Latent TB Infection (TB Infection)
2018 Case Definition

Background

TB is a disease caused by a bacterium called Mycobacterium tuberculosis (MTB). The active form of tuberculosis (TB Disease) was once the leading cause of death in the United States (US). TB Disease is spread through the air from one person to another when the disease is located in the lungs. People nearby may breathe in these bacteria and become infected.

Not everyone infected with M. tuberculosis becomes sick. People who are not sick have what is commonly called Latent TB Infection (TB Infection). People with TB Infection do not feel sick, do not have any symptoms, and cannot spread TB to others. Nevertheless, some people with TB Infection go on to develop TB Disease in the course of their lifetimes. Likelihood of developing TB Disease is variable depending on a number of risk factors.

Clinical Criteria

Clinical criteria alone are not sufficient to classify a case of TB Infection.Clinical criteria to confirm a suspected case of TB Infection are as follows:

No clinical evidence compatible with TB Disease including:

No signs or symptoms consistent with TB Disease

AND

1)Chest imaging without abnormalities consistent with TB (chest radiograph or CT scan)

OR

• 2)Abnormal chest imaging that could be consistent with TB Disease with microbiologic testing that is negative for MTB complex

AND

where TB Disease has been clinically ruled out

Laboratory Criteria For Diagnosis

Laboratory/diagnostic criteria alone are not sufficient to confirm a case of TB Infection. Laboratory criteria to identify suspected cases of TB Infection are as follows:

A positive tuberculin skin test (TST) [As defined by the CDC (see reference)]

OR

A positive interferon gamma release assay (IGRA) [As defined by the CDC (see reference)]

Criteria to Distinguish a New Case from an Existing Case

A new case is an incident TB Infection case that meets the suspected or confirmed case criteria and has not previously been diagnosed or treated for TB Infection OR previously treated for TB Disease.

Suspected

A case that meets one or more of the laboratory criteria

AND

M. tuberculosis complex was not isolated from a clinical specimen, if a specimen was collected

Confirmed

A case that meets one of the laboratory criteria for TB infection

AND

M. tuberculosis complex was not isolated from a clinical specimen, if a specimen was collected

AND

Meets the clinical criteria for TB Infection as listed above