During the first week of his treatment, a positive BACTEC culture signal was observed in 1 of his sputum samples. After inoculation of the positive culture with p-nitro-acetylamino-hydroxypropiophenonone, it was recorded as “p-nitro-acetylamino-hydroxypropiophenonone-resistant Mycobacterium.” After subtyping with polymerase chain reaction, it was reported as M. fortuitum. His antibiotic regimen was switched with ciprofloxacin (1000 mg), clarithromycin (1000 mg), and trimethoprim sulfametoxazol (320/1600 mg), daily. Sensitivity studies showed that the organism was resistant to INH, rifampicin, pyrazinamide, ethambutol, streptomycin, oflaxacin, and canamycin, and was sensitive to capriomycin, ciprofloxacin, clarithromycin, and amikacin. A repeat CT scan in the first month of therapy showed a near-total resolution of the infiltrates. His treatment was continued for 12 months until the last negative sputum culture.
M. fortuitum is a ubiquitous, rapidly growing organism that can be found in soil, tap water, or dust. When isolated from human sources it usually reflects colonization rather than infection.2 It can cause skin and soft-tissue infections after penetrating trauma or punch biopsy.3 It has also been implicated in causing infections after thoracoabdominal surgeries and pacemaker insertions.4–6M. fortuitum has also been known to cause diffuse lymphadenitis.7
The respiratory infections with M. fortuitum are rare in an immunocompetent host and are mostly associated with underlying primary lung conditions, such as chronic obstructive pulmonary disease, cystic fibrosis, bronchiectasis, malignancies, or cavities from healed M. tuberculosis infection.8
Our case is unique in the fact that the patient was immunocompetent without any underlying primary lung condition. He was indeed an active smoker, yet was not known to have chronic obstructive pulmonary disease or its symptoms. On the basis of his radiologic studies, we doubt that his present illness was related to his latent M. tuberculosis infection. Positive BAL culture for S. vestibularis was most likely a contaminant. Reviewing the literature, we could not find any correlation between his travel and the infection. We suspect that our patient suffered with primary lung infection with M. fortuitum.
The isolation of all NTM species from a respiratory sample is insufficient evidence for establishing the diagnosis of the disease. One must rely on clinical, radiographic, and bacteriologic criteria as described in the American Thoracic Society guidelines to confirm the diagnosis.9 Our case fulfilled the criteria with positive sputum culture for M. fortuitum and the biopsy showed caseating granulomatous inflammation without AFB.
M. fortuitum isolates are susceptible to multiple oral antimicrobial agents, including macrolides, quinolones, doxycycline, minocycline, and sulfonamides. Drug susceptibilities for this species are important for guiding effective therapy.9 All isolates of M. fortuitum contain some resistance to macrolides. Thus, despite susceptible minimal inhibitory concentrations seen in 80% of the isolates for clarithomycin, macrolides should be used with caution. The treatment should include at least 2 agents with in vitro activity against the organism and should be continued for 12 months after the last negative sputum culture. The selection of the agent is usually dictated by the patient's tolerance.9
Mortality because of localized M. fortuitum infection is rare. Death may result from extensive pulmonary or disseminated disease in immunocompromised patients.10
In summary, primary lung infection from M. fortuitum is rare. Yet, it should be included in the differential diagnosis of lung infiltrates in an immunocompetent host. A high index of suspicion is required, particularly in patients with a travel history to countries with high endemic mycobacterial infections. Invasive procedures such as FB or TTNA may be required to confirm the diagnosis. Advanced bacteriologic studies help select appropriate treatment and achieve successful outcome.
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9. Griffith DE, Aksamit T, Brown-Elliott BA, et al; ATS Mycobacterial Diseases Subcommittee; American Thoracic Society; Infectious Disease Society of America. An official ATS/IDSA statement: diagnosis, treatment, and prevention of nontuberculous mycobacterial diseases. Am J Respir Crit Care Med. 2007;175:367–416.
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Keywords:© 2010 Lippincott Williams & Wilkins, Inc.
Mycobacterium fortuitum; nontuberculous mycobacteria; pneumonia; immunocompetent host