Content Information
Disease Information
Overview
Also known as: TB, Consumption
- Health Agency (LPHA): Follow-up required
Iowa Department of Public Health TB Control Program: (515) 281-8636 or
(515) 281-7504
Secure Fax: (515) 281-4570
A. Agent
TB is a communicable disease caused by Mycobacterium tuberculosis, sometimes referred to as the tubercle bacillus. It is spread primarily by tiny airborne particles (droplet nuclei) expelled from a person who has infectious TB. If another person inhales air containing these droplet nuclei, transmission may occur. Some bacilli reach the alveoli, where they are ingested by macrophages. Infection begins with the multiplication of tubercle bacilli within these alveolar macrophages. Some of the bacilli spread through the bloodstream when the macrophages die; however, the immune system response usually contains the bacilli and prevents the development of disease. Persons who are infected but who do not have TB disease are asymptomatic and not infectious; such persons usually have a positive reaction to the tuberculin skin test (PPD). Only 10% of infected persons will develop TB disease at some time in their lives, but the risk is considerably higher for persons who are immunosuppressed, especially those with HIV infection. Although the majority of TB disease in adults is pulmonary, TB can occur in almost any anatomical site or as disseminated disease.
B. Clinical Description
Symptoms: The general symptoms of TB disease include feeling sick or weak, weight loss, fever, and night sweats. The symptoms of pulmonary TB include coughing, chest pain, and coughing up blood. Other symptoms depend on the part of the body that is affected.
Onset: Persons at the highest risk of becoming infected with tuberculosis are close contacts — persons who have had prolonged, frequent, or intense contact with a person with infectious TB. Close contacts may be family members, roommates, friends, co-workers, or others. Data collected by CDC since 1987 show that infection rates have been relatively stable, ranging from 30% for the contacts of infectious TB patients.
Complications: Person’s with TB can develop life-threatening complications. Worldwide, approximately two million people die each year from TB. If treated properly and early enough, people with TB can be cured.
Infants/children -- LTBI: Because of their age, infants and young children with LTBI are known to have been infected recently, and thus are at a high risk of their infection progressing to disease. Infants and young children are also more likely than older children and adults to develop life-threatening forms of TB. Children <5 years of age who are close contacts should receive treatment for LTBI even if the tuberculin skin test result and chest radiograph do not suggest TB, because infected infants may be anergic as late as 6 months of age. A second tuberculin test should be done 8 – 10 weeks after the last exposure to infectious TB. Treatment of LTBI can be discontinued if all of the following conditions are met:
- The infant is at least 6 months of age;
- The second tuberculin skin test is negative;
- The second test was performed at least 8 weeks after the child was last exposed to infectious TB.
- Infants/children –TB disease: Because of the high risk of disseminated tuberculosis in infants and children younger than 5 years of age, treatment should be started as soon as the diagnosis of tuberculosis is suspected.
C. Reservoirs
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Common reservoirs: Humans
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Less Common reservoirs: Livestock, wildlife, mainly for m. bovis.
D. Modes of Transmission
Spread: TB germs are placed in the air when a person with pulmonary TB disease of the lungs or throat coughs, sneezes, speaks or sings. When a person inhales air that contains TB germs, he or she may become infected. Pulmonary Tuberculosis (TB) is spread from person to person through the air. It usually affects the lungs, but it can also affect other parts of the body, such as the brain, kidneys, or spine. People with TB infection (and not disease) do not feel sick and do not have any symptoms. However, they may develop TB disease at some time in the future.
People with TB disease are most likely to spread it to people they spend time with every day, such as family members or co-workers. If someone thinks they have been around someone who has TB disease, they should go to their medical provider or the local health department for tests. It is important to remember that people who have TB infection but not TB disease cannot spread the germs to others.
E. Incubation period
For people with latent TB infection (LTBI) and no risk factors, the risk of LTBI developing into disease is about 10% over a lifetime. For people with TB infection and diabetes, the risk is 3 times higher, or about 30% over a lifetime. For people with TB infection and HIV infection, the risk is about 7% to 10% PER YEAR, a very high risk over a lifetime.
F. Period of Communicability or Infectious Period
In general, patients who have suspected or confirmed active TB should be considered infectious if
- (a) they are coughing, undergoing cough-inducing procedures, or their sputum smears are positive for acid-fast bacilli; and
- (b) they are not receiving therapy, have just started therapy, or have a poor clinical or bacteriologic response to therapy.
The infectious period is closed when the following criteria are satisfied:
- effective treatment (as demonstrated by M. tuberculosis susceptibility results) for >2 weeks;
- diminished symptoms; and
- mycobacteriologic response (e.g., decrease in grade of sputum smear positivity detected on sputum-smear microscopy).
The exposure period for individual contacts is determined by how much time they spent with the index patient during the infectious period. Multidrug-resistant TB (MDR TB) can extend infectiousness if the treatment regimen is ineffective. Any index patient with signs of extended infectiousness should be continually reassessed for recent contacts.
More stringent criteria should be applied for setting the end of the infectious period if particularly susceptible contacts are involved. A patient returning to a congregate living setting or to any setting in which susceptible persons might be exposed should have at least three consecutive negative sputum AFB smear results from sputum collected >8 hours apart (with one specimen collected during the early morning) before being considered noninfectious.
G. Epidemiology
One third of the world’s population is infected with the TB bacteria and each year over 9 million people around the world become ill from it. An estimated 10 - 15 million persons in this country are infected with M. tuberculosis. TB disease may develop in these persons at some time in the future. For current TB data, please refer to the IDPH TB Control webpage: www.idph.state.ia.us/ImmTB/TB.aspx?prog=Tb&pg=TbHome
H. Bioterrorism Potential
None.
I. Additional Information
The Council of State and Territorial Epidemiologists (CSTE) surveillance case definitions for Tuberculosis can be found at: www.cdc.gov/osels/ph_surveillance/nndss/phs/infdis.htm#top
CSTE case definitions should not affect the investigation or reporting of a case that fulfills the criteria in this chapter. (CSTE case definitions are used by the state health department and the CDC to maintain uniform standards for national reporting.)
In the United States, the vast majority of TB cases are caused by Mycobacterium tuberculosis, sometimes referred to as the tubercle bacillus. M. tuberculosis and six very closely related mycobacterial species (M. bovis, M. africanum, and M. microti, M. canetii, M. caprae, M. pinnipeddi) can cause tuberculosis disease, and they compose what is known as the M. tuberculosis complex. Mycobacteria other than those comprising the M. tuberculosis complex are called nontuberculous mycobacteria. Nontuberculous mycobacteria may cause pulmonary disease resembling TB.
Fact Sheets and Forms
References
Centers For Disease Control and Prevention – Division of Tuberculosis Elimination www.cdc.gov/tb/
Heymann, D.L., ed. Control of Communicable Diseases Manual, 20th Edition. Washington, DC, American Public Health Association, 2015.
Additional Resources
Treatment of Tuberculosis: MMWR June 20, 2003 / 52(RR11); 1-77 www.cdc.gov/mmwr/preview/mmwrhtml/rr5211a1.htm
Iowa Department of Public Health Tuberculosis website: www.idph.state.ia.us/ImmTB/TB.aspx?prog=Tb&pg=TbHome