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Atypical Mycobacterial Infections

Last updated Feb. 23, 2018

Approved by: Maulik P. Purohit MD MPH

Atypical Mycobacterial Infection is any infection caused by a species of mycobacteria that does not result in classical tuberculosis.


What are the other Names for this Condition? (Also known as/Synonyms)

  • Non-Tuberculous Mycobacterial Infection

What is Atypical Mycobacterial Infection? (Definition/Background Information)

  • Atypical Mycobacterial Infection is any infection caused by a species of mycobacteria that does not result in classical tuberculosis
  • The species of mycobacterium that can cause Atypical Mycobacterial Infection include:
    • Mycobacterium avium-intracellulare
    • Mycobacterium kansasii
    • Mycobacterium marinum
    • Mycobacterium ulcerans
    • Mycobacterium chelonae
    • Mycobacterium fortuitum
    • Mycobacterium abscessus
  • Any individual may develop Atypical Mycobacterial Infections; although, the elderly and those with certain pre-existing conditions and compromised immune systems, are at the highest risk for developing the same
  • Infection by Mycobacterium spp. (which do not cause tuberculosis) can be initiated when an individual comes into contact with the pathogen either through inhalation, or via cuts, abrasions, and wounds on skin
  • Signs and symptoms of Atypical Mycobacterial Infections vary, depending on the type of species causing the infection. These may include cough, shortness of breath, skin lesions, and swollen lymph nodes
  • The diagnosis is made through culture of body fluids and tissues, including of blood, sputum, and skin. Imaging methods, such as chest X-rays and CT scans, are also used, if a lung infection is suspected
  • Prescription antibiotics are typically the mainstay of treatment for Atypical Mycobacterial Infections. The prognosis is good for a majority of the affected individuals, with prompt diagnosis and appropriate treatment

Who gets Atypical Mycobacterial Infection? (Age and Sex Distribution)

  • Individuals of all ages can develop Atypical Mycobacterial Infections. However, elderly adults and individuals with poor/weak immunity, are more likely to develop such infections
  • Males and females are equally susceptible to developing the infection. But, the specific susceptibility of each gender may also depend on the mycobacterial species type causing the infection
  • No racial or ethnic predilection is reported in the occurrence of this infection that is observed worldwide

What are the Risk Factors for Atypical Mycobacterial Infection? (Predisposing Factors)

The risk factors for Atypical Mycobacterial Infection include:

  • Older adults
  • Having an underlying lung condition, such as COPD, or a lung injury from a previous episode of tuberculosis, or other lung conditions
  • Having tall and slender physical features, including a curved spine, abnormalities of the breastbone, and mitral valve prolapse. Females with these characteristics are especially at risk for infection
  • A weakened immune system from certain illnesses or drugs
  • Having esophageal disorders, which may result in spillage of the gastric contents into the lung leading to lung infections
  • Exposure to environments where atypical mycobacteria are found. These include soil, hot tubs and pools
  • Having untreated open wounds
  • Smoking and alcohol abuse

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Atypical Mycobacterial Infection? (Etiology)

Atypical Mycobacterial Infections are caused by any species of non-tuberculous mycobacteria. Up to 13 distinct species of atypical mycobacteria are known to cause human infection.

  • The most common species of mycobacterium that cause such infections include:
    • Mycobacterium avium-intracellulare
    • Mycobacterium kansasii
    • Mycobacterium marinum
    • Mycobacterium ulcerans
    • Mycobacterium chelonae
    • Mycobacterium fortuitum
    • Mycobacterium abscessus 
  • The bacteria gain entry into the body in the following manner:
    • Through inhalation from the environment
    • Via untreated cuts and abrasions, when swimming, wading through contaminated pools, or any action that causes a part of the body to be submerged in contaminated water
    • Injection with needles containing nontuberculous mycobacteria
    • Surgical procedures with contaminated instruments
    • Untreated open wounds, which allow mycobacteria to enter the body upon exposure

There is little evidence of person-to-person spread of atypical mycobacterial organisms. The exception to this is organisms that cause skin lesions, as well as M. kansasii and M. simiae.

What are the Signs and Symptoms of Atypical Mycobacterial Infection?

The signs and symptoms of Atypical Mycobacterial Infections vary depending on the species of nontuberculous mycobacteria infecting the individual. The symptoms may also vary from one individual to another.

Some mycobacterial species and the symptoms they cause include:

  • Mycobacterium avium-intracellulare causing:
    • Fever and fatigue
    • Swollen lymph nodes
    • Diarrhea
    • Weight loss
    • Shortness of breath
  • Mycobacterium kansasii causing:
    • Fever
    • Swollen lymph nodes
    • Lung crackles due to fluid accumulation in lungs
    • Wheezing
    • Skin lesions that are either seen in isolation, or as part of a more widespread disease
  • Mycobacterium marinum causing:
    • A single lump or pustule (pus-filled bump) that breaks down and forms a crusty sore or abscess, usually on the elbows, knees, feet, knuckles, or fingers
    • Other lumps that form around the initial lesion
    • Multiple skin lesions in individuals with a compromised immune system
    • Red, swollen, and tender joints, observed in rare occasions
  • Mycobacterium ulcerans causing:
    • Nodules to develop within 2 weeks of infection, through broken skin
    • Painless, individual nodules (or growth of abnormal tissue) that are 1-2 centimeters large and can be itchy
    • The nodule may rupture after a few months and form an ulcer, which rapidly spreads to up to 15% of the skin surface
  • Mycobacterium chelonae causing:
    • Lung disease
    • Joint infections
    • Eye disease
    • A non-healing wound, or nodule beneath the skin, or an abscess
    • Widespread lesions in individuals with a compromised immune system
  • Mycobacterium abscessus causing:
    • Skin infections from a puncture wound
    • Lung infection and widespread infection in individuals with a compromised immune system
  • Mycobacterium fortuitum causing:
    • Local skin infections
    • Osteomyelitis (inflammation of bone)
    • Joint infections
    • Eye disease
    • Widespread skin and soft tissue lesions in severely immunocompromised individuals, such as AIDS patients
    • Non-healing ulcerative skin lesions, or nodules under the skin
  • Atypical Mycobacterial Infections in children are most frequently located in the upper neck region or below the chin. Most children affected are typically healthy (i.e., not immunocompromised).

How is Atypical Mycobacterial Infection Diagnosed?

The diagnosis of Atypical Mycobacteria Infections is made through the following tools:

  • A complete physical examination and review of medical history
  • Assessment of the presenting symptoms
  • Imaging methods, including radiographic imaging studies, CT scans, and chest X-rays
  • A culture of tissue, blood, or sputum (mucus-like fluid in the respiratory tract): Tissues, blood, or sputum are sent to the lab and cultured under specific conditions, to determine the species of mycobacteria causing the infection
  • Skin biopsy (or tissue biopsy) of the affected area: A skin/tissue biopsy is performed and sent to a laboratory for a pathological examination. The pathologist examines the biopsy under a microscope. After putting together clinical findings, special studies on tissues (if needed) and with microscope findings, the pathologist arrives at a definitive diagnosis
  • Polymerase chain reaction (PCR) testing of swabs of ulcers or tissue biopsies, to identify the specific mycobacterium

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Atypical Mycobacterial Infection?

  • The complications of Atypical Mycobacterial Infections depend on the type of nontuberculous mycobacterial species causing the symptoms
  • Elderly adults or immunocompromised individuals (particularly those diagnosed with HIV infection or AIDS) are the most likely candidates to develop complications, which may be severe

How is Atypical Mycobacterial Infection Treated?

The treatment measures for Atypical Mycobacterial Infections depend on the species of non-tuberculous mycobacteria causing the infection. The treatment options may include:

  • Treatment with antibiotic medications:
    • More than one type of antibiotic is typically prescribed (usually 2 or 3), due to the relative antibiotic-resistant nature of nontuberculous mycobacterial pathogens
    • The treatment with antibiotic medications may continue for a year or more, until the lab culture results are negative
  • Surgical drainage of skin lesions
  • Curettage (scraping or scooping) of skin lesions
  • Surgery to remove skin lesions, infected lymph nodes, or infected lung tissue

How can Atypical Mycobacterial Infection be Prevented?

Specific prevention options for Atypical Mycobacterial Infections depend on the infecting species type. Some general methods to help prevent Atypical Mycobacterial Infections include: 

  • Avoiding exposure to contaminated water, especially in pools or spas
  • Treating open wounds and cuts
  • Making sure to use disinfected needles or surgical tools
  • Washing/cleaning surgical tools with uncontaminated sources
  • Seeking proper treatment for pre-existing diseases and conditions that may result in a compromised immune system

What is the Prognosis of Atypical Mycobacterial Infection? (Outcomes/Resolutions)

The prognoses of Atypical Mycobacterial Infections are generally positive with proper treatment. Nevertheless, the possible outcomes of an Atypical Mycobacterial Infection include:

  • With treatment, these infections can be cured successfully
  • Without treatment, Atypical Mycobacterial Infections can result in complications and further disease, depending on the type of nontuberculous mycobacteria infecting the body
  • The elderly and immunocompromised individuals, such as those with HIV infection and AIDS, are especially vulnerable to such complications 

Additional and Relevant Useful Information for Atypical Mycobacterial Infection:

  • The most common manifestation of Atypical Mycobacterial Infections is lung disease, showing in 94% of cases
  • Lymphatic disease presents in roughly 3% of the cases, while skin, soft tissue, and disseminated disease makes up the other 3%
  • The most common Atypical Mycobacterial Infection associated with AIDS involves M. avium-intracellulare, also known as mycobacterium avium complex (MAC)

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Helpful Peer-Reviewed Medical Articles:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: July 17, 2017
Last updated: Feb. 23, 2018