What microorganisms cause pulmonary cavitation in adults, particularly those with compromised immune systems or underlying respiratory conditions?

Microorganisms Causing Pulmonary Cavitation

The most common infectious causes of pulmonary cavitation are Mycobacterium tuberculosis, anaerobic bacteria (particularly in aspiration settings), Staphylococcus aureus, gram-negative organisms (Klebsiella, Pseudomonas, E. coli), and fungi (Aspergillus, endemic fungi like Histoplasma, Coccidioides, and Blastomyces). 1, 2

Bacterial Pathogens

Mycobacterium tuberculosis

• Tuberculosis is the single most common cause of chronic pulmonary cavitation worldwide and should be considered in all patients with cavitary disease, particularly those with foreign birth from endemic areas, alcoholism, elderly nursing home residents, or immunocompromise 1
• Nontuberculous mycobacteria also cause chronic cavitary disease, mimicking tuberculosis clinically and radiographically 2

Anaerobic Bacteria

• Anaerobes are recovered in 79% of cavitating pulmonary infections, often as the sole pathogen (43% of cases) 3
• The predominant species include Fusobacterium nucleatum, Bacteroides melaninogenicus, Bacteroides fragilis, and Peptostreptococcus 3
• Aspiration pneumonia with anaerobes should be suspected in patients with poor dentition, neurologic illness, impaired consciousness, or swallowing disorders 1
• Risk factors include alcoholism, seizure disorders, and conditions predisposing to aspiration 1

Staphylococcus aureus

• S. aureus, particularly MRSA, causes cavitary pneumonia especially in patients with diabetes mellitus, head trauma, ICU admission, or healthcare-associated infections 1
• Hospital-acquired and ventilator-associated pneumonia with S. aureus frequently presents with cavitation 1

Gram-Negative Bacteria

• Klebsiella pneumoniae, Pseudomonas aeruginosa, and E. coli can all cause necrotizing cavitary pneumonia 1, 4
• Klebsiella is classically associated with thick-walled cavities and is more common in diabetics and alcoholics 4
• Pseudomonas aeruginosa should be considered in patients with bronchiectasis, late-onset hospital-acquired pneumonia (≥5 days), or healthcare-associated risk factors 1
• E. coli causing cavitary pneumonia is rare but reported in patients with uncontrolled diabetes 4
• Legionella species can cause cavitary disease and should be tested for using urinary antigen assay when epidemiologic features suggest exposure (cruise ships, water systems) 1, 5

Fungal Pathogens

Aspergillus Species

• Chronic cavitary pulmonary aspergillosis (CCPA) requires ≥3 months of symptoms with cavitation, pleural thickening, or fungal ball formation 1
• Aspergillus IgG antibody is the most sensitive microbiological test for CCPA 1
• CCPA typically occurs in patients with minimal immunocompromise and underlying pulmonary disorders 1
• CT imaging is particularly sensitive for detecting small nodular or cavitary lesions in immunocompromised patients 1

Endemic Fungi

• Histoplasma, Coccidioides, Blastomyces, and Paracoccidioides all cause chronic cavitary disease that mimics tuberculosis 1, 2
• These should be considered based on geographic exposure and travel history 1, 2
• Endemic fungi are less commonly identified than bacterial pathogens but remain important diagnostic considerations 1

Special Populations and Pathogens

Immunocompromised Hosts

• Pneumocystis jirovecii can cause cavitary disease in AIDS patients, though cavitation may be misdiagnosed by bronchoalveolar lavage alone 6
• Rhodococcus equi causes chronic cavitary disease in immunocompromised patients 2
• Fungal infections (Aspergillus, Cryptococcus) are more prevalent in immunocompromised patients and require bronchoscopy for diagnosis 1

Healthcare-Associated Infections

• Multidrug-resistant pathogens (MRSA, Pseudomonas, Acinetobacter, resistant Klebsiella) are more common with recent antibiotic use within 90 days, hospitalization ≥5 days, or healthcare facility residence 1
• Nursing home residents have pathogen spectra resembling late-onset hospital-acquired pneumonia, with S. aureus (29%), enteric gram-negatives (15%), and Pseudomonas (4%) 1

Critical Diagnostic Pitfalls

• Cavitation within consolidation may represent pulmonary infarction rather than infection, particularly in immunocompromised patients with risk factors for thromboembolism 7
• Isolation of Candida species, enterococci, viridans streptococci, or coagulase-negative staphylococci from respiratory specimens should rarely be considered causative pathogens 1
• Burkholderia pseudomallei (melioidosis) and Paragonimus westermani (paragonimiasis) are geographically restricted causes of cavitary disease that require specific travel history 2
• Polymicrobial infections are increasingly common, especially in ARDS patients, with rates of anaerobic-aerobic mixed infections approaching 79% 1, 3