6. Describe the offending organism, its morphological, cultural characteristics and their normal habitat.

• Slim rod
• acid-alcohol fastness
• fluoresces bright orange-yellow against a dark background with flourochrome stain
• Aerobic
• growth slow 3-6 weeks to be visible in standard media
• Bactec radiometric system detects growth in 7-16 days.
• Resistant to desiccation
• heat sensitive
• Intracellular and extracellular

7. How do these organisms gain access to humans?

• By inhalation of droplets generated by infected person while coughing.

8. How do they invade and spread in humans? What is the pathogenesis of M. tuberculosis infection in this patient? Is this a primary or reactivation infection? How might the patient have acquired the primary infection?

Primary infection :

• The patient inhales M. tuberculosis on droplet nuclei,  transmitted from an infected patient. 

• The organism is phagocytosed by alveolar macrophages. 

• Bacterial multiplication continues, destroying the macrophage, Lymphocytes and monocytes are attracted to the focus and monocytes are differentiated into macrophages which ingest bacilli. 

• Infected macrophages are carried to lymph nodes and may spread throughout the body. 

• Some bacilli spread through the blood stream to distant tissues

• In most within 2 weeks cell mediated immunity arrests further progression

• In minority it can progress to disease state (Pneumonia, Meningitis, Miliary tuberculosis)

• PPD becomes positive

Secondary infection:

• The patient has reactivated a focus of infection which was acquired in the past. This is not a new infection

• This occurs  when the cell mediated immunity fails due to any reason 

• Reactivation occurs at sites with high 02 tension (in the apices of lungs)  or because of deficient lymph production. 

• Most of the clinical disease is secondary reactivation

Our patient has disease in the typical location. Alcoholism, homelessness and living in shelter are the probable reasons for activation of his disease.

9. What type of infection does this patient have?

• Secondary (reactivation) infection

10. What defenses humans have against these organisms?

• These are intracellular organism
• Cell mediated immunity is the primary defense

11. How do these organisms able to overcome human defenses?

• Ability to multiply in activated macrophages
• To survive low pH, high lactic acid and high CO2

12. What is the end result of this battle between organisms and humans?

• Granulomas is the hallmark of tuberculous infection.
• Caseation necrosis

13. How do you diagnose this infection?

• AFB stain of concentrated sputum 
• Culture of sputum or fluids or tissue
• Biopsy demonstrating granulomas with organisms
• Suggestive radiological exams

Our patient has the compatible clinical history, CXR and demonstrable organism in sputum smear. You should send the sputum for culture and sensitivity studies.

14. What will be your therapeutic strategy? . Propose a treatment regimen for this patient.

• Four drugs: isoniazid, rifampin, ethambutol, pyrazinamide for 3 months followed by INH and Rifampin for 6 months. 
• Directly observed therapy (DOT) with above 4 drugs for two weeks, then 2x or 3x weekly DOT for six months.

15. How can you prevent it from spreading to others? Prevent its occurrence?   How is this infection spread? How do you prevent the spread of this infection while the patient is hospitalized?

The infection is spread by droplet nuclei generated from a person who is coughing. The nuclei are inhaled. The infection is prevented by 

• Covering the mouth of an infected person during coughing. 

• Respirators (masks) used by health care providers while caring for the patient

• Gowns and gloves

• Negative pressure isolation rooms and UV lights in the rooms

• Part of prevention is suspecting infection in high risk patients and keeping them in isolation if they have a compatible clinical picture

  • Hospitalization when there is a medical need 

  • Home confinement for not needing hospital care

  • Isolation is required for a period of two weeks on antituberculous therapy

Isoniazid should be prescribed for prevention of infection to PPD positive patients

• with no demonstrable disease state 

• who are at a high risk for activation

• with less risk for developing  INH induced hepatitis

16. What are other clinical infections with these organisms?

It can practically infect any organ. Common clinical infections are

• Pulmonary
• Meningitis
• Miliary tuberculosis
• Pelvic inflammatory disease
• Bone (Pott's disease of spine) and joints