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Lung Infections & Tuberculosis

Infections of the lungs range from common community-acquired pneumonia to tuberculosis and fungal infections. Understanding when to seek evaluation and how these conditions are treated is important for protecting lung health.

Tuberculosis

Tuberculosis (TB)

TB is caused by Mycobacterium tuberculosis, a slow-growing bacterium spread through airborne droplets. It remains one of the leading infectious causes of death worldwide, though it is curable with appropriate treatment.[1]

Latent TB vs. active TB

  • Latent TB infection (LTBI): The bacteria are present but dormant. The person is not sick, has no symptoms, and is not contagious. However, latent TB can reactivate into active disease, especially if the immune system weakens.
  • Active TB disease: The bacteria are multiplying and causing symptoms — typically chronic cough (≥2–3 weeks), hemoptysis, night sweats, fever, unintentional weight loss, and fatigue. Active pulmonary TB is contagious.[1]
  • Approximately 5–10% of people with untreated LTBI will develop active TB at some point in their lives, with highest risk in the first 2 years after infection.
  • Higher risk of reactivation: HIV/AIDS, immunosuppressive therapy (TNF inhibitors, chemotherapy, transplant medications), diabetes, chronic kidney disease, malnutrition, and recent TB exposure.

Screening and diagnosis

  • Screening tests (for latent TB): Tuberculin skin test (TST/PPD) or interferon-gamma release assay (IGRA — QuantiFERON or T-SPOT). These detect immune response to TB but cannot distinguish latent from active disease.
  • Who should be screened: People born in or who have traveled to high-prevalence countries, healthcare workers, people with HIV, close contacts of active TB cases, immunosuppressed individuals, and those entering congregate settings.
  • Diagnosing active TB: Chest X-ray or CT (upper lobe cavitary lesions are classic), sputum AFB smear and culture, and nucleic acid amplification testing (NAAT/GeneXpert) for rapid detection. Culture remains the gold standard and is needed for drug susceptibility testing.[1]
  • Isolation: Patients with suspected active pulmonary TB are placed in airborne isolation precautions until infectiousness is ruled out or adequately treated.

Treatment of latent TB

  • Treating LTBI prevents reactivation. Preferred short-course regimens include 3 months of weekly isoniazid + rifapentine (3HP), or 4 months of daily rifampin (4R).[1]
  • Older regimen: 6–9 months of daily isoniazid (still used but less preferred due to longer duration and lower completion rates).
  • Vitamin B6 (pyridoxine) supplementation is given with isoniazid to prevent peripheral neuropathy.
  • Liver function monitoring during treatment, especially for patients with baseline liver disease, alcohol use, or age >35.

Treatment of active TB

  • Standard regimen: 2 months of intensive phase (isoniazid + rifampin + pyrazinamide + ethambutol), followed by 4 months of continuation phase (isoniazid + rifampin). Total: 6 months minimum for drug-susceptible TB.[1]
  • Directly observed therapy (DOT): Recommended to ensure treatment completion and prevent drug resistance.
  • Drug-resistant TB: Multidrug-resistant TB (MDR-TB) requires longer, more complex regimens with second-line drugs. Extensively drug-resistant TB (XDR-TB) is even more challenging to treat.
  • Monitoring: Monthly sputum cultures until conversion, regular liver function tests, vision screening (ethambutol), and symptom assessment.
  • Public health reporting: Active TB is a reportable disease. Public health departments assist with contact tracing and treatment supervision.
Pneumonia

Community-acquired pneumonia

Pneumonia is an infection that inflames the air sacs (alveoli) in one or both lungs. It can range from mild illness to life-threatening disease, particularly in older adults, young children, and people with weakened immune systems.[2]

Symptoms and evaluation

  • Cough (often with mucus), fever, chills, shortness of breath, chest pain with breathing, fatigue
  • Diagnosis typically involves chest X-ray, basic blood work, and sometimes sputum culture or blood cultures
  • Severity scoring (CURB-65, PSI) helps determine whether outpatient treatment is safe or hospitalization is needed
  • CT chest may be needed for complicated cases, pleural effusion evaluation, or when standard imaging is unclear

Treatment and prevention

  • Bacterial pneumonia: Treated with antibiotics — outpatient (amoxicillin, doxycycline, or a macrolide) or inpatient (IV antibiotics based on severity)[2]
  • Viral pneumonia: Influenza pneumonia may be treated with oseltamivir; COVID-19 pneumonia has specific antiviral and immunomodulatory treatments
  • Prevention: Pneumococcal vaccines (PCV20 or PCV15 + PPSV23), annual influenza vaccination, COVID-19 vaccination, RSV vaccination for eligible groups, hand hygiene, and smoking cessation
  • Recovery: Radiographic improvement often lags behind clinical improvement. Full recovery may take weeks to months, especially in older adults.
Fungal Infections

Fungal lung infections

Several fungi can infect the lungs, particularly in certain geographic regions or in immunocompromised patients.

Endemic mycoses
  • Histoplasmosis: Caused by Histoplasma capsulatum, found in soil enriched with bird or bat droppings. Endemic in the Ohio and Mississippi River Valleys. Most infections are self-limited; severe or disseminated disease requires antifungal treatment (itraconazole or amphotericin B).
  • Coccidioidomycosis (Valley fever): Caused by Coccidioides immitis/posadasii, found in the desert Southwest US and parts of Central/South America. Often self-resolving, but can cause chronic pulmonary disease or disseminate in immunocompromised patients.
  • Blastomycosis: Caused by Blastomyces dermatitidis, found in the Great Lakes region and Ohio/Mississippi River Valleys. Can mimic pneumonia or lung cancer on imaging.
Aspergillus and opportunistic fungi
  • Aspergillosis: Aspergillus species can cause allergic bronchopulmonary aspergillosis (ABPA) in asthmatics, chronic pulmonary aspergillosis in patients with pre-existing cavities, or invasive aspergillosis in severely immunocompromised patients.
  • Pneumocystis pneumonia (PCP): Caused by Pneumocystis jirovecii, primarily in patients with severely compromised cellular immunity (HIV with very low CD4 counts, transplant recipients). Treated with trimethoprim-sulfamethoxazole.
  • Cryptococcus: Can cause pneumonia or meningitis, particularly in HIV/AIDS patients.

Related topics

Trusted resources

References

  1. Nahid P, Dorman SE, Alipanah N, et al. Official American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America clinical practice guidelines: treatment of drug-susceptible tuberculosis. Clin Infect Dis. 2016;63(7):e147-e195. doi:10.1093/cid/ciw376
  2. Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia: an official ATS/IDSA clinical practice guideline. Am J Respir Crit Care Med. 2019;200(7):e45-e67. doi:10.1164/rccm.201908-1581ST