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Self-Study Modules on Tuberculosis

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Module 6: Contact Investigations for Tuberculosis
Summary

A contact investigation is a procedure for

  • Identifying people who were exposed to someone with infectious TB disease
  • Evaluating these people for latent TB infection (LTBI) and TB disease
  • Providing appropriate treatment for those with LTBI and TB disease

A contact investigation is important to find contacts who

  • Have TB disease so that they can be given treatment, and further transmission can be stopped
  • Have LTBI so that they can be given treatment for LTBI
  • Are at high risk of developing TB disease and may need treatment for LTBI until it becomes clear whether they have TB infection

A person with suspected or confirmed TB disease who is the initial case reported to the health department is called the index patient. A contact investigation should be done whenever a person is found to have or is suspected of having infectious TB disease, and it should be started as soon as TB is diagnosed or strongly suspected in a patient. The health department is legally responsible for ensuring that a complete contact investigation is done for the TB cases reported in its area. For a contact investigation to be successful, infected contacts should begin and complete a regimen of treatment for LTBI. A successful contact investigation can interrupt transmission and prevent future cases of disease.

A contact investigation should be done when TB is confirmed or there is a high clinical suspicion of TB. While AFB sputum smear-negative TB disease usually indicates a lower bacterial burden than AFB smear-positive disease, and thus a lower risk of transmission, contact investigations for negative-smear cases usually should be conducted.

There are some instances in which contact investigations are not performed. For example, extrapulmonary TB (without pulmonary TB) does not carry any risk for transmission and contact investigations are not performed. Likewise, contact investigations are not performed for people with diseases caused by nontuberculous mycobacteria only, such as M. avium complex. In addition, young children with TB disease are rarely infectious, so a contact investigation is generally not conducted when a child is found to have TB disease.

In some situations, a source case investigation is conducted to find the source of TB transmission when recent transmission is likely. This is usually done when

  • A young child is found to have TB infection or disease
  • A severely immunosuppressed person who does not have a known history of TB infection is found to have TB disease
  • A cluster of tuberculin skin test conversions is found in a high-risk institution (for example, health care or correctional facility)

In general, there are three different types of places where patients may spend most of their time.

  • Household or residence
  • Work or school
  • Leisure or recreational environments

A contact investigation involves these steps:

  1. Medical record review. The first step in a contact investigation is to review the TB patient's medical record and ask the clinician for information to determine whether the patient has been infectious and, if so, when. Knowing about the patient's infectiousness helps health care workers decide which contacts are at risk. The health care worker collects information about the site of TB disease, the patient's TB symptoms, sputum smear and culture results, results of nucleic acid amplification testing (if available), chest x-ray results, TB treatment, and method of TB administration. In addition, the period of infectiousness should be determined. The period of infectiousness is the time period during which a person with TB disease is capable of transmitting M. tuberculosis. Determining the period of infectiousness can help focus the contact investigation efforts on those persons who were exposed while the patient was infectious. There is no universal, well-established method to determine the period of infectiousness. The beginning of the infectious period is usually estimated by determining the date of onset of the patient's symptoms (especially coughing).

  2. Patient interview. The next step in the contact investigation is to interview the TB patient. The patient interview is one of the most critical parts of the contact investigation, because the health care worker who interviews the patient serves as the main link between the health department and the contacts. If the health care worker does not communicate well enough with the patient to get accurate information about symptoms, places, and contacts, people who need evaluation and treatment may be missed.

  3. Field investigation. The next step is to conduct a field investigation. This means visiting the patient's home or shelter, workplace (if any), and the other places where the patient said he or she spent time while possibly infectious. The field investigation is important and should be done even if the patient interview has already been conducted. The purpose of the field investigation is to identify contacts and evaluate the environmental characteristics of the place in which exposure occurred. The field investigation may provide additional information for the risk assessment and identify additional contacts.

    The health care worker visits the places where the patient spent time in order to observe environmental characteristics; identify additional contacts; look for evidence of other contacts; interview and skin test contacts who are present; educate contacts about the purpose of contact investigation, the basics of transmission, the risk of transmitting tuberculosis, and the importance of testing, treatment, and follow-up for TB infection and disease; and refer contacts who have TB symptoms to the health department for a medical evaluation including sputum collection.

  4. Risk assessment for TB transmission. Using information about the patient's period of infectiousness, the environmental characteristics of the places where the patient spent time, and the characteristics of the contacts' exposure, the health care worker assesses the risk of TB transmission. Contacts who spent time with the patient during the period of infectiousness are at higher risk for exposure and infection, especially if they had close, prolonged exposure in a small or crowded, poorly ventilated area. Also contacts exposed to patients with a high degree of infectiousness are at risk for TB transmission.

  5. Decision about priority of contacts. To use time and resources wisely, the contact investigation should be focused on the high-priority contacts, the contacts who are most at risk for developing TB infection or TB disease. In other words, the highest priority for testing should be given to
  • Contacts who are most likely to be infected, based on the risk that M. tuberculosis was transmitted
  • Contacts who are at high risk of developing disease if infected, including young children less than 4 years of age, HIV-infected and other immunosuppressed persons, and persons with certain medical conditions Contacts with less intense or less frequent exposure are classified as other-than-close contacts, and they should be given a lower priority.

  1. Evaluation of contacts. Contacts should be evaluated for LTBI and TB disease. This evaluation includes at least a medical history and a Mantoux tuberculin skin test (unless there is a previous documented positive reaction). For immunosuppressed contacts or contacts under 4 years of age, the evaluation should also include a chest x-ray. Any contact who has TB symptoms should be given both a chest x-ray and sputum examination. Contacts with a negative initial skin test reaction to a skin test given less than 10 to 12 weeks postexposure should be retested after the window period.

  1. Treatment and follow-up for contacts. The following contacts should be evaluated for treatment for LTBI:

    Contacts who have a positive tuberculin skin test reaction and no evidence of TB disease

    • High-risk contacts who have a negative tuberculin skin test reaction, such as children under 4 years of age, HIV-infected people, and other high-risk contacts who may develop TB disease very quickly after infection

    • High-risk contacts (including children under 4 years of age) with a negative skin test reaction less than 10 to 12 weeks after their exposure should start treatment for LTBI and be retested after the window period ends. This is called window period prophylaxis. If the second skin test reaction is negative, treatment for LTBI is usually stopped. If the second skin test reaction is positive, they should continue taking treatment for LTBI. Contacts who have a positive sputum smear or chest x-ray results suggestive of current TB disease should begin treatment for TB disease. The adherence of all patients receiving TB treatment for LTBI or treatment for TB disease should be monitored closely.

  2. Decision about whether to expand testing. Contacts should be tested in the order of their exposure time and risk, starting with the highest-priority group. This method is called the concentric circle approach. Evidence of recent TB transmission among the high-priority contacts, such as a high infection rate (percentage of contacts with a similar amount of exposure who have a newly identified positive skin test reaction), TB infection in a young child, a documented contact skin test conversion, or a secondary case of TB, determines whether the next group of contacts should be screened. Decisions about expanding contact investigations to the next group of contacts should be made by clinical and supervisory staff based on an assessment of all available information. If there is NO evidence of recent TB transmission, then testing should NOT be expanded to the next group of contacts. If there IS evidence of recent transmission, the next highest priority group should be evaluated. The investigation should expand to the next group each time there is evidence of transmission in the group being tested. The particular circumstances of each case need to be carefully considered in order to expand testing to include all those likely to be at risk.

  3. Evaluation of contact investigation activities. To complete the investigation, an evaluation should be conducted with or by a supervisor to determine such things as
    • Were an appropriate number of contacts identified?
    • Were the highest-priority contacts located and tested?
    • Was the contact investigation performed in all settings: household or residence, work or school, and leisure or recreational environments?
    • Was the contact investigation expanded appropriately?
    • Were contacts completely evaluated (including second skin test if needed) and given appropriate therapy if they had TB infection or disease?
    • How many infected contacts completed a regimen of treatment for LTBI?
    • Did all identified cases complete an adequate treatment regimen?

Additional Reading

American Thoracic Society/Centers for Disease Control. Diagnostic standards and classification of tuberculosis. Am Rev Respir Dis. 1990;142:725-735.

American Thoracic Society/Centers for Disease Control. Control of tuberculosis in the United States. Am Rev Respir Dis. 1992;146:1623-1633.

Centers for Disease Control and Prevention. Tuberculosis control laws -- United States, 1993: recommendations of the Advisory Council for the Elimination of Tuberculosis (ACET). MMWR. 1993;42(RR-15):1-28.

Centers for Disease Control and Prevention. Screening for tuberculosis and tuberculosis infection in high-risk populations: recommendations of the Advisory Council for the Elimination of Tuberculosis (ACET). MMWR. 1995;44(RR-11):1-17.

Daley CL, Small PM, Schecter GF, et al. An outbreak of tuberculosis with accelerated progression among persons infected with the human immunodeficiency virus. N Engl J Med. 1992;326:231-235.

Etkind SC. Contact tracing in tuberculosis. In: Reichman L, Hershfield E, (eds): Tuberculosis: A Comprehensive International Approach. New York: Marcel Dekkar; 1993, pp 275-289.

Effective Tuberculosis Interviews: A Course on Interviewing and Communications Skills. This is a 3-day, interactive course designed to be taught by supervisory TB staff or other staff in state and local health departments. The purpose of the course is to improve interviewing and communications skills among new health department staff assigned to interview TB patients and suspects, conduct field investigations, foster patients' adherence to treatment, and assist with directly observed therapy. For more information on the availability of this course in your area, please ask your local TB program manager.

How to be"Streetwise"-- and Safe. National Crime Prevention Council and Federal Protective Service. Brochure NCPB-002. (Can be ordered by calling 1-800-548-0325.)

Leonhardt KK, Gentile F, Gilbert BP, Aiken M. A cluster of tuberculosis cases among crack house contacts in San Mateo County, California. Am J Pub Health. 1994;84(11):1834-1836.

Lewis ID, Hallburg JC. Strategies for Safe Home Visits. Urban Health. 1980;9(6):40-41.

 
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