eMedicine Specialties > Infectious Diseases > Mycobacterial Infections
Mycobacterium Kansasii
Updated: Mar 18, 2009
Introduction
Background
Mycobacterium kansasii is an acid-fast bacillus (AFB) that is readily recognized based on its characteristic photochromogenicity, which produces a yellow pigment when exposed to light. In 1953, Buhler and Pollack first described the bacterium. Under light microscopy, M kansasii appears relatively long, thick, and cross-barred.
The most common presentation of M kansasii infection is a chronic pulmonary infection that resembles pulmonary tuberculosis. However, it may also infect other organs. M kansasii infection is the second-most-common nontuberculous opportunistic mycobacterial infection associated with AIDS, surpassed only by Mycobacterium avium complex (MAC) infection. For this reason, the incidence of M kansasii infection has increased because of the HIV/AIDS epidemic.
Pathophysiology
Unlike other nontuberculous mycobacteria (NTM), M kansasii is not readily isolated from environmental sources. However, it has been isolated from a small percentage of specimens obtained from water supplies in areas with high endemicity. Most likely, M kansasii is acquired via either aspiration or local inoculation from the environment. Little evidence exists of person-to-person transmission. Molecular characterization of M kansasii shows that it is a homogeneous group of organisms. Five genotypes, or subtypes, are described. Types I and II are common clinical isolates, while the remaining types (III, IV, V) are recovered from environmental samples only. Type I probably is the most prevalent M kansasii isolate from human sources worldwide.
M kansasii infection of the lung causes a pulmonary disease similar to tuberculosis. Its histopathologic appearance is similar to that of tuberculosis and may include acute suppuration, nonnecrotic tubercles, or caseation. In persons with AIDS or in patients with other forms of immunocompromise, many of its characteristic histologic features may be absent.
After skin inoculation, M kansasii can cause local disease of the skin and subcutaneous tissue. It may spread from the local site and cause lymphadenitis, infection of a distant organ, or disseminated disease.
Frequency
United States
The prevalence of M kansasii, an unusual pathogen in the pre-AIDS era, has increased with the HIV pandemic. M kansasii is the second-most-common cause of NTM disease in patients with AIDS. M kansasii infection has typically been described as a disease of urban dwellers and of patients with high incomes and better standards of living. One study of 3 northern California counties found that M kansasii infection was more common in census tracts with a lower income (median income <$32,000). However, this study consisted of a large proportion of patients with HIV infection.1
M kansasii infection occurs throughout the United States, with the highest incidence in the Midwest and the Southwest. The study mentioned above, which was performed in northern California, estimated an overall incidence of 2.4 cases per 100,000 adults per year in the general population, 115 cases per 100,000 persons with HIV infection per year, and 647 cases per 100,000 persons with AIDS per year. This incidence of M kansasii infection is much higher than that determined by a national laboratory surveillance during 1982-1983, which estimated a prevalence of 0.3 cases per 100,000 persons.
International
M kansasii infection has been reported in most areas of the world. The incidence appears to be relatively high in England and Wales and among South African gold miners.2 In the United Kingdom, it has been reported as the most common cause of NTM lung infection in patients without HIV infection.3
An increasing incidence of NTM infections, including M kansasii, has been reported in other countries, including Israel, Korea, Portugal, France, and Japan.
Mortality/Morbidity
The likelihood of mortality associated with M kansasii infection depends on various factors, including the presence of comorbid diseases, treatment compliance, rifampicin use, and extent of infection. One US center's experience, which included 302 patients over more than a 50-year period (1952-1995), showed a mortality rate of 11%, but this included both immunocompromised and nonimmunocompromised patients.4
- A retrospective study of South African gold miners treated for M kansasii infection reported mortality rates of 2% in those without HIV infection and 9% in patients with HIV infection.2
- Untreated pulmonary M kansasii disease progresses and can lead to death in more than 50% of infected individuals.
Race
M kansasii infection has no reported racial predilection.
Sex
M kansasii infection is more common men, with a male-to-female ratio of 3:1.
Age
- M kansasii infection is more common in the older population and is rare in children.
- The age predilection shifts in conjunction with age predilections of HIV infection.
Clinical
History
In most cases, M kansasii causes lung disease that is clinically indistinguishable from tuberculosis. Symptoms may be less severe and more chronic than Mycobacterium tuberculosis infection. Asymptomatic M kansasii infection occurs in a small proportion (16%) of affected patients.4
- Healthy host
- The most common symptoms of pulmonary M kansasii infection include cough (91%), sputum production (85%), weight loss (53%), breathlessness (51%), chest pain (34%), hemoptysis (32%), and fever or sweats (17%).5
- Cutaneous M kansasii infection resembles sporotrichosis secondary to local lymphatic spread. Cutaneous lesions may include nodules, pustules, verrucous lesions, erythematous plaques, abscesses, and ulcers.
- Immunocompromised host
- M kansasii infection manifests late in the course of HIV disease. The lung is the organ most commonly involved. Commonly reported symptoms include fever, chills, night sweats, productive or nonproductive cough, weight loss, fatigue, dyspnea, and chest pain.
- Almost 20% of patients with HIV infection who develop M kansasii infection eventually develop disseminated disease.
- M kansasii meningitis similar to M tuberculosis meningitis has been reported in patients infected with HIV and may carry a higher mortality rate despite appropriate antibiotic therapy.
- M kansasii bacteremia, pericarditis with cardiac tamponade, oral ulcers, chronic sinusitis, osteomyelitis, and scalp abscess have been reported in patients with AIDS.
- Disseminated M kansasii infection has also been reported in other immunocompromised hosts (eg, patients with myelodysplastic syndrome, patients on hemodialysis).
- Cutaneous M kansasii infections in immunocompromised hosts usually have atypical clinical features (eg, cellulitis, seroma). These features, along with atypical histology (eg, absence of granuloma), may delay diagnosis.
Physical
- Common physical findings of M kansasii infection include the following:
- Fever
- Pulmonary crackles and wheezing
- Lymphadenopathy
- Analysis of a series of 49 patients coinfected with HIV showed the following physical findings at the time of initial isolation of M kansasii:6
- Pulmonary disease
- Fever (45%)
- Lung crackles (40%)
- Lymphadenopathy (25%)
- Wheezes (20%)
- Hepatosplenomegaly (5%)
- Disseminated disease
- Fever (60%)
- Hepatosplenomegaly (40%)
- Lung crackles (25%)
- Lymphadenopathy (10%)
- Cutaneous lesions (10%)
- Wheezes (5%)
- Pulmonary disease
- Patients with cutaneous M kansasii infection may develop nodules, pustules, verrucous lesions, erythematous plaques, abscesses, or ulcers.
- Other signs depend on the site of infection or dissemination.
Causes
Immunocompromised patients, including patients with HIV/AIDS, are at a high risk for M kansasii infection.
- Predisposing conditions for M kansasii infection include pulmonary conditions resulting from pneumoconioses (especially silicosis, gold mining, and coal mining), healed chronic infections (eg, tuberculosis, mycosis, chronic obstructive pulmonary disease, bronchiectasis), heavy smoking, and chronic obstructive pulmonary disease.
- Other risk factors include cancer, diabetes mellitus, long-term steroid use, alcoholism, peptic ulcer disease, coronary artery disease, and prior pneumonia.
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References
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Fishman JE, Schwartz DS, Sais GJ. Mycobacterium kansasii pulmonary infection in patients with AIDS: spectrum of chest radiographic findings. Radiology. Jul 1997;204(1):171-5. [Medline].
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Further Reading
Keywords
Mycobacterium kansasii, M kansasii, acid-fast bacillus, AFB, nontuberculous mycobacterial infection, NTM infection, AIDS, Mycobacterium avium complex, MAC, M kansasii chronic pulmonary disease, pulmonary tuberculosis, cutaneous M kansasii infection, M kansasii nodule, M kansasii pustule, M kansasii verrucous lesion, M kansasii erythematous plaque, M kansasii abscess, M kansasii ulcer, M kansasii bacteremia, M kansasii pericarditis, M kansasii oral ulcer, chronic M kansasii sinusitis, M kansasii osteomyelitis, M kansasii scalp abscess
