What Is a Bacterial Infection?

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Bacterial infections are caused by small, single-cell organisms called bacteria that invade the body. These infections are common, and there are many ways you can get them.

An overgrowth of harmful bacteria causes a bacterial infection. Different types of bacteria can cause different symptoms. Healthcare providers may prescribe various antibiotics depending on the type of bacterial infections.

This article discusses what you need to know about bacterial infections. It explains the symptoms, causes, and types of bacterial infections. Diagnostic tests and treatment options are also covered.

Bacterial Infection Symptoms

Verywell / Laura Porter

Bacterial Infection Symptoms

Bacterial infections can cause generalized symptoms that impact the whole body. These include:

Children and adults of any age can develop a bacterial infection. Bacteria can infect every area of the body, like the bladder, brain, intestines, lungs, and skin.

A bacterial infection can also spread throughout the blood, triggering a potentially life-threatening blood infection called septicemia. That, in turn, can lead to sepsis, a condition that happens when your body has a severe response to an infection.

Localized Symptoms

You can also experience localized symptoms of a bacterial infection, which affect the specific area of the body that is infected. Localized symptoms of a bacterial infection may include:

  • Pain: This is common with bacterial infections. You can experience skin pain with a bacterial infection on the skin. A lung infection can cause pain when breathing, and you can feel abdominal (stomach) pain with an intestinal (or bowel) infection.
  • Skin Rash: Bacterial skin infections, such as impetigo, erythrasma, folliculitis, and methicillin-resistant Staphylococcus aureus (MRSA), can cause a red, itchy, and painful skin rash.
  • Swelling and redness: You may notice redness or swelling on parts of the body that you can see, such as the skin, throat, or ears.
  • Problems with organ function: Internal organs can become inflamed and swollen. While you can't see it, you may feel pain or other effects in these areas. For example, pyelonephritis (a kidney infection) could worsen kidney function.

Additional examples of localized symptoms of bacterial infections:


All bacterial infections have an incubation period, and symptoms can rapidly worsen or progress slowly.

Common Bacterial Infections

The severity of bacterial infections can vary widely and depends on the type of bacteria involved. Bacterial organisms tend to target specific areas of the body. For example, syphilis, a sexually transmitted bacterial infection, is unlikely to affect the stomach or lungs.

On one hand, there are relatively minor illnesses like strep throat and ear infections. But bacterial infections can also cause potentially life-threatening conditions like meningitis and encephalitis. Here is a look at common types of bacterial infections.

Food Poisoning

Food poisoning occurs from eating food that has been infected with bacteria. Common types of bacterial food poisoning include:

  • Salmonella is an infection often linked to food poisoning. It is caused by nontyphoidal salmonellae bacteria, which live in the gastrointestinal tracts (GI) of humans and other animals. Symptoms include severe stomach upset, diarrhea, and vomiting.
  • Escherichia coli (E. coli) also causes GI distress. The infection usually improves on its own, but it can be severe or even fatal. Contaminated food—including uncooked vegetables—can spread E. coli bacteria.

Bacterial Respiratory Infections

When bacteria enter the lungs, it can cause difficulty breathing. Common bacterial lung infections include:

  • Bacterial pneumonia is a lung infection that can be caused by different kinds of bacteria, like Streptococcus pneumoniae, Klebsiella pneumoniae, or Pseudomonas aeruginosa. The bacterial infections spread through air particles from coughing or sneezing.
  • Tuberculosis is a highly contagious disease caused by the Mycobacterium tuberculosis bacteria. It usually leads to a lung infection.

Bacterial Skin Infections

Bacteria on the skin can cause pain, itching, redness, and a rash. Common bacterial skin infections include:

Gastrointestinal Bacterial Infections

Bacterial infections in the digestive tract can cause gastroesophageal reflux disease (GERD), pain, vomiting, and diarrhea. Common bacterial infections that affect the GI tract include:

Genital Bacterial Infections

Bacterial infections that affect the genitals can be caused by an imbalance of good and bad bacteria or transmitted through sexual contact. Common bacterial genital infections include:

  • Bacterial vaginosis is an infection of the vagina that causes itchiness, discharge, and painful urination. While it can be caused by sex, it is not considered a sexually transmitted infection (STI). It happens because of an imbalance in the normal bacterial flora of the vagina.
  • Chlamydia is an STI caused by the bacterium Chlamydia trachomatis.
  • Gonorrhea is an STI caused by the bacteria Neisseria gonorrhoeae.
  • Syphilis is an STI caused by the bacterium Treponema pallidum.

How Bacterial Infections Spread

Bacterial infections are caused by the transmission, or spread, of bacteria. You can become exposed to bacteria from contact with an infected person, touching surfaces with bacteria on it, contaminated food or water, and sex.

Common transmission modes of bacterial infections include:

  • Airborne: Bacterial diseases like tuberculosis are spread through microscopic airborne respiratory droplets. These droplets are expelled when an infected person sneezes, coughs, laughs, or exhales. The bacteria can linger in the air, travel along air currents, or land on surfaces. Another person can contract the illness when the bacteria enters their body by inhalation or contact with mucus membranes.
  • Contaminated food or water: Bacteria can be spread by ingesting undercooked food or contaminated water. Bacteria that cause food-borne illnesses include Clostridium botulinum, Campylobacter, Salmonella, and E. coli. 
  • Contaminated objects: Bacteria can cling to surfaces and be transmitted through contact with contaminated objects and surfaces.
  • Insect bites: Bacterial infections can be spread through insect bites. Ticks can carry bacteria from the Borrelia family, which causes Lyme disease, or Rickettsia bacteria, which causes typhus and spotted fever. Lice can transmit bacteria, including bartonellosis (Trench fever), borreliosis (relapsing fever), and rickettsiosis (typhus). 
  • Sex: Sexually transmitted bacterial infections include chlamydia, gonorrhea, and syphilis.

Anyone can get sick when exposed to bacteria. But, having a weakened immune system puts you at a higher risk of severe bacterial infections. Certain conditions and medications can suppress your immune system, making it weaker. Even bacteria that normally belong in your body can put you at risk.


To diagnose a bacterial infection, your healthcare provider may:

  • Take a sample of fluids such as pus or mucus, which can help identify an STI, and send it to a laboratory
  • Send in a swab sample from your throat, ear, or infected area of your skin for evaluation
  • Evaluate a urine sample, which can identify bladder and kidney bacterial infections
  • Evaluate a stool sample to help determine the bacterial cause of persistent GI upset

The pattern of your symptoms can help your healthcare provider diagnose your bacterial infection. The location, timing, and severity of your symptoms can point to a bacterial infection.

Blood Tests

Blood tests can help identify a bacterial infection. With a bacterial infection, people tend to have increased white blood cells (WBCs), which work together to defend the body from infections. A blood test called a complete blood count (CBC) can detect elevated WBCs.

Your healthcare provider may also order what's known as a CBC with differential. This test tells whether specific types of WBCs have increased in your blood.

Imaging Studies

Infectious bacteria can cause a bacterial abscess (an enclosed, pus-filled area). If your healthcare provider thinks you might have an abscess in or near internal organs, you may need an imaging study to help identify it.

An X-ray, for example, can help diagnose pneumonia.

How to Treat a Bacterial Infection

Bacterial infections can last for days to weeks but often go away on their own without antibiotics. That said, you may need prescription antibiotics if your body is unable to fight off a bacterial infection.

If you have symptoms like fever, pain, swelling, coughing, or dehydration, your healthcare provider may suggest anti-inflammatory medication.

Untreated bacterial infections can spread or linger, causing major health problems. Although it's rare, untreated bacterial infections can even be life-threatening.

Other organisms, like viruses, parasites, and worms, can also cause infections. Treatment depends on the infectious microorganism.


The type of bacteria you have will help determine which antibiotics you need to take. Most antibiotics work against more than one type of bacteria, but not against them all.

There are different ways that you can take antibiotics. You can take them:

  • By mouth
  • Topically or on the surface of the skin or eye
  • Through intravenous therapy (IV)

If you're using a prescription antibiotic, make sure you use it as directed. For example, don't use a skin antibiotic on your eyes. It's important to take your medication exactly as prescribed and for the complete duration of your prescription.

Supportive Care

Your healthcare provider might prescribe pain medicine or anti-inflammatory medication. These medications can help ease the pain and swelling from your bacterial infection.

If you have a fever, your doctor may also recommend fever-reducing medication. Non-steroidal anti-inflammatories (NSAIDs) can reduce fevers, swelling, and pain.

If you have a painful cough, your doctor may suggest anti-cough medication. You may need IV fluids if you're becoming dehydrated.


If you have an abscess, you may need to have surgery to treat it. This can be a simple procedure for a superficial abscess in the skin. But, an abscess located deep in the body—like in the brain or intestines—may require more extensive surgery to remove it.

How to Prevent Bacterial Infections

Bacterial infections can often be prevented. To prevent bacterial infections:


Bacterial infections are incredibly common and are also quite different from one to another. The type of bacteria involved, its cause, location, and timing all influence the course of your infection.

Even symptoms vary a great deal. Some infections can worsen and cause severe complications. Diagnosis and treatment options depend on the specific bacterial infection you may have.

You're likely going to have at least a few bacterial infections throughout your life. Using an antibiotic "just in case" you have a bacterial infection is never a good idea. Reusing an old prescription is also not recommended. Your infection could get worse from taking the wrong medicine, and you could develop bacterial resistance if you use antibiotics unnecessarily.

If you think you have a bacterial infection that needs treatment, talk to your healthcare provider.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Kristina Duda, RN
Kristina Duda, BSN, RN, CPN, has been working in healthcare since 2002. She specializes in pediatrics and disease and infection prevention.