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Module 6: Contact Investigations for Tuberculosis
Background

Contact investigations are a very good way to find people with TB infection and TB disease. In a contact investigation, people who were exposed to someone who has infectious TB disease (contacts) are identified and evaluated for TB infection and TB disease. Contacts are at high risk for infection with M. tuberculosis. If recently infected, contacts are also at high risk for developing TB disease. Therefore, it is important to identify and evaluate contacts so that they can be given treatment for disease if they have TB or given treatment for latent TB infection (LTBI) as appropriate to reduce their risk of developing TB disease.

In this module, you will learn about the goals of a contact investigation and the steps required to conduct one. A successful contact investigation includes these steps: a medical record review, an interview with the index patient, and a field investigation. When transmission may have occurred, these steps are followed by a risk assessment for M. tuberculosis transmission, decision making about the relative priority of contacts, and the testing of high-priority contacts (those with the greatest exposure or greatest risk of developing disease if infected). If any contacts have TB infection or TB disease, appropriate treatment and follow-up care are provided. The concentric circle approach can be used to decide whether to expand the testing to contacts who had less exposure to the index case. Finally, an evaluation of contact investigation activities should be conducted.

Objectives

After working through this module, you will be able to:
  1. Define and explain the goals of a contact investigation.
  2. Describe the situations in which a contact investigation should be done.
  3. Describe how to prioritize a contact investigation.
  4. Describe the steps in a contact investigation.
  5. List the information that should be collected during the medical record review.
  6. Describe the purposes of the interview with the index patient.
  7. Describe the purposes of the field investigation.
  8. List the factors that affect the risk of M. tuberculosis transmission.
  9. Describe which contacts should be considered high-priority contacts.
  10. Describe how contacts should be evaluated for TB infection and TB disease.
  11. Describe the procedures for treatment and follow-up of contacts with TB infection or TB disease.
  12. Describe the decision-making process about whether to expand testing.
  13. Describe the concentric circle approach.
  14. Describe why it is important to evaluate contact investigations.

New Terms

Lists of new terms were introduced in each of the five core Self-Study Modules on Tuberculosis (Modules 1-5). Please refer to the core modules or their Glossary if you encounter unfamiliar terms related to TB that are not defined in this New Terms section.

Look for the following new terms in this module.

close contact - a person who had prolonged, frequent, or intense contact with a person with TB while he or she was infectious. Close contacts are more likely to become infected with M. tuberculosis than contacts who see the patient less often

concentric circle approach - a method of testing contacts in order of their exposure time (close vs. other-than-close) and their risk (high priority vs. low priority) with close contacts and other contacts at high risk of developing TB disease tested first; it includes contacts from environments where contact may have taken place (household or residential, work or school, and leisure or recreation environments)

contact investigation - a procedure for identifying people exposed to someone with infectious TB, evaluating them for latent TB infection (LTBI) and TB disease, and providing appropriate treatment for LTBI or TB disease (see contacts)

contacts - people exposed to someone with infectious TB disease, generally including family members, roommates or housemates, close friends, coworkers, classmates, and others (see close contacts or other-than-close contacts)

exposure to TB - time spent with or near someone who has infectious TB disease

field investigation - visiting the patient's home or shelter, workplace (if any), and the other places where the patient said he or she spent time while infectious. The purpose of the field investigation is to identify contacts and evaluate the environmental characteristics of the place in which exposure occurred

high-priority contacts - the contacts who are at most risk for TB infection or disease; contacts who are most likely to be infected and high-risk contacts (see high-risk contacts)

high-risk contacts - the contacts (either close or other-than-close) who are at a particularly high risk of developing TB disease if they become infected with M. tuberculosis (e.g., young children less than 4 years of age, HIV-infected and other immunosuppressed persons, and persons with certain medical conditions)

index patient - a person with suspected or confirmed TB disease who is the initial case reported to the health department. The index case may or may not be the source case (see source patient)

infection rate - the percentage of contacts with a similar amount of exposure (e.g., close, other-than-close) who have a newly identified positive skin test reaction (5 or more millimeters of induration)

latent TB infection (LTBI) - also referred to as TB infection. Persons with latent TB infection carry the organism that causes TB but do not have TB disease, are asymptomatic, and are noninfectious. Such persons usually have a positive reaction to the tuberculin skin test

local community - the geographic area where a person lives and spends time; may be a residential area or an ethnic community (i.e., groups of people who emigrated from the same geographic area)

other-than-close contacts - contacts with less intense, less frequent, or shorter durations of contact to the TB patient than close contacts (see close contact)

open-ended questions - questions that cannot be answered with a simple "yes" or "no." They are designed to elicit the patient's knowledge, feelings, and beliefs by beginning with words such as "What," "Why," "Who," "How," and "When," that demand an explanation; they are used to explore complex issues that do not have a finite or predetermined set of responses

period of infectiousness - time period during which a person with TB disease is capable of transmitting M. tuberculosis; usually estimated by determining the date of onset of the patient's symptoms (especially coughing)

secondary case - a contact who has developed TB disease as a result of transmission from an index patient

skin test conversion for contacts - defined differently from a standard skin test conversion; for contacts, a skin test conversion is defined as a change from less than 5 mm on the initial skin test to a reaction of greater than or equal to 5 mm on the second test, 10 to 12 weeks after exposure

source case investigation - conducted to find the source of transmission when recent transmission is likely; used to determine who transmitted M. tuberculosis to an index patient or infected child or persons in the cluster of skin test conversions, whether this person is still infectious, whether the case of TB in this person was reported to the health department, and whether others were infected by the source patient (see source patient)

source patient - a person with infectious TB disease who is responsible for transmitting M. tuberculosis to another person or persons. He or she is identified through either a contact or source case investigation and may or may not be the index patient (see index patient)

window period - the time span between the date of an initial tuberculin skin test with a negative reaction and the date of the follow-up tuberculin skin test that should take place 10 to 12 weeks after exposure; after the window period has ended, a repeat skin test should be administered to each contact who had an initial negative reaction

window period prophylaxis - the practice of providing treatment for latent TB infection to high-risk contacts (including young children under 4 years of age, and HIV-infected and other immunosuppressed persons) with an initial negative skin test reaction less than 10 to 12 weeks after their exposure; if the contact has a negative skin test reaction after the window period, treatment for latent TB infection is usually stopped (see window period)

 
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