Tuberculosis (TB) Part 5

Tuberculosis (TB) is the number one infections disease killer worldwide. The World Health Care Organization estimates that 2 billion people have latent TB, while another 3 million people worldwide die each year due to TB.

On average, the isoniazid (INH) resistance rate is approximately 10% and the rifampin resistance rate is approximately 1%, with lower numbers in countries with good TB programs and higher numbers in the countries with poor TB programs.

Humans are the only known reservoir for Mycobacterium tuberculosis. TB is transmitted by airborne droplet nuclei, which may contain fewer than 10 bacilli. Exposure to TB occurs by sharing common airspace with a patient who is infectious. When inhaled, droplet nuclei are deposited within the terminal airspaces of the lung. Upon encountering the bacilli, macrophages ingest and transport the bacteria to regional lymph nodes.

Special Concerns:

" Pregnancy
o Pregnancy provides an opportunity to screen for TB; all pregnant mothers can have tuberculin skin testing performed. If skin testing results are positive, a chest radiograph can be obtained with lead shielding (the amount of radiation exposure of a single chest radiograph has been compared to that incurred on a regular flight from New York to Los Angeles). The chest radiograph should not be delayed during the first 3 months of pregnancy if the patient has symptoms.

o Treatment for active TB should be initiated even during the first 3 months of pregnancy. INH, rifampin, and ethambutol may be used. Pyrazinamide should be used only in women infected with HIV who are suspected of having MDR-TB.

o In most pregnant women, preventive treatment should be delayed until 2-3 months after delivery, even through no harmful effects of INH on the fetus have been documented. Consider preventive treatment during pregnancy in the following situations.
" Pregnant women with a positive tuberculin skin test who are HIV seropositive or who have behavioral risk factors for HIV infection but decline HIV testing.
" Pregnant women with a positive tuberculin skin test who have in close contact with a patient who is smear-positive for pulmonary TB.
" Pregnant women who have had a documented tuberculin skin test conversion in the past 2 years.

o To reduce the risk of peripartum hepatitis, preventive treatment should not be given for the intial 2-3 months after delivery. Breastfeeding can be continued while on preventive therapy. Whether the breastfeed infant should receive pyridoxine is controversial.

Humans are the only known reservoir for Mycobacterium tuberculosis. TB is transmitted by airborne droplet nuclei, which may contain fewer than 10 bacilli. Exposure to TB occurs by sharing common airspace with a patient who is infectious. When inhaled, droplet nuclei are deposited within the terminal airspaces of the lung. Upon encountering the bacilli, macrophages ingest and transport the bacteria to regional lymph nodes.

Dr. D.S. Merchant Resident Medicine AKUH
Gold Medalist (Anatomy & Histology)
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