Pulmonary Tuberculosis Overview

Tuberculosis (TB) is a worldwide health issue, especially in developing countries.
TB is a public health problem with medical and social implications, highlighting social welfare.
In Egypt, TB incidence was 12 cases per 100,000 in 2019, with half being smear-positive cases.
In 2000, annual incidence was 20 per 100,000.

Suspected TB: Any patient with a cough for at least 2 weeks accompanied by fever, weight loss, and night sweats.
Confirmed TB (Smear-Positive): Two positive sputum samples for acid-fast bacilli (AFB) by direct microscopic examination.
- Alternatively, one positive sputum sample with radiographic abnormalities consistent with active TB (determined by a physician).
- Or, one positive sputum sample and a positive AFB culture.
Confirmed TB (Smear-Negative): Individuals with TB symptoms, at least three negative sputum smears for AFB, and radiographic abnormalities consistent with active TB (determined by a physician), followed by treatment with anti-TB therapy.
- Alternatively, a positive AFB culture with a negative sputum smear.
Confirmed Extrapulmonary TB: A patient with a positive AFB culture from an extrapulmonary site or histological evidence of active extrapulmonary TB, followed by treatment with anti-TB therapy by a physician.

TB is more common in developing countries but emerging in developed countries.
Distribution is generally uniform within countries, but more prevalent among slum dwellers and low-income urban populations.

TB mortality and morbidity decreased in mid-20th century due to better living conditions and improved antimicrobial therapy.
Re-emergence of TB in the 1990s due to:
- Poor TB control program performance, leading to disease spread.
- Poor program management, resulting in drug-resistant strains of Mycobacterium tuberculosis.

Cultural Characters:
- Obligate aerobes.
- Optimum growth temperature: 37°C for 2 to 8 weeks.
- Grow on media containing organic substances, including:
  - Dorset egg and egg saline (enriched media).
  - Lowenstein-Jensen (LJ) media (selective media) containing malachite green to inhibit other bacteria.
Sensitivity to Physical and Chemical Agents:
- Killed by moist heat for 15-20 minutes at 60°C.
- Susceptible to sunlight and ultraviolet rays.
- More resistant to chemical agents compared to other bacteria, including malachite green and antibiotics like penicillin.
- Resistant to acid and alkali (used for specimen decontamination).
- Resistant to drying and 5% phenol for several hours.

Reservoir of Infection:
- Human type: Cases of pulmonary TB with positive AFB sputum.
- Bovine type: Infected cattle.
Source of Infection:
- Human type: Respiratory secretions from a TB patient excreting large amounts of AFB.
- Bovine type: Unpasteurized milk from infected cattle.
Exit Portal:
- Human type: Respiratory tract (nose and mouth).
- Bovine type: Udder of infected cattle (released in milk).
Entry Portal:
- Human type: Nose and mouth.
- Bovine type: Mouth.
Modes of Transmission:
- Contact:
  - Droplet transmission.
  - Less commonly, indirect contact with contaminated objects (fomites or dishes).
- Airborne:
  - Droplet nuclei.
  - Dust nuclei.
- Common vehicle: Unpasteurized milk and dairy products.

Period of Communicability:
- Moderate communicability (secondary attack rate of 48%).
- Untreated patients are infectious.
- Effective treatment reduces infectivity by 90% within 48 hours.

General susceptibility.
Individuals with factors predisposing them to infection and disease development are at a higher risk.
Immunity is cell-mediated, relying on cellular proliferation.
Immunity can be acquired through:
- Natural active immunity following infection.
- Artificial active immunity through BCG vaccination.

Pathogenesis:
- Inhaled droplets containing mycobacteria reach the alveoli upon exposure.
- Spread through direct extension, lymphatic channels, and bloodstream (bovine TB through milk ingestion causing intestinal TB).
- Mycobacteria reside intracellularly within macrophages and cells of the reticuloendothelial system.
- Alveolar macrophages phagocytize mycobacteria, but in many cases, mycobacteria prevent phagosome-lysosome fusion, preventing intracellular killing.
- In response, macrophages secrete IL-12 and TNF-α, triggering a cell-mediated immune response.
- This response recruits T cells and NK cells to the infected area, leading to T-cell differentiation into TH1 cells and subsequent IFN-γ secretion.
Primary Infection:
- First contact with mycobacteria.
- Leads to an acute exudative lesion in the lungs spreading to lymphatics and regional lymph nodes (Gohn's complex).

Antiviral medications are used to prevent or treat influenza virus infection.
Recommended for:
- Early-stage influenza patients (within 48 hours of illness onset).
- Patients with high risk of complications:
  - Asthma, chronic lung disease, diabetes, heart disease, morbid obesity, individuals 65 years and older.
- Patients requiring hospitalization for severe or complicated illness.

Types: Oseltamivir, zanamivir, and peramivir.
Effectiveness: Against influenza A and B viruses
- Oseltamivir: Oral prodrug activated by hepatic esterases, distributed throughout the body.
- Zanamivir: Inhaled, directly to the respiratory tract.
- Peramivir: Intravenous (single dose).
Mechanism of Action:
- Competitive, reversible inhibition of the enzymatic action of influenza neuraminidase.
- Neuraminidase is required of release of the virus from infected cells.
- Inhibition leads to viral aggregation at the cell surface, preventing infection spread.
Therapeutic Uses:
- Treatment of acute, uncomplicated influenza A or B infections.
- Oral oseltamivir and inhaled zanamivir can prevent Influenza A and B infections.