Tuberculosis causes a great burden of disease globally. There are an estimated 10 million cases of active T.B. in the world each year and approximately 1.5 million deaths. Cases of Tuberculosis in the United States are decreasing. The most considerable incidence in T.B. in the United States is from those born outside of the United States. Previously called consumption, Tuberculosis is caused by a group of similar bacteria called the M. tuberculosis complex. M. tuberculosis is the most significant cause of human disease from the M. tuberculosis complex. M. tuberculosis is an acid-fast bacterium. Respiratory droplet nuclei spread T.B.. The mycobacterium can live outside the body for 8-10 days. Although, there is no other transmission mode for T.B. beyond respiratory droplet nuclei. Direct contact with sputum is not known to transmit Tuberculosis. Humans are the only reservoir for T.B.. U.V. radiation/ light kills M. tuberculosis which may be related to evidence suggesting that more T.B. infections start in the winter months. However, lower sunlight during the winter months is also associated with lower vitamin D levels. And winter crowding could be the reason for increased initial infections with T.B. during the winter as well. Most cases of active Tuberculosis are pulmonary infections. Symptoms of active pulmonary T.B. include cough, hemoptysis, night sweats, fatigue, and weight loss. Active Tuberculosis has around a 50% case fatality rate without antibiotic therapy. Co-infection with HIV/ AIDS increases the risk of Multi-Drug Resistant T.B. infection. Additionally, T.B. makes AIDS progress faster. Some of the main extra-pulmonary tuberculosis sites of infection are the pleura, pericardium, meninges, bones, kidneys, and gastrointestinal tract. In other words, Tuberculosis can infect many different organs (bones, pleura, pericardium, the nervous system causing meningitis or tuberculoma, gastrointestinal system, and genitourinary system, as well as be in the form of miliary T.B. which is the spread of T.B. throughout the body. Fever of unknown origin can be from T.B.. Most people exposed to T.B. do not develop an infection. Of those who do become infected, 90% of the cases will be latent T.B. infections, and up to 10% will become active infections. Latent T.B. Infection is not infectious. Active cases of T.B. should be treated right away to limit spread to others. Antibiotic therapy needs to be multi-drug. Early treatment before cavity lesions develop, for example, often cures active tuberculosis cases. If treatment fails, then multiple other drugs need to be added. Administration of antibiotics for active cases of tuberculous should be by direct observation therapy if possible. Then sputum cultures are followed until a negative culture is seen. Sputum cultures are often collected on various timelines (sometimes monthly). For drug-susceptible T.B., treatment of active cases starts with an intensive 8-week treatment of 4 antibiotics (isoniazid, rifampin, pyrazinamide, and ethambutol). Followed by four to seven months of continuation treatment. Treatment of drug-resistant and multi-drug resistant T.B. is complicated and should be managed by a provider with experience managing drug-resistant and multi-drug resistant T.B. or through close consultation. Many of the medications for T.B. have significant side effects, such as hepatotoxicity. Transaminases should be checked if the patient is experiencing nausea or other signs or symptoms of liver dysfunction. In countries with high T.B. prevalence, vaccination with the B.C.G. vaccine is recommended at birth. Due to the low incidence of T.B. in the United States, B.C.G. vaccination is not recommended routinely in the U.S.. B.C.G. vaccination causes a positive Tuberculin Skin Test. The B.C.G. vaccine should not be used in persons with H.I.V. or in multiple others immune-comprised conditions. A contact investigation is conducted for contacts of active T.B. cases. A contact investigation for T.B. starts with contact tracing utilizing concentric circles, starting with household contacts. Contact investigation for T.B. also includes an assessment with examination and evaluation of contacts as well as starting treatment for those with active or latent t.b. infection. It takes both the I-GRA and T.B. Skin Tests around eight weeks to become positive following exposure and initial infection. This is known as the window period for T.B.. High-risk contacts may be treated with window period prophylaxis. Initial testing for T.B. can be done following a T.B. exposure, but additional final testing should be eight weeks after known exposure. The I-GRA tests are more specific than the Tuberculin skin tests are. The B.C.G. vaccine does not cause a false positive very often with the I-GRA test. T.B. Skin Test is recommended for Children less than five years of age. A positive T.B. Skin test is based on the size of skin induration. A 5-millimeter threshold is used for close contacts of individuals with active T.B.. A 5-millimeter threshold is also used for people with H.I.V. or who are otherwise immunosuppressed. A 10-millimeter threshold is used for people considered high risk and healthcare workers. A 15-millimeter threshold is used for people who are low risk. Quantiferon Gold or I-GRA is the preferred test in people with a history of B.C.G. vaccination. People at higher risk for T.B. infection should be tested for T.B. infection. People that should be tested for T.B. are:
5-10% of people with latent T.B. Infection will develop active T.B. at sometime in their lifetime. There are several treatment options for Latent T.B. Infection. Isoniazid/ I.N.H. daily for 6-9 months, rifampin daily for four months, isoniazid I.N.H. plus rifapentine weekly for three months, or isoniazid I.N.H. plus rifapentine daily at a lower dose than is given weekly for three months. Two-step T.B. Skin testing is recommended for new hire healthcare workers because sometimes a person will have untreated latent T.B. infection and still have a negative initial T.B. Skin test - if they were infected with latent T.B. a long time ago. In two-step T.B. Skin Testing, the second dose can be administered 1-3 weeks after the first (and no more than 12 months after the first). The I-GRA has the advantage of the patient not needing to follow up in 48-72 hours as is required to assess for the size of induration with the T.B. Skin test.
References:
Sultana, Z.Z., Hoque, F.U., Beyene, J. et al. HIV infection and multidrug resistant tuberculosis: a systematic review and meta-analysis. BMC Infect Dis 21, 51 (2021). https://doi.org/10.1186/s12879-020-05749-2
https://www.cdc.gov/tb/default.htm