What is Atypical Mycobacterial Disease?
Atypical mycobacteria, also known as nontuberculous mycobacteria, are organisms that can cause various diseases. These diseases include skin and soft tissue infection, lymph node inflammation, lung infection, widespread infection throughout the body, and several other less common infections. The most common types of these bacteria that cause most human infections are the MAC bacteria (Mycobacterium avium complex), Mycobacterium avium, Mycobacterium intracellulare (also known as MAI), Mycobacterium kansasii, Mycobacterium marinum, Mycobacterium ulcerans, Mycobacterium abscessus complex bacteria, Mycobacterium chelonae, and Mycobacterium fortuitum.
These bacteria are usually found in soil, water sources both indoor and outdoor, and can even be found on poorly cleaned medical equipment. Atypical mycobacteria most commonly infect young children, people with weakened immune systems, people who have medical equipment installed in their bodies, and those who’ve recently had surgeries or similar procedures.
These bacteria can be sorted into two types: those that grow slowly and those that grow quickly. They are also grouped by the body systems they typically affect. Identifying atypical mycobacteria can be difficult due to their shape and growth patterns, so tests can be challenging. Treating these infections often includes lengthy periods using a combination of antibiotics and often requires surgery.
What Causes Atypical Mycobacterial Disease?
Atypical mycobacteria, a type of bacteria, have a standout quality: they are acid-fast bacilli. This means they get a certain color when a specific staining method called the Kinyoun method is used. The reason they turn this color is due to their outer layer made of a substance known as mycolic acid. This outer layer helps them create strong clusters called biofilms, which allow them to survive in harsh conditions.
These biofilms have a couple of benefits for the bacteria. They make it harder for antibiotics to penetrate and kill the bacteria. They also allow the bacteria to survive in different temperatures and protect them from getting killed by substances like chlorine, disinfectants, and cleaning products that are used to purify water. The bacteria can also survive in environments with a lot of oxygen or no oxygen due to the formation of these biofilms.
These bacteria are also slow growers. Atypical mycobacteria are divided into two categories: rapid and slow-growing. The rapid-growing ones take 7 to 30 days to grow in a lab dish. The slow-growing ones will take several weeks to months to show growth.
The kind of disease caused by these bacteria will depend on how they enter the body and how likely the person is to get the infection. The bacteria can cause a lung infection if you inhale material containing the bacteria. Swollen lymph nodes can be a result of ingesting the bacteria or if they penetrate through soft tissues. Infections of the skin and soft tissue can occur if the bacteria get in through broken skin or via implanted medical devices.
Risk Factors and Frequency for Atypical Mycobacterial Disease
Atypical mycobacteria are found in both natural and man-made environments. They are most commonly found in soil and water, with higher concentrations in pine forests and swampy areas of the southern United States. Urban areas and man-made water sources, like plumbing systems, showers, and hot tubs, also host these bacteria because they can resist common water treatment chemicals.
Each year, between 5 to 10 out of every 100,000 people develop a lung disease caused by these bacteria. The rate of all atypical mycobacterial infections in children is estimated to be between 0.6 to 3.3 per 100,000. For adults, the estimated rate of infection is between 20 to 47 per 100,000 people.
- Atypical mycobacterial lung disease primarily affects adults and those with weakened lung defense systems. This includes people with conditions like HIV, people taking certain medications, and those with cystic fibrosis.
- The disease is more often seen in white, middle-aged or older men who have other conditions like chronic obstructive pulmonary disease, alcohol use, or tobacco use.
- A rare form of the disease, often called “hot tub lung,” occurs as a response to exposure from bathing or recreational water activities.
- Disseminated atypical mycobacterial disease (MAC/MAI) is mostly seen in individuals with severely weakened immune systems, such as people with AIDS.
Signs and Symptoms of Atypical Mycobacterial Disease
Lymphadenitis, a condition causing inflammation in the lymph nodes, is more frequently seen in children under five. Parents might notice soft yet firm lumps under their child’s skin, typically located in the regions under the jaw or in the neck area. Initially, these lumps are painless but over time, they can become more pliable and sometimes even lead to a pus-like discharge. A common indicator that a child might have lymphadenitis is when an enlarged node in the neck doesn’t respond to usual antibiotics or doesn’t diminish even when monitored closely.
Mycobacterial infections can also manifest in skin and soft tissue. These infections can affect patients of any age and occur due to a localized or a wide-spread infection. Risk factors include recent trauma to the skin when swimming in different kinds of water bodies, immune-suppression or recent surgeries. The skin lesions come in various forms, ranging from red bumps that eventually turn into ulcers, to skin eruptions that resemble cellulitis. A distinct type of skin lesion called Buruli ulcer starts as a painless swelling and slowly develops into a poorly defined ulcer. If left untreated, these ulcers can expand from a small size to covering a large area. They are mostly reported from people in West Africa, Central and South America, Australia, and Japan.
In the case of pulmonary mycobacterial infection, patients with weakened lung defense mechanisms, such as those with cystic fibrosis, chronic obstructive pulmonary disease, HIV, and other immune deficiency conditions, are more prone. This type of infection also affects more men, especially those middle-aged or older with a history of alcohol and tobacco usage. Symptoms include cough, deteriorating respiratory function, pneumonia, blood while coughing, persistent fever, and weight loss. This type of infection generally shows rapid progression. However, a slow-progressing version of the disease with similar symptoms has been noted in women post-menopause or those with a lower BMI, scoliosis, or abnormalities in the rib cage.
Testing for Atypical Mycobacterial Disease
Detecting mycobacteria, a type of bacteria, through laboratory tests can be tricky. The first step in testing for most infections is a blood test known as a Complete Blood Count (CBC). This test might show a normal or slightly increased number of white blood cells. Other tests to check the level of inflammation in the body, such as C-reactive protein and erythrocyte sedimentation rate tests, can also show normal or slightly increased results.
For more specific results, samples from fluid cultures taken from affected soft tissues or lymph nodes should be subjected to a special type of stain, either acid-fast or fluorochrome. This helps identify the presence of the bacteria in around 30% to 60% of the cases. Moreover, cultures of these fluid and tissue samples can yield an organism in about 65% of the cases.
Patients with a widespread infection often have detectable bacteria in their blood, which can be observed in about 90% of cases. It’s important to note that the growth of mycobacteria in culture is slower than common bacteria. Rapidly growing mycobacteria will take about a week or more to grow, while slow-growing ones can take several weeks to months to show growth.
A test known as the Polymerase Chain Reaction (PCR) is often used for faster results. It’s a sensitive diagnostic tool that can identify the organism about 91% of the time. A skin test, known as tuberculin skin testing, can also help confirm a suspected atypical mycobacterial infection. This test results in a skin reaction larger than 10 mm in approximately 30% to 60% of the cases.
As for lung infections, the diagnosis is typically based on clinical suspicion of an active infection, which is normally informed by symptoms, chest X-ray or CT scan results, and growth on two or more sputum cultures. Tissue biopsy or lavage cultures are also sometimes used to help confirm the diagnosis.
Treatment Options for Atypical Mycobacterial Disease
Adults and children with MAC (Mycobacterium Avium Complex) infections are commonly treated with three types of antibiotics: azithromycin, rifampin, and ethambutol. Different dosages are used depending upon the type of illness. For example, adults with a specific type of lung disease may take doses of these drugs three times a week. However, if the illness is severe, daily dosages might be needed, with additional drugs like streptomycin or amikacin.
The antibiotics are usually continued until the patient has shown improvement for 12 months, measured by regular checks of their sputum (a mixture of saliva and mucus coughed up from the lungs). If the sputum test still shows signs of the disease after 12 months, or there’s no improvement in the patient’s condition after 6 months, the treatment may not be working. In severe situations, where a patient’s health continues to deteriorate, a surgical operation to remove affected parts of the lung might be necessary.
There’s an increase in resistance to treatment in certain types of MAC infections, making them more difficult to treat. As a result, different medications may sometimes be used, such as inhaled amikacin, clofazimine, and moxifloxacin.
There are other types of bacteria similar to MAC that can cause lung disease. These are typically treatable with a range of antibiotics. However, some, like Mycobacterium abscessus, are highly resistant to antibiotics. Often, the only cure for this type of infection is surgery, while untreated patients may be given intermittent antibiotic treatment to slow the disease’s progression.
When MAC infections affect the lymph nodes, a different treatment strategy is used. This usually comprises of two types of antibiotics, azithromycin or clarithromycin, combined with rifampin or ethambutol. The antibiotics are taken daily until symptoms disappear. In some cases, surgery may be used alongside antibiotic treatment to remove infected lymph nodes and tissues, resulting in significantly better cure rates.
Skin and soft tissue infections are dealt with through a combination of antibiotics, the selection of which may vary based on testing results. In severe cases where the infection impacts the tissues extensively, surgical removal of the dead tissue might be required.
What else can Atypical Mycobacterial Disease be?
Lymphadenitis, or swelling of the lymph nodes, can be caused by a variety of conditions. These might include tuberculosis, viral infections, cancers such as leukemia or lymphoma, or bacteria like Staphylococcus aureus. Additionally, a bacterial infection called Bartonella henselae can cause lymphadenitis.
- Tuberculosis
- Viral lymphadenitis
- Leukemia/Lymphoma
- Staphylococcus aureus or other bacterial abscesses
- Bartonella henselae
Certain skin and soft tissue conditions can also cause similar symptoms. These include infections caused by bacteria such as Staphylococcus aureus or Group A Streptococcus, the bacterium Pseudomonas, fungal infections, and a condition called sporotrichosis.
- Staphylococcus aureus or Group A Streptococcus
- Pseudomonas
- Fungal soft tissue infection
- Sporotrichosis
In the lungs, conditions like tuberculosis, fungal infections, or bacteria like Streptococcus pneumoniae and Staphylococcus aureus can cause disease. Pseudomonas, a type of bacteria, may cause infection, as can a number of malignancies (cancers). Viral pneumonia (lung inflammation caused by a virus) and autoimmune diseases (conditions where the body attacks itself) could also be the cause.
- Tuberculosis
- Fungal infection
- Streptococcus pneumoniae
- Staphylococcus aureus
- Pseudomonas
- Malignancy
- Viral pneumonia
- Autoimmune disease
What to expect with Atypical Mycobacterial Disease
Treatment of a lung disease called ‘Mycobacterium avium’ is successful for about 39% of patients. This disease has a 5-year mortality rate which is around 12%. When the strain of the disease is resistant to a certain kind of drugs known as macrolides, the illness becomes more serious. This results in a higher 5-year mortality rate of about 47%. Another lung infection called ‘Mycobacterium abscessus’ also has poor outcomes, with only about 41% of patients getting better after both surgical and antibiotic treatments. When only antibiotics are used, this rate drops to 34%.
When it comes to lymphadenitis (a type of infection in the lymph nodes) in children caused by Mycobacterium avium, using both surgical and antibiotic treatments can cure about 95% of cases.
For skin and soft tissue infections caused by bacteria such as Mycobacterium marinum, abscessus, ulcerans, and fortuitum, most patients recover once they receive proper antibiotic and surgical treatments.
Possible Complications When Diagnosed with Atypical Mycobacterial Disease
Mycobacterial lymphadenitis, an infection in the lymph nodes, may lead to several health issues. The infection itself can create an abnormal connection in the body, known as a fistula, and might require repeated surgeries. Since the lymph nodes in the neck and face are often affected, especially in young children, these surgical procedures can leave physical scars, causing the individual’s appearance to change. The impact this has on a person’s self-esteem and social life is also a concern.
When it comes to treatment, antibiotics alone can effectively treat 66% to 73% of cases. However, if surgery is included, the chances of recovery increase to about 95%.
On the other hand, treatment for those with multiple health issues and elderly patients can be challenging. For example, long-term antibiotic treatment or surgery may be difficult for these individuals to handle. Therefore, doctors might have to discuss whether long-term therapy to manage the symptoms or treatment aiming to cure the disease is more suitable.
- Clarithromycin, a type of antibiotic, can cause stomach upset and might need to be taken twice a day.
- Azithromycin can interfere with the heart rhythm and may be unsuitable if the patient is on certain medication.
- Rifabutin can cause a low white blood cell count and inflammation in the eyes.
- Ethambutol can cause inflammation in the optic nerve and eye exams should be carried out to check for loss of vision and colour blindness.
- Serious lung infections may require a part of the lung to be surgically removed (lobectomy). While this can cure the infection, it can also result in long term breathing problems.
Preventing Atypical Mycobacterial Disease
Getting treatment for skin and soft tissue infections from licensed medical providers can help avoid further health complications. This is particularly important for special groups of patients who have conditions like cystic fibrosis, HIV, or who have a weakened immune system. These patients should follow the treatment advice given by their specialist doctors to avoid getting additional infections that can take advantage of their weakened immune systems.
