TB Risk Factors

Some people develop TB disease soon after becoming infected (within weeks) before their immune system can fight the TB bacteria. Other people may get sick years later, when their immune system becomes weak for another reason.

Overall, about 5 to 10% of infected persons who do not receive treatment for latent TB infection will develop TB disease at some time in their lives. For persons whose immune systems are weak, especially those with HIV infection, the risk of developing TB disease is much higher than for persons with normal immune systems.

Generally, persons at high risk for developing TB disease fall into two categories:

• Persons who have been recently infected with TB bacteria
• Persons with medical conditions that weaken the immune system

Persons who have been Recently Infected with TB Bacteria

This includes:

• Close contacts of a person with infectious TB disease
• Persons who have immigrated from areas of the world with high rates of TB
• Children less than 5 years of age who have a positive TB test
• Groups with high rates of TB transmission, such as homeless persons, injection drug users, and persons with HIV infection
• Persons who work or reside with people who are at high risk for TB in facilities or institutions such as hospitals, homeless shelters, correctional facilities, nursing homes, and residential homes for those with HIV

Persons with Medical Conditions that Weaken the Immune System

Babies and young children often have weak immune systems. Other people can have weak immune systems, too, especially people with any of these conditions:

• HIV infection (the virus that causes AIDS)
• Substance abuse
• Silicosis
• Diabetes mellitus
• Severe kidney disease
• Low body weight
• Organ transplants
• Head and neck cancer
• Medical treatments such as corticosteroids or organ transplant
• Specialized treatment for rheumatoid arthritis or Crohn’s disease