exposure occurs. The resulting immune response, a flood of white blood cells to the infected area, produces the characteristic discharge and inflammation associated with gonorrhea symptoms.
How Gonorrhea Spreads
Gonorrhea passes from person to person during sexual contact. Vaginal, anal, and oral sex can all transmit the infection. The bacterium thrives on the warm, moist lining of the reproductive tract, rectum, and throat, so any unprotected contact with these areas carries risk. Ejaculation does not have to occur for transmission to happen.
Mother-to-child transmission is the other established route. A pregnant person with an active gonorrhea infection can pass the bacteria to their baby as it moves through the birth canal. In newborns, this typically causes a serious eye infection that can lead to blindness if untreated, which is why hospitals routinely apply antibiotic eye drops to newborns shortly after delivery.
Where It Infects
Most people think of gonorrhea as a genital infection, and that is the most common presentation. But the bacteria can establish themselves in several areas of the body depending on the type of sexual contact involved.
- Genitals: The urethra in men and the cervix in women are the primary sites. Symptoms include painful urination and unusual discharge.
- Rectum: Anal sex can lead to rectal infection, causing itching, discharge, and pain during bowel movements.
- Throat: Oral sex can result in pharyngeal gonorrhea, which may cause a sore or scratchy throat and difficulty swallowing, though it often produces no symptoms at all.
- Eyes: Primarily a concern for newborns during delivery, though adults can transfer the bacteria to their eyes through contaminated hands.
Throat and rectal infections are less common than genital infections, but they are also more likely to go unnoticed because they often cause mild or no symptoms. This makes them an important, often overlooked source of ongoing transmission.
What Happens If It Goes Untreated
Left alone, gonorrhea doesn’t just stay put. In women, the bacteria can travel upward from the cervix into the uterus and fallopian tubes, causing pelvic inflammatory disease. This can lead to chronic pelvic pain, scarring of the reproductive organs, and infertility. Ectopic pregnancies, where a fertilized egg implants outside the uterus, become more likely after fallopian tube damage.
In men, untreated gonorrhea can spread to the epididymis, the coiled tube behind each testicle, causing painful swelling that in rare cases affects fertility. In anyone, the infection can enter the bloodstream and spread throughout the body, a condition called disseminated gonococcal infection. This can cause swollen and painful joints, liver inflammation, and in severe cases, damage to heart valves and the brain.
How It’s Detected
The standard test for gonorrhea is a nucleic acid amplification test, or NAAT, which detects the bacterium’s genetic material. NAATs are the preferred method because they are both highly sensitive (catching more than 90% of infections) and highly specific (with accuracy above 99%, meaning false positives are rare). Testing typically involves a urine sample or a swab from the infected site.
For men with obvious urethral symptoms, a simple microscope examination of the discharge can confirm the diagnosis on the spot by revealing the characteristic paired bacteria inside white blood cells. This approach is less reliable in people without symptoms and isn’t useful for throat or rectal infections, where NAATs are the better choice. Bacterial culture, the older method of growing the organism in a lab, is now primarily reserved for cases where treatment fails and doctors need to check which antibiotics the strain is still vulnerable to.
Why Antibiotic Resistance Matters
Neisseria gonorrhoeae has a remarkable track record of developing resistance to antibiotics. Over the decades it has rendered sulfonamides, penicillin, tetracycline, and fluoroquinolones largely ineffective. Current treatment relies on a single remaining first-line antibiotic class, and resistance to it has been documented in several countries. This is why culture-based testing remains essential for treatment failures: it lets labs determine exactly which drugs still work against a given strain.
The practical consequence for patients is that follow-up matters. If symptoms persist after treatment, retesting with a culture is important to confirm the infection has cleared. Reinfection is also common, since having gonorrhea once does not create lasting immunity, so repeat testing a few months after treatment is generally recommended for anyone who has been treated.
Who Gets Gonorrhea
In the United States, provisional 2024 data show 543,409 reported gonorrhea cases, a 10% decline from the prior year and the third consecutive annual drop. Men account for roughly 63% of reported cases, with a rate of 203 per 100,000 people compared to 116 per 100,000 among women. The higher rate in men partly reflects the disproportionate burden among men who have sex with men, though gonorrhea affects people across all demographics.
These numbers almost certainly undercount the true burden. Many infections, particularly in the throat and rectum, produce no symptoms and are never tested for. Asymptomatic genital infections are also common, especially in women, where up to half of cases may go unnoticed. Every undiagnosed case is a potential source of further transmission and a ticking clock for complications.