Mycobacterium intracellulare is a bacterium commonly found in natural environments. These bacteria belong to a larger group known as nontuberculous mycobacteria (NTM). While generally harmless to most individuals, Mycobacterium intracellulare can lead to infections, particularly in those with compromised immune systems or pre-existing health conditions.
What is Mycobacterium Intracellulare
Mycobacterium intracellulare is a species within the genus Mycobacterium, which includes Mycobacterium tuberculosis, the bacterium causing tuberculosis. Unlike Mycobacterium tuberculosis, M. intracellulare is classified as a nontuberculous mycobacterium (NTM). These bacteria are characterized as Gram-positive, nonmotile, acid-fast rods that can appear short to long. They form smooth, unpigmented colonies, though older ones may become yellow.
This bacterium is prevalent in the environment, found in soil, fresh and salt water, and household dust. It can adhere to surfaces within plumbing systems, forming biofilms. While widespread, M. intracellulare is an opportunistic pathogen, primarily causing disease in individuals with weakened immune systems or certain underlying health issues. Infection occurs through inhalation or ingestion of the bacteria from these environmental sources.
Health Conditions Associated with Mycobacterium Intracellulare
Mycobacterium intracellulare can cause a range of infections, with pulmonary disease (lung infection) being the most common. Symptoms include chronic cough, fatigue, unintended weight loss, night sweats, or coughing up blood. These symptoms may persist or worsen even if other lung conditions are being treated. Low-grade fevers may also occur.
Beyond lung infections, Mycobacterium intracellulare can also lead to disseminated disease, where the infection spreads throughout the body, affecting multiple organs. This is more common in individuals with severely compromised immune systems, such as those with advanced HIV/AIDS or organ transplant recipients. Lymphadenitis, a swelling of the lymph nodes, is another less common infection, most frequently seen in young children.
Higher risk populations include individuals with pre-existing lung conditions like chronic obstructive pulmonary disease (COPD), bronchiectasis, or cystic fibrosis. Those with weakened immune systems due to conditions like HIV/AIDS, cancer, autoimmune disorders, or immunosuppressive treatments are also more susceptible. Postmenopausal women and individuals over 65 years old also have an increased likelihood of developing Mycobacterium avium complex (MAC) lung disease, which includes M. intracellulare infections. Mycobacterium intracellulare infections are generally not transmitted from person to person.
Identifying and Managing Infections
Diagnosing Mycobacterium intracellulare infections involves a combination of clinical evaluation, imaging studies, and laboratory tests. Doctors look for symptoms compatible with NTM pulmonary disease and signs on imaging. Radiological criteria include chest X-rays showing nodular or cavitary opacities, or a computed tomography (CT) scan revealing multifocal bronchiectasis with multiple small nodules. These imaging findings help visualize the extent of lung involvement.
To confirm the presence of the bacteria, laboratory tests are performed, such as sputum cultures or bronchoalveolar lavage (BAL). Sputum cultures involve growing bacteria from mucus samples, while BAL collects fluid directly from the lungs. A diagnosis requires at least two positive sputum culture results for the same NTM species or subspecies. The slow-growing nature of M. intracellulare and its widespread environmental presence can make diagnosis challenging, as colonies may take seven or more days to grow on laboratory media.
Treatment for Mycobacterium intracellulare infections involves a multi-drug regimen of antibiotics. A common approach includes a macrolide (such as azithromycin or clarithromycin), along with ethambutol and rifampin. The duration of treatment is prolonged, lasting at least 12 months after sputum cultures consistently test negative for the bacteria. Adherence to this long course of medication is important for successful outcomes.
Patients are monitored for potential side effects, including visual disturbances from ethambutol or hearing loss from macrolides. Routine blood tests check for liver toxicity. Regular follow-up with respiratory specimens and chest CT scans helps monitor the effectiveness of treatment.
Reducing Your Risk of Exposure
Reducing exposure to Mycobacterium intracellulare involves minimizing contact with aerosolized water sources where these bacteria thrive. For individuals, especially those at higher risk, avoiding prolonged exposure to hot tubs, saunas, and steam rooms is advisable. These environments can aerosolize water droplets containing bacteria, which can then be inhaled. Taking baths instead of showers or using a shower head that produces less mist is also suggested, as water spurting from showerheads can distribute pathogen-filled droplets.
Maintaining good indoor air quality and proper hygiene practices can also help. Ensuring adequate ventilation in bathrooms by opening windows or using a fan can reduce the concentration of aerosolized mycobacteria during showering. Cleaning showerheads regularly by disassembling and scrubbing them with soapy water or vinegar can help remove biofilms where these bacteria grow. Keeping potting soil moist and wearing a mask, such as an N-95, when handling it can also reduce the inhalation of soil particles containing NTM. While complete avoidance is difficult due to the widespread presence of M. intracellulare in the environment, these measures can help reduce the risk of exposure, particularly for vulnerable individuals.