Mycobacterium kansasii is the second most commonly occurring Non-Tuberculous Mycobacteria (NTM) in the United States. Infection is typically seen in middle aged males, and the risk of infection is greatly increased in immunocompromised hosts. Pulmonary infection presents in clinical parallel to that of Mycobaterium tuberculosis (TB) and is therefore often misdiagnosed. A combination of clinical, radiological, and microbiological evidence of infection is generally required to clinch the diagnosis. Treatment of such cases include prolonged courses of rifampin in combination with 2 other antimicrobial agents. The overall prognosis with appropriate treatment is good with the exception of disseminated disease in severely immunocompromised hosts. In patients who are misdiagnosed or undertreated, there is progressive destruction of the lung parenchyma with distortion of lung architecture. This can in-turn lead to bronchiectatic changes leaving the airways exposed to devastating superimposed bacterial pneumonia. We describe a case of a patient with untreated M. kansasii infection who developed superimposed necrotizing pneumonia and respiratory failure requiring prolonged ventilatory support.

Lung abscesses are most commonly polymicrobial, being caused by both anaerobic and aerobic bacteria, usually from the oral flora. A particular pathogen present in the oral flora, Streptococcus intermedius, has been known to cause aggressive pyogenic infections such as abscesses, most often on the soft tissues, liver and brain. Though less common, these infections can also occur in the lungs of immunocompetent individuals without preceding risk factors. In such cases, a presentation with productive cough and fever can be misdiagnosed as tracheobronchitis or pneumonia. We present the case of an immunocompetent patient without significant underlying risk factors, who was initially misdiagnosed as recurrent sinusitis, that was found to have a lung abscess due to S. intermedius infection.

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