Mycobacterium Tuberculosis

 

 

Overview (Microbiological Features and Global Epidemiological Situation)

Tuberculosis (TB) is caused by Mycobacterium tuberculosis. It is a non-motile obligate aerobe 2-4 micrometer in length. It has an unique cell wall mainly consists of mycolic acids, a major and specific lipid components of the mycobacterial cell wall, that has a remarkable architecture and impermeability. Although TB is a treatable and curable disease, it is one of the top 10 causes of death worldwide. In 2016, it is estimated that more than 10 million people fell ill with TB, and 1.7 million died from the disease, including 0.4 million among HIV positive people, according to the WHO report. 64% of the total derived from seven countries, India, Indonesia, China, Philippines, Pakistan, Nigeria, and South Africa.

Drug-resistant TB, including multi drug resistant TB (MDR-TB) or extensively drug-resistant TB (XDR-TB) is a persistent threat. In 2016, there were 60,000 new cases with resistance to rifampicin, the most effective first-line anti-TB drug, 490,000 cases of them were MDR-TB, and 6.2% of MDR-TB cases had XDR-TB, according to the estimation by WHO. Nearly half of the global MDR-TB cases derived from three countries, China, India and Russian Federation. [1] [2] [3]


Image: CDC, Public Health Image Library (PHIL)

Transmission Route

The pathogenic bacteria, Mycobacterium tuberculosis is transmitted through air and not by surface contact. When a person with pulmonary or laryngeal TB disease sneezes, sings, shouts or coughs, the infectious droplets nuclei containing the tubercle bacilli can be released into the air, which may remain in the air for several hours. Infection occurs when an individual inhales the droplet nuclei containing the bacteria. It traverses through the mouth, nasal cavity, upper respiratory tract and bronchi then reach the alveoli of the lungs where tubercle bacilli multiply. A small percentage enter the bloodstream and can be transported to other parts of the body, such as brain, bone, kidney, lung or larynx.

There are several factors that affects the Mycobacterium tuberculosis transmission, such as infectiousness of the person with TB disease (the number of tubercle bacilli that he/she expels into the air), exposure (proximity, duration and frequency), immune status of the exposed individual and environmental factors such as ventilation, concentration of infectious droplet nuclei, or air circulation.[4][5]

Symptom

Symptoms of TB disease depend on where the bacteria, Mycobacterium Tuberculosis, settles in the body. Usually the inhaled bacteria settle and grow in the lungs (pulmonary TB) and may cause symptoms such as, persistent coughing (3 weeks or longer), chest pain, coughing up blood/sputum. Symptoms of TB disease when the bacteria settle and grow in other parts of the body, such as kidney, spine, and brain, depend on the area affected by the bacteria. Other than those, general symptoms are weakness, weight loss, fever, and night sweats.

People with latent TB infection (LTBI) do not have symptoms and cannot spread the TB to others (they are not regarded as a TB case). However, they may develop TB disease in the future as the bacteria are present in their bodies. [5] [6]

Prevention Methods in Healthcare Facilities

According to CDC, a TB infection control program is based on the three levels of hierarchy, Administrative, Environmental and Respiratory-protection controls.

Administrative controls are regarded as the first and most important level. It aims to reduce the risk of exposures to persons suspected of having TB disease, which include; conducting TB risk assessment of the health-care setting, develop and institute a written plan of TB infection control, and training and educating health care workers, etc.

The second level control, Environmental controls are aiming to prevent the spread and reduce the concentration of infectious droplet nuclei in the environment by using ventilation (natural or mechanical), HEPA (High efficiency particulate air) filtration or UVGI (Ultraviolet germicidal irradiation).

Lastly, the third level control is the Respiratory protection controls. It aims to reduce the risk of exposure to infectious droplet nuclei in the air, which include, implementing respiratory-protection program, training health care workers on respiratory protection and also training patients on respiratory hygiene and importance of cough etiquette, etc. [6] [7]

Reference List

Hedia Marrakchi, M.-A. L. a. M. D., 2014. Mycolic Acids: Structures, Biosynthesis, and Beyond, s.l.: Chemistry& Biology 21, January 16, 2014.

WHO, 2018. Tuberculosis Fact sheet. [Online]
Available at: http://www.who.int/mediacentre/factsheets/fs104/en/ [Accessed 8 Mar 2018]

WHO, 2017. GLOBAL TUBERCULOSIS REPORT 2017, Geneva: WHO.

CDC Division of Tuberculosis Elimination, 2016. Core Curriculum on Tuberculosis: What the Clinician Should Know. [Online]
Available at: https://www.cdc.gov/tb/education/corecurr/ [Accessed 9 Mar 2018]

CDC Division of Tuberculosis Elimination, 2011. Tuberculosis / Publications & Products / Fact Sheets / General. [Online]
Available at: https://www.cdc.gov/tb/publications/factsheets/general/tb.htm [Accessed 9 Mar 2018]

CDC Division of Tuberculosis Elimination, 2016. Tuberculosis / Basic TB Facts. [Online]
Available at: https://www.cdc.gov/tb/topic/basics/default.htm [Accessed 9 Mar 2018]

CDC, 2005. Guidelines for preventing the transmission of mycobacterium Tuberculosis in health care settings, Atlanta, GA 30333: CDC.