Tuberculosis (TB) incidence, described by the World Health Organization as the number of new cases arising within a given time period, was estimated to be at 4.2 per 100,000 in 2008. In other words, 4.2 out of 100,000 people in the United States were diagnosed with TB in 2008, for a total of 12,904.
There are two types of tuberculosis, one of which results in illness. Individuals infected with active tuberculosis are symptomatic and contagious. Symptoms include unexplained weight loss, loss of appetite, coughing for three weeks or longer, coughing up blood and chest pain. The second type is latent tuberculosis. Individuals infected with this type have no symptoms and are not contagious because they are not actually sick, although they are very susceptible to becoming sick. Only those with active tuberculosis are counted as cases.
Factors that affect the incidence of both types of tuberculosis are similar. The main factors, poverty and education level, are very broad and thus, they have been broken down into the more specific factors.
Close/Sustained Contact with a Person with Infectious TB
The majority of people who get TB (latent and active) get it from people they are around frequently, such as a family member or co-worker. If you suspect a family member or co-worker has active TB, suggest that they seek treatment. Until they are cured, wear a mask when around them or ask them to wear a mask.
Contact with Persons who Have Immigrated from High-TB Areas
The World Health Organization keeps track of reported tuberculosis incidence. In 2007, the regions with the highest numbers of tuberculosis cases were sub-Saharan Africa, southeast Asia and the eastern Mediterranean. Contact with individuals from these regions increases one's risk for getting TB. According to the Centers for Disease Control and Prevention (CDC), nearly 60 percent of reported TB cases in the United States in 2008 were in foreign-born individuals.
Homelessness
The CDC reports that in 2003, 6.3 percent of reported TB cases in the United States were in homeless persons. There is an increased risk for TB infection in this population because of its lack of adherence to TB treatment, which can take up to eight months, and because of the close quarters homeless persons endure when sleeping in homeless shelters.
Injection Drug Use
Injection drug users have a higher risk of contracting TB because of their lowered immune function, proximity to other drug users who may already have active TB and low adherence to treatment.
HIV Infection
Co-infection with HIV and TB is very common. People with latent TB who are also infected with HIV are much more likely to convert to active TB, according to the CDC.
Persons Who Work or Reside with People at High Risk for TB
Facilities, such as hospitals, homeless shelters, correctional facilities, nursing homes and residential homes, for those with HIV are high-risk environments for employees and those staying there. Because these types of facilities are more likely to house contagious TB patients, the likelihood is great that a latent infection could become active because of prolonged exposure to the disease.
Persons with Medical Conditions That Weaken the Immune System
People with HIV infection or who use injection drugs are at higher risk for TB because both of those situations weaken the immune system. Other groups with reduced immune function include people with silicosis, diabetes mellitus, severe kidney disease, and head and neck cancers. People who have had organ transplants or are undergoing treatment with corticosteroids or treatment for rheumatoid arthritis or Crohn's disease are at higher risk as well.
References
- Morbidity and Mortality Weekly Report; Tuberculosis Transmission in a Homeless Shelter Population; J. Hudson, et.al.; Feb. 18, 2005
- American Journal of Respiratory and Critical Care Medicine; Tuberculosis Incidence in U.S.-Born and Foreign-Born Persons; D.P. Chin, et.al.; December 1998
- World Health Organization: Tuberculosis Fact Sheet
