Clinically significant disease occurs through progression of primary infection or through later reactivation of latent TB infection (LTBI); this is most likely to occur in the first few years following infection, although late reactivation can occur several decades later, particularly in individuals who become immunosuppressed. Risk of TB acquisition is increased in people who have come to the UK from high incidence countries or who are born in the UK but come from high-risk ethnic minority groups. Other risk groups include those who are homeless, in prison or who misuse drugs or alcohol.