What is Mycobacterium avium Complex?

The Mycobacterium avium complex comprises of several types of nontuberculous mycobacteria (NTM), similar organisms that cannot be told apart in a typical lab and need genetic testing to be identified. M. avium and Mycobacterium intracellular are two original members of this complex, known for about a century. In 2004, Mycobacterium chimaera was added to this complex. Some also consider Mycobacterium subspecies paratuberculosis part of this complex. The most recent addition is the Mycobacterium paraintracellulare, discovered in lung diseases in Southeast Asia in 2016.

M. avium was first noticed in chickens in 1933 when it caused a cavity-like disease that had a resemblance to tuberculosis. It’s only years later that cases in humans were noticed. The Mycobacterium avium complex is the major cause of infections in humans by nontuberculous mycobacteria species, particularly affecting the respiratory system.

What Causes Mycobacterium avium Complex?

The M. avium complex is a type of typically stationary bacteria that doesn’t form spores. It grows slowly, needing roughly 10 to 20 days to form mature colonies. This complex is part of the Runyon classification’s class III group of bacteria. One noteworthy characteristic is that this bacterium prefers specific temperatures to grow: M. avium prefers 34.5 C and Mycobacterium intracellulare prefers 31.5 C. However, they can still grow between 28 C to 38.5 C. Interestingly, most M. avium bacteria can survive at 49 C, while only 10% of M. intracellulare can handle this temperature.

Another bacterium, Mycobacterium scrofulaceum, has a lot of similarities with the M. avium complex in terms of biochemical properties; they belong to the same group. The M. avium complex is divided into four main subspecies or strains. M. avium subspecies Avium tend to cause lung infections, while the M. avium subtype hominissuis mainly impacts the digestive system.

An intriguing aspect is the potential link of the M. avium subspecies paratuberculosis to a specific disease in animals and possibly humans. In animals like cows, this bacteria can cause Johne’s disease. Some researchers suspect a link between this bacteria and Crohn’s disease in humans, but strong evidence has yet to materialize. The presence of antibodies against this bacteria was found to be significant in patients with inflammatory bowel diseases.

In 2004, a new form of the M. avium complex was discovered named Mycobacterium chimaera. This bacterium becomes relevant in cases of contamination during surgical procedures, where it can cause device-related infections.

The M. avium complex can be identified by biochemical reactions, but these methods are not refined enough for use in clinical settings. More advanced techniques like polymerase chain reaction (PCR) have been developed. These methods allow us to identify the individual components of the M. avium complex. Other methods like Restriction Fragment Length Polymorphism (RFLP) and Multilocus Sequence Typing (MLST) also help in identifying and diagnosing M. avium complex infections.

Risk Factors and Frequency for Mycobacterium avium Complex

Mycobacterium avium complex is a bacteria that is found all around the world, including in the Americas, Asia, and Europe. It is present in various sections of society, with some areas experiencing more cases than others. In the United States, for example, the number of cases can range from 1.4 to 6.6 out of every 100,000 people. Although there is no specific area where the disease is especially common, the number of infections has been increasing lately.

We’ve also noticed that mycobacterium avium complex infections follow a pattern throughout the year. More cases are usually reported in late winter and spring, with fewer in the fall. Women tend to have a higher chance of getting infected compared to men, but an Australian study found the opposite, suggesting that men were more at risk.

It’s worth noting that the kind of lung-related problems women face with infection could be a factor in these differences. Women are more likely to develop a specific type of disease related to this bacteria, known as Lady Windermere syndrome.

Mycobacterium avium complex is found globally.
The bacteria is more common in certain areas, with the number of infections increasing recently.
More infections are reported in late winter and spring.
Women generally have a higher chance of getting the disease, but some studies show men might be more vulnerable.
Women are more prone to develop a particular lung condition known as Lady Windermere syndrome.

This bacteria can also be found in various places in our environment like soil, air, bathrooms, house dust, birds, farm animals, hot water systems, and even cigarette components. Scientists are yet to determine its specific ecological niche, that is, the conditions under which it thrives best.

Signs and Symptoms of Mycobacterium avium Complex

Mycobacterium avium complex includes several types of infections such as lung disease, infections of the skin and soft tissues, musculoskeletal infections, scattered disease throughout the body, infections related to catheters, and swollen lymph nodes. The most commonly seen form is lung disease. These infections can occur in people with both healthy immune systems and those with weakened immune systems, including patients with HIV. As new types of Mycobacterium avium complex continue to be identified, it’s still unclear how widespread each type is.

There are several risk factors for developing Mycobacterium avium complex lung disease. These include having specific lung conditions such as pneumoconiosis, chronic obstructive pulmonary disease (COPD), cystic fibrosis, or other chronic lung diseases. People with certain physical abnormalities like severe scoliosis or straight back syndrome, as well as those with a particular type of heart valve issue (mitral valve prolapse), are also at risk. People with significantly low CD4 counts – an issue common in certain cancers and in AIDS patients – are more likely to suffer from these infections. Other risk factors include being an elderly woman who suppresses coughs, having a suppressed immune system after organ transplant, and having problems with interferon-gamma production or reception. Siblings of the infected patient are at higher risk compared to the general population. There are no known risk factors for skin infections or swollen lymph nodes caused by Mycobacterium avium complex.

Mycobacterium avium complex lung disease can take different forms as seen in X-rays and CT scans. Common symptoms in patients with healthy immune systems span from nonspecific symptoms like a chronic cough to rarer occurrences like fever and coughing up blood. Both white men and elderly Caucasian women are susceptible to different forms of the illness, manifested through worsening cough, coughing up of blood, and systemic symptoms.

X-rays may not show all the details of the lung disease, thus a high-resolution CT (HRCT) scan is often more effective in revealing changes such as small nodules, bronchiectasis (widespread and often permanent enlargement of parts of the airways of the lung), and pleural thickening (thickening of the lining of the lungs).

Mycobacterium avium complex can also lead to cervical lymphadenitis (swollen lymph nodes in the neck), usually seen among children. Additionally, in some cases, it can cause something similar to hypersensitivity pneumonitis, which was initially believed to be solely an allergic reaction, but now is considered to be a combination of infection and inflammation. People with AIDS or those with suppressed immune systems are particularly susceptible to widespread infections.

Testing for Mycobacterium avium Complex

Being infected with Mycobacterium avium complex, a type of bacteria, can sometimes show no symptoms. There’s ongoing debate as to whether these bacteria can settle in the respiratory tract without causing infection when it comes to non-tuberculosis mycobacterial diseases. Because bacteria from other sources might contaminate a sputum sample (a mixture of saliva and mucus coughed up), more than one sample is necessary for accurate testing.

The symptoms of this infection are quite vague and could point to many different diseases, so the only surefire way to diagnose it is through isolating the bacteria in a lab test. According to guidelines set by the Infectious Disease Society of America, if a doctor suspects a patient has a non-tuberculous mycobacterial infection, they should carry out a thorough evaluation, which includes radiology tests (like X-rays), microbiology tests (lab tests to identify bacteria or other microorganisms), and a clinical evaluation (a detailed examination of the patient’s overall health condition). It’s also really important at this stage to rule out pulmonary tuberculosis, another lung infection which often presents similar symptoms.

The doctors should also assess for any pre-existing conditions that might increase a patient’s risk of developing mycobacterial diseases, and they should also ensure that the patient would be able to handle prolonged treatment with multiple drugs, as the treatment can be long and carries the risk of side effects.

While Mycobacterium avium complex doesn’t naturally live in the lungs, not all patients who test positive for it in their sputum need to be treated. The decision to proceed with treatment is made after considering several factors- lab test results, radiology test results, and the patient’s overall health condition. The aim is to avoid unnecessary long-term treatment that could potentially cause adverse drug reactions.

Treatment Options for Mycobacterium avium Complex

Mycobacterium avium complex (MAC) infections, a type of lung infection caused by specific bacteria, are typically treated with a type of antibiotic called macrolide. The Infectious Disease Society of America recommends using three different antibiotics to treat severe MAC infections. For less serious cases, two antibiotics may be enough.

While some patients may be observed without immediate treatment, MAC lung infections tend to get worse over time, meaning treatment is usually necessary eventually. To monitor the disease, doctors generally recommend checking mucus samples every three months, and using imaging techniques like x-rays or HRCT scans every six months. These methods help doctors see the impact of the disease on the lungs. People who have cavities in their lungs, are underweight, older, or have other health problems are more likely to see their condition worsen.

Various medications, including macrolides and other antibiotics, are used to treat MAC infections, but there isn’t necessarily a direct relationship between a drug’s effectiveness in a lab and its effectiveness in a person’s body. The primary goal of treatment is for lab tests to show no signs of the disease for 12 months, which usually takes three to six months of treatment to achieve. Regular health checks during treatment are important to monitor any side effects of the medication.

In severe cases, a treatment plan might involve daily oral antibiotics, and possibly an injected drug during the initial phase of treatment. More severe localized cases might even need surgery after the disease is no longer detectable in sputum tests. For less serious cases, intermittent doses of the three-drug treatment may be enough.

It’s important to note that no studies have directly evaluated the success of these treatment methods, but long-term effectiveness rates are quite high. Close monitoring for worsening symptoms and medication side effects is crucial to successful treatment. When starting a new medication, it’s often best to start with a low dose and gradually increase it. Sometimes, doctors may need to check the medication levels in the blood, especially if the disease is not responding to treatment or if there is a concern about the body’s ability to absorb the medication.

Overall, treating MAC infections involves careful monitoring and multiple drugs, and may take quite some time before the disease is no longer detectable. Treatment must be personalized based on the patient’s disease severity and their individual health. Your healthcare provider will work closely with you to find the best treatment plan.

These are some health conditions that could show similar symptoms and hence, might be taken into account by doctors during the diagnosis process: