TB Susceptibility

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Who gets TB?

Well, actually anyone can get TB. A lot of people do. Throughout history, it's been one of the biggest killers. It's estimated that 2 billion carry TB worldwide currently. 9 million develop active disease each year. 1.5 million die. As deaths from HIV drop, TB may surpass HIV as the number one infectious disease cause of death worldwide.

Some people are more at risk than others.

How does TB spread?

TB is almost always spread by breathing. Someone who carries the infection in their lung coughs, speaks, or just breathes. TB is released into the air. Someone else breathes it in. 

Crowded conditions without sunlight, fresh air or wind can lead to more rapid TB spread.

To prevent transmission, special masks (such as N95's) protect wearers from infection. Those who are infected can wear simple surgical masks to prevent some spread. UV light - such as outside from the sun or from UV light filters - can cut the spread. Turnover of air - from wind or from air filters in TB clinics - can also prevent transmission. 

Once TB infects someone, it doesn't mean that they have active disease. Some will go on quickly to develop active TB, but many will have latent TB, where TB is inside their bodies but is not causing illness. Such latent TB can be detected by tests like a PPD and treated with a drug like Isoniazid to prevent the development of active TB.

Some people are more at risk

Geography plays a large role in risk for TB. Some countries have much higher rates of TB. South Africa likely sees 1 in 100 develop active TB each year. Other countries see 3 in 1000 per year, while the US sees 3 in 100,000 develop TB in a year. Some locations within countries have more spread; some have more spread of drug resistant TB.

In the US, those at most risk for developing TB are those who were born abroad, especially in Asia, including the Indian sub-continent, Africa, Latin America and parts of Russia and the ex-Soviet Republics.

HIV creates a vulnerability for TB. Those who are infected are more likely to develop TB. Of the 9 million who develop TB each year, 1.1 million have HIV. The risk of developing TB when HIV infected is over 25x higher than among those who do not have HIV. Drug resistance and treatment failure can be more common as well. Many also have difficulty obtaining HIV medications required for a good outcome.

Immunosuppression from other causes can also create holes in the immune system that allow TB to develop. This can happen when someone has a an organ transplant, starts medications for Rheumatoid Arthritis or other autoimmune disorders, starts chemotherapy for cancer, or develops a blood cancer, like leukemia.

Diabetes also predispose some individuals to develop TB. Diabetes that is more difficult to control is tied to even more risk of developing TB.

Those with diabetes and TB are also more prone to failing treatment. There is a concern rising rates of diabetes may mean rising rates of TB.

Crowding creates an opportunity for TB to spread. Families may sleep close together; TB can spread from person to person in a room as they sleep huddled together. This is  also true for prisons, where healthcare may be difficult to obtain for some infected prisoners, especially in less-resourced, more crowded prisons. Those who are homeless may also be exposed in shelters or if living in outdoor, crowded conditions, especially if other risk factors (like malnutrition or HIV) are higher in this population. Likewise, those who work in crowded conditions and live in crowded dormitories, such as mine workers, can be at more risk.

Children - particularly infants - are at more risk for acquiring TB and for going on to develop disease. Unfortunately, when children become sick with TB, they often are not diagnosed. Their TB infection may be mistaken for other childhood illnesses or may be not recognized until too late.

Elderly are also at increased risk. Many grew up at a time and place where TB was more prevalent and so have silently carried latent TB. As they age and maybe develop more health problems, their immune systems cannot hold back TB and active infections develop.

Healthcare workers may be exposed to TB in their work. This can occur among healthcare providers who do not know that they work with TB patients. Those infected with active disease often do not know they are infected and may seek care in emergency departments or clinics and not be diagnosed until later (if at all, sadly in some cases). Depending on the level of TB in the community, healthcare workers develop latent TB at higher rates than others varying between 3.8% to 8.4% annually worldwide.

Silicosis can cause damage to the lungs as people breathe in silica. Those who work in mines may have lung damage that creates an opportunity for TB to flourish. Housing and work conditions may also lead to crowding and increased rates of HIV among those displaced from home for work. This has resulted in high rates of TB among mineworkers in South Africa, where 3 in 100 develop TB each year

Malnutrition can also lead to more TB. Those who do not eat enough may see their TB grow from latent to active.

Genetics make some more prone to developing TB than others. There are a number of genes responsible.

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