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TB Elimination

The Difference Between Latent TB 

Infection and TB Disease

National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention 

Division of Tuberculosis Elimination

What is TB?

Tuberculosis (TB) is a disease caused by a 

germ called Mycobacterium tuberculosis that 

is spread from person to person through the 

air. TB usually affects the lungs, but it can also 

affect other parts of the body, such as the brain, 

the kidneys, or the spine. When a person with 

infectious TB coughs or sneezes, droplet nuclei 

containing M. tuberculosis are expelled into 

the air. If another person inhales air containing 

these droplet nuclei, he or she may become 

infected. However, not everyone infected with 

TB bacteria becomes sick. As a result, two TBrelated conditions exist: latent TB infection and 

TB disease.

What is Latent TB Infection?

Persons with latent TB infection do not feel 

sick and do not have any symptoms. They are 

infected with M. tuberculosis, but do not have 

TB disease. The only sign of TB infection is a 

positive reaction to the tuberculin skin test or 

TB blood test. Persons with latent TB infection 

are not infectious and cannot spread TB 

infection to others.

Overall, without treatment, about 5 to 10% 

of infected persons will develop TB disease at 

some time in their lives. About half of those 

people who develop TB disease will do so within 

the first two years of infection. For persons 

whose immune systems are weak, especially 

those with HIV infection, the risk of developing 

TB disease is considerably higher than for 

persons with normal immune systems.

Of special concern are persons infected by 

someone with extensively drug-resistant TB 

(XDR TB) who later develop TB disease; these 

persons will have XDR TB, not regular TB disease.

A person with latent TB infection

• Usually has a skin test or blood test result 

indicating TB infection 

• Has a normal chest x-ray and a negative 

sputum test 

• Has TB bacteria in his/her body that are alive, 

but inactive 

• Does not feel sick 

• Cannot spread TB bacteria to others

• Needs treatment for latent TB infection to 

prevent TB disease; however, if exposed and 

infected by a person with multidrug-resistant 

TB (MDR TB) or extensively drug-resistant TB 

(XDR TB), preventive treatment may not be an 

option 

What is TB Disease?

In some people, TB bacteria overcome the defenses 

of the immune system and begin to multiply, 

resulting in the progression from latent TB infection 

to TB disease. Some people develop TB disease 

soon after infection, while others develop TB 

disease later when their immune system becomes 

weak.

The general symptoms of TB disease include

• Unexplained weight loss 

• Loss of appetite 

• Night sweats 

• Fever 

• Fatigue 

• Chills 
The symptoms of TB of the lungs include

• Coughing for 3 weeks or longer 

• Hemoptysis (coughing up blood) 

• Chest pain 

Other symptoms depend on the part of the body 

that is affected.

Persons with TB disease are considered 

infectious and may spread TB bacteria to 

others. If TB disease is suspected, persons should 

be referred for a complete medical evaluation. 

If it is determined that a person has TB disease, 

therapy is given to treat it. TB disease is a serious 

condition and can lead to death if not treated.

A person with TB disease

• Usually has a skin test or blood test result 

indicating TB infection 

• May have an abnormal chest x-ray, or 

positive sputum smear or culture 

• Has active TB bacteria in his/her body 

• Usually feels sick and may have symptoms 

such as coughing, fever, and weight loss 

• May spread TB bacteria to others 

• Needs treatment to treat TB disease 

Additional Information

1. American Thoracic Society (ATS) and CDC. 

Diagnostic standards and classification 

of tuberculosis in adults and children. 

(PDF) Am J Respir Crit Care Med 2000; 161. 

http://ajrccm.atsjournals.org/cgi/content/

full/161/4/1376

2. CDC. Questions and Answers About TB. 

http://www.cdc.gov/tb/publications/faqs/

default.htm

3. CDC. Multidrug-Resistant Tuberculosis (MDR 

TB). http://www.cdc.gov/tb/publications/

factsheets/drtb/mdrtb.htm

4. CDC. Extensively Drug-Resistant 

Tuberculosis (XDR TB). http://www.cdc.gov/

tb/publications/factsheets/drtb/xdrtb.htm

http://www.cdc.gov/tb

November 2011