The rate of tuberculosis infection in the United States had been declining steadily until 1984 and then increased. Numerous factors account for the resurgence of tuberculosis in the United States and in Europe. The rapid response of state and federal agencies in the United States has averted a potentially drastic rise in incidence. It also provides the organism with a resistant barrier to many common drugs. The organism is difficult to study in the laboratory.
Slow growth makes culturing a lengthy process and colony formation can take several weeks.
TB bacilli form clumps, making them difficult to work with and count. Because it is a dangerous airborne pathogen, study requires special safety equipment. The bacteria's primary host is the human. When an infected person talks, coughs, sings, or spits, tiny aerosolized droplets containing bacteria are released into the air and inhaled by uninfected persons. Viable bacteria can remain in the air for a long time.