Anaerobic Infections

Written by Amber Erickson Gabbey
Medically Reviewed by George Krucik, MD, MBA on June 18, 2013

What are Anaerobic Infections?

Anaerobic infections are common infections caused by anaerobic bacteria. These bacteria are naturally occurring and plentiful in and on the body. They are the most common flora in the body. They don’t cause infection in their natural state, but can cause infection after injury or trauma to the body. Anaerobic infections commonly affect the abdomen, genitals, heart, bone, joints, central nervous system (CNS), respiratory tract, skin, and mouth.

Anaerobic infections are a cause for concern because they are often difficult to treat. Common anaerobic infections include:

  • appendicitis
  • abscess (brain, abdominal, lung, peritonsillar, liver, and tubovarian)
  • sinusitis
  • tetanus
  • pneumonia
  • Lemierre’s syndrome
  • periodontitis
  • peritonitis

What Causes Anaerobic Infections?

Anaerobic infections are often caused when deep tissues inside the body become injured and/or exposed. This can be by injury, trauma, or surgery. Specific causes can include surgery, bites, and root canals.

People with low blood supply, weak immune systems, and diabetes are at the highest risk.

Symptoms of Anaerobic Infections

The most common indicators of anaerobic infection include:

  • noticeable infection near the skin
  • smelly discharge
  • pus-filled abscess
  • tissue damage or gangrene
  • discoloration of infected area

Other symptoms can occur at the location of the infection. For example, infection in the mouth or throat could cause tender gums, bad breath, or pain. Infection in the lungs may cause chest pain or coughing. Infection of the skin could cause pain, redness, or swelling.

Diagnosing Anaerobic Infections

To diagnose anaerobic infection, first a physical examination is performed. A doctor then asks about symptoms. Testing of infected tissue can identify the bacteria responsible for the infection. For internal infections, an X-ray or imaging scan may be needed.

Treating Anaerobic Infections

Anaerobic infections are usually treated with antibiotics and other medications, along with drainage. Drainage is necessary to successfully treat the infection. In some cases, the infection or abscess will need to be surgically removed.

Anaerobic Infection Prognosis

Anaerobic infections are serious and can be life-threatening if not treated properly and quickly.  Most people make a complete recovery following proper treatment for the infection.

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Show Sources

  • Hedberg, M. & Nord, C. E. (n.d.). Anaerobic Bacteria. Retrieved June 6, 2013, from
  • Jenkins, S. (2001). Infections due to anaerobic bacteria and the role of antimicrobial susceptibility testing of anaerobes. Reviews in Medical Microbiology, 12(1), 1-12. Retrieved June 6, 2013, from
  • Lofmark, S., Edlund, C. & Nord, C. E. (2010). Metronidazole is still the drug of choice for treatment of anaerobic infections. Clinical Infectious Diseases, 50 (supplement 1), S16-S23. Doi: 10.1086/647939
  •  TestID: MMLSA Antimicrobial Susceptibility, Anaerobic Bacteria, MIC (n.d.).. Mayo Clinic. Retrieved June 6, 2013, from

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