Is It the Flu or an STI?

If you have flu-like symptoms, it could be from the flu (influenza), a similar viral illness, or a sexually transmitted infection (STI), also called a sexually transmitted disease (STD).

STIs are transmitted through direct contact, usually (but not always) sexual in nature. Many exist, and each has unique symptoms. Common STIs that cause flu-like symptoms include:

• Gonorrhea and throat gonorrhea
• Hepatitis B
• Herpes
• Human immunodeficiency virus (HIV)/AIDS
• Syphilis

This article will review flu-like symptoms and list the STIs that can cause them. It will also detail other STI symptoms and explain how to tell the difference between the flu and STIs.

Flu-Like STI Symptoms

The flu is a respiratory illness caused by the influenza virus. Influenza A and influenza B are common types of influenza that share many of the same symptoms. Primary flu symptoms include cough, sore throat, and nasal congestion (runny nose). Flu symptoms that are shared by STIs include:

• Fever
• Nausea and vomiting
• Headaches or body aches
• Fatigue
• Sore throat
• Swollen lymph nodes (glands)

Fever

A fever is a common sign of illness. Much of the time, it comes from the immune response to infection—your body tries to kill the invading pathogen with heat.

STIs that may cause fever when you’re first infected include:

• Hepatitis B
• Herpes
• HIV/AIDS
• Syphilis

Gonorrhea itself doesn’t cause a fever. However, if it is left untreated, it can lead to pelvic inflammatory disease (PID), which may cause a fever.

Nausea and Vomiting

Nausea (upset stomach) and vomiting aren’t common flu symptoms, especially in adults, but they can occur. STIs that cause these symptoms include:

• Hepatitis B
• HIV/AIDS
• Syphilis

Headaches/Body Aches

Many common illnesses, including the flu, can cause headaches and general body aches. Again, this is from the immune system’s response. It sends white blood cells to fight the virus or bacterium, and that leads to inflammation.

STIs that cause headaches and body aches symptoms are:

• Herpes
• HIV/AIDS
• Syphilis

Fatigue

Fatigue also comes from the immune response to illness. It takes a lot of your body’s resources to fight off pathogens. Fatigue is common in:

• Hepatitis B
• Herpes
• HIV/AIDS
• Syphilis

Sore Throat

A sore throat is a common symptom of the flu and many other infections. It’s caused directly by viruses or bacteria, which can irritate the back of your throat (pharynx). STIs associated with a sore throat are:

• HIV/AIDS
• Syphilis

With oral sex, it’s possible to catch gonorrhea in your throat. This generally causes a sore throat.

Swollen Lymph Nodes

Sometimes referred to as “glands,” lymph nodes are in many places throughout your body, including the:

• Neck
• Armpit
• Chest
• Abdomen
• Groin

Lymph nodes contain specialized immune cells that fight disease. Almost any infectious illness can cause them to swell.

STIs that can cause swollen lymph nodes include:

• Gonorrhea of the throat
• Hepatitis B
• Herpes
• HIV/AIDS
• Syphilis
  

Other STI Symptoms

When you’re trying to figure out which STI you could have, you’ll likely need to look beyond flu-like symptoms. Each STI has its own set of other signs and symptoms.

Gonorrhea (Reproductive Organs/Urethra)

Gonorrhea is caused by a bacterial infection. It affects the female reproductive organs, urethra, rectum, and sometimes other areas of the body. Oral sex can cause a throat infection.

Many people with gonorrhea, especially males, have no symptoms or have symptoms that are very mild. 

With an infection of the female reproductive organs, symptoms may include:

• Painful urination
• Increased vaginal discharge
• Bleeding between periods

If gonorrhea is left untreated, it may develop into pelvic inflammatory disease (PID). Symptoms may include:

• Chronic pelvic pain
• Abscesses
• Fallopian tube damage

The damage to the fallopian tubes can cause infertility or ectopic pregnancy (when the fetus implants outside of the uterus).

For males with gonorrhea infection in the urethra (tube in the penis that urine passes through), symptoms may include:

• Painful urination
• White, yellow, or green discharge
• Less often, pain in the testicles or scrotum

People of any sex may also experience rectal symptoms of gonorrhea. These may include anal discharge, itching, bleeding, and soreness.

Hepatitis B

Hepatitis B is a viral liver disease that can be transmitted through sex. In addition to flu-like symptoms, it may also cause:

• Loss of appetite
• Abdominal pain
• Dark urine
• Clay-colored stool
• Joint pain
• Jaundice (yellow skin)

Some people with hepatitis B eventually develop chronic liver disease. A vaccine is available to help prevent hepatitis B.

Herpes

Herpes is an incurable (but treatable) STI caused by a virus. It comes in two forms: genital (simplex 2) and oral (simplex 1). Sores in either location can spread the virus to the genitals through skin-to-skin contact.

Flu-like symptoms are often the first signs of herpes infection. They may be accompanied by: 

• An itchy or tingly feeling and possibly a small swollen patch that may be discolored
• One or more small blisters may form on the patch
• Blisters that break open and turn into painful sores that scab and heal over between two and six weeks

The first outbreak is usually the most severe and the only one that causes flu-like symptoms.

HIV/AIDS

Like herpes, HIV/AIDS is caused by a virus that is incurable but treatable. While AIDS can be fatal, many people now live well with HIV for decades with proper treatment.

Sometimes, an early infection doesn’t cause any symptoms. When it does, they’re primarily flu-like plus:

• Rash
• Night sweats
• Mouth ulcers

Early on, HIV is referred to as HIV infection or HIV disease. It may eventually progress to AIDS (acquired immune deficiency syndrome), especially without treatment.

AIDS symptoms include:

• Rapid weight loss
• Regular fevers
• Profuse night sweats
• Extreme fatigue
• Long-term swelling of the lymph nodes
• Long-lasting diarrhea
• Mouth, genital, or anal sores
• Pneumonia
• Discolored skin blotches
• Neurological problems including depression and memory impairment

Thanks to available treatment, most people with HIV infections never develop AIDS.

Syphilis

Syphilis is a bacterial infection that progresses in stages. 

Primary Stage

The primary (first) stage is typically a single, small sore that isn’t painful. It may be on or near the genitals, anus, lips, or mouth. Nearby lymph nodes may swell at this point.

Secondary Stage

If it’s not treated, it may move into the secondary stage. It often begins with a skin rash, usually on the hands and feet. This rash isn’t itchy and can be very faint. It may be accompanied by:

• Flu-like symptoms 
• Patchy hair loss
• Unintended weight loss 

Untreated syphilis may not develop further (although you can still spread it). This is called a latent stage.

Tertiary Stage

In some people, it can advance to the tertiary (third) stage, which is extremely serious. It usually begins between 10 and 30 years after your initial infection.

Tertiary syphilis attacks several organ systems, including the circulatory system (heart and blood vessels) and the nervous system (nerves and brain). The damage it causes can be fatal.

Neurosyphilis

At any time after infection, syphilis can spread to the brain and cause neurosyphilis. Symptoms include:

• Severe headache
• Muscle weakness
• Problems with muscle movement
• Cognitive changes (problems focusing, confusion, personality changes, dementia)

Syphilis is curable with antibiotics. Organ damage may not be reversible, though, so it’s best to get treated early.

When to Get Tested

You should get tested for STIs any time you know or suspect you’ve been exposed or if you develop symptoms consistent with one or more STIs.

CDC recommendations for who should be tested and how often are:

• Everyone between 13 and 64 should be tested for HIV at least once.
• Sexually active females under 25 should be tested every year for gonorrhea and chlamydia.
• Females over 25 with new or multiple sex partners, or with a sex partner who has an STI, should also be tested yearly for gonorrhea and chlamydia.
• Anyone who’s pregnant should be tested early in pregnancy for syphilis, HIV, hepatitis B, and hepatitis C. Those with a high chance of having chlamydia and gonorrhea should also be tested for these infections. 
• Anyone with sexual behaviors that are known to raise incidence levels, or who share drug injection equipment, should be tested annually for HIV.
• If you’ve had oral or anal sex, ask your healthcare provider about throat and rectal testing.

Because of the increased risk of HIV and other STIs among those with male genitalia whose sexual partners also have male genitalia, extra testing is recommended, as follows:

• At least once a year for HIV, syphilis, chlamydia, and gonorrhea
• More frequent testing (every three to six months) for those with multiple or anonymous partners
• If you’re living with HIV, at least once a year for hepatitis C
  

Summary

Some sexually transmitted infections can cause flu-like symptoms such as fever, sore throat, and swollen lymph nodes. These include gonorrhea, hepatitis B, herpes, HIV/AIDS, and syphilis.

Comparing full symptoms lists may help you determine whether you need to be checked for STIs. You should also get tested if you have or may have been exposed to an STI.

The CDC recommends annual or more frequent testing for people at risk of STIs.

A Word From Verywell 

Sexually transmitted infections come with a social stigma. That makes some people reluctant to get tested or to disclose an infection to their sexual partners.

The safest thing to do, though, is to get tested and share your STI status with potential partners before having sex. Getting treatment, wearing condoms, and taking other safer sex precautions can help stop the spread of STIs.