TB infection occurs when TB germs are breathed in and establish infection initially in the lungs. In most healthy individuals the immune system is able to keep the infection in check. This is referred to as latent TB infection. TB occurs when conditions tip in favour of the TB germs because the immune system is weakened due to HIV infection, malnutrition, silicosis, cancer therapy or other chronic diseases such as diabetes, long-term steroid therapy, alcoholism, and physical and emotional stress. The TB bacteria then start replicating, causing increasing inflammation and tissue destruction until the person shows the signs and symptoms of TB.