There are generally two stages of TB infection, one where the bacteria can be spread and can cause illness and one where the bacteria is in a person’s body, but is not causing disease and cannot be spread.
People with TB infection have TB bacteria in their bodies but they are not sick because the bacteria are not active. These people do not have symptoms of TB disease and they cannot spread the bacteria to others. However, they may develop TB disease in the future. They are often prescribed treatment to prevent them from developing TB disease.
People with TB disease are sick from TB bacteria that are active, meaning that they are multiplying and destroying tissue in their body. They usually have symptoms of TB disease. People with TB disease of the lungs or throat are capable of spreading their illness to others. They are prescribed drugs that can treat TB disease.
Tuberculosis infection may result after close contact with a person who has tuberculosis disease. Tuberculosis infection is determined by a significant reaction to the Mantoux skin test with no symptoms of tuberculosis, and no TB bacteria found in the sputum. Tuberculosis disease is characterized by the appearance of symptoms, a significant reaction to a Mantoux skin test and identification of TB bacteria.
To spread the TB bacteria, a person must have TB disease. Having TB infection is not enough to spread the bacteria. Tuberculosis may last for a lifetime as an infection, never developing into disease. However, individuals with TB infection are at considerable risk of developing TB disease, particularly during the first year after acquiring the infection. Additionally, individuals with weakened immune systems such as persons infected with HIV are at high risk of developing TB disease if TB infection is untreated.