Self-Study Modules on Tuberculosis
Module 6: Contact Investigations for Tuberculosis
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 (Table 6.6).
Contacts Most Likely to be Infected
These are people who had close, regular, prolonged contact with the TB patient while he or she was infectious, especially in small, poorly ventilated places. These contacts are classified as close contacts, and usually include people who have shared a house or room with the patient or spent time with the patient frequently during the period of infectiousness. Contacts with less intense, less frequent, or shorter durations of contact to the TB patient are classified as other-than-close contacts, and they generally should be given a lower priority for testing.
It is not always possible to easily classify contacts as "close" or "other-than-close" right away because the health care worker may continue to receive information as the contact investigation continues. Contacts who are considered to have the most exposure to the patient should receive highest priority and contacts who have the least exposure should be given the lowest priority based on available information. The priority given to a contact can change over time as new information is collected and old information is updated and revised. Decisions about the prioritization of contact investigations should be made by supervisory and clinical staff. For example
- A family member who lives in the same home or apartment as the patient is a close contact; a family member or friend who lives elsewhere but visits for a few hours every other week is an other-than-close contact
- Likewise, the coworker of an infectious TB patient who works alongside the patient each day for several hours in a small restaurant kitchen is a close contact; a delivery person who brings produce to the restaurant 2 days a week and is exposed to the patient for 15 minutes each time is an other-than-close contact
- A person who drinks with the patient at the local bar for a few hours three times a week is a close contact; a person who plays pool with the patient two times each month is an other-than-close contact
A very low priority contact would be someone who met the patient once or twice briefly during the period of infectiousness. If there is evidence that close contacts have been infected, then other-than-close contacts may be tested.
By using the factors included in Table 6.6 to assess a contact's risk of becoming infected, it should be possible to define a group of close contacts: those persons who are most likely to have been infected.
Contacts at High Risk of Developing TB Disease if Infected
Some conditions, such as HIV infection, immunosuppressive therapy, and low body weight, increase the risk that TB infection will progress to TB disease (see Module 1, Transmission and Pathogenesis of Tuberculosis). Contacts with these conditions should be given high priority for TB testing, regardless of whether they are close contacts or other-than-close contacts. Young children less than 4 years of age should also be given high priority for testing, because they can develop serious forms of TB disease very quickly after infection.
High-Priority Contacts for Testing
Most Likely to Be Infected
|Contacts at High Risk of Developing TB Disease Once Infected|
||Contacts who are young children less
than 4 years of age
|Study Questions 6.26-6.28
6.26. Which contacts should be classified as close contacts and are most likely to be infected?
6.27. Which contacts are at high risk of developing TB disease if infected?
6.28. Which contacts should be considered high-priority contacts for testing?
|Case Study 6.6
You are in charge of the contact investigation for 35-year-old Hector Gonzalez, who is strongly suspected of having pulmonary TB disease. One week ago, Hector came to the health department complaining of night sweats, a 10-pound weight loss, and a persistent cough that has lasted about a month. His sputum smears were positive for AFB, and he started four-drug treatment for TB disease.
When you interviewed Hector 3 days ago, you found out that he lives with his 32-year-old wife, Mimi; two sons, Luis, 2, and Javier, 4; and his mother-in-law, Alma, 65. Hector's cousin, Henry, has stopped by the house a few times in the past month. Hector informed you that Henry has been HIV positive for 2 years.
Hector rides to work every day with his friend Joe. The ride lasts about half an hour. Hector works in a car assembly plant. About 100 employees work in the main room with Hector, but the room is divided into several sections. There are 20 people in Hector's section, and 4 of these people are assigned to work closely with Hector. Hector eats lunch outside every day with these 4 coworkers.
About twice a week and on weekends, Hector goes to a small neighborhood bar located in the basement of a building. At the bar, Hector spends most of the time talking to the bartender.
What Does the Evaluation Include?
Evaluation of TB contacts should be done in an orderly manner, starting with the highest-priority group 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 who are under 4 years of age, the evaluation should also include a chest x-ray, regardless of skin test result, because of the possibility of a false-negative reaction to the tuberculin skin test and risk of early progression to TB disease if infected (see Module 3, Diagnosis of Tuberculosis Infection and Disease).
In addition, any contact who has TB symptoms should be given both a chest x-ray and a sputum examination.
Contacts should be asked about their
- History of TB infection or disease
- Documented previous tuberculin skin test results
- Previous treatment for TB infection or disease
- Previous exposure to TB
- Risk factors for developing TB disease
- Current symptoms of TB
Contacts should be questioned about risk factors for HIV and offered counseling and testing if their HIV status is not known and they are at risk.
Mantoux Tuberculin Skin Test
All high-priority contacts should be given a Mantoux tuberculin skin test; a reaction of 5 or more millimeters of induration is considered positive for contacts. Some contacts may indicate that they have been vaccinated with BCG. BCG (bacillus Calmette-Gurin) is a vaccine for TB disease that is used in developing countries. However, it is rarely used in the United States because studies have shown that it is not completely effective. People who have been vaccinated with BCG may have a positive reaction to the tuberculin skin test even if they do not have TB infection. This is called a false-positive reaction. There is no reliable way to distinguish a positive tuberculin reaction caused by a vaccination with BCG from a reaction caused by true TB infection. During a contact investigation, people who have a positive reaction to a tuberculin skin test should be further evaluated for TB disease, regardless of whether or not they were vaccinated with BCG (see Module 3, Diagnosis of Tuberculosis Infection and Disease).
Contacts who have a previously documented positive tuberculin skin test should not receive another skin test, but should be evaluated for symptoms of TB disease, and asked about any history of treatment for TB infection or TB disease, and may need a chest x-ray. Depending on the results of the evaluation, some of these contacts may be candidates for treatment for LTBI or TB disease.
Contacts who are skin tested less than 10 to 12 weeks after their last exposure to a patient with infectious TB may have a false-negative reaction, because they may not yet be able to react to the tuberculin. It takes 2 to 12 weeks after TB infection for the body's immune system to react to tuberculin. For this reason, contacts of someone with infectious TB disease who have a negative initial skin test reaction should be retested 10 to 12 weeks after the last contact with the person who has TB disease. The time span between the date of an initial skin test with a negative reaction and the date that is 10 to 12 weeks after exposure is called the window period. After the window period has ended, a repeat skin test should be administered to each contact who had an initial negative reaction.
For example, a contact whose last exposure to TB occurred on July 1 has an initial negative skin test reaction on August 1, only 4 weeks after his or her exposure. This contact should have a repeat test between September 15 and October 1, or 10 to 12 weeks after exposure. The contact's window period is from August 1 through October 1 (Figure 6.7).
As with adults, children should be retested 10 to 12 weeks after exposure. Infants under 6 months of age may have a false-negative skin test reaction because their immune systems are not yet able to react to tuberculin. Infants need careful clinical evaluation.
Figure 6.7 This is a sample time line demonstrating how to determine the window period.
All contacts who have a positive skin test reaction with an induration greater than 5 mm or who report any TB symptoms should be given a chest x-ray. The purpose of the chest x-ray is to rule out the possibility of TB disease and to look for signs of old TB disease before treatment for LTBI is started. The results of a chest x-ray alone cannot confirm that a person has TB disease; smear and culture evaluations are necessary if the chest x-ray results are abnormal.
Certain contacts should have a chest x-ray to evaluate for TB disease at the same time the initial skin test is done, including those who
- Have TB symptoms
- Are HIV-infected or have other immunosuppressed conditions
- Are under 4 years of age
Because of their high risk of quickly developing TB disease, HIV-infected and other immunosuppressed contacts and young children may already have TB disease by the time of the contact investigation.
In addition, if many close contacts have a positive skin test reaction, other high-risk close contacts may be considered for treatment for LTBI even if the initial skin test reaction is negative. This is especially true if the initial skin test was given during the window period or if a false-negative reaction is suspected. Such persons need a chest x-ray to exclude the possibility of TB disease before they begin treatment for LTBI.
Any contact who has an abnormal chest x-ray or who has TB symptoms
should have three sputum specimens collected on different days for
smear and culture examination, regardless of his or her tuberculin
skin test reaction. The results of the smear examination can be
used to help determine the person's infectiousness, although a negative
smear does not rule out the possibility of TB disease (see
Module 3, Diagnosis of
Tuberculosis Infection and Disease).
|Study Questions 6.29-6.32
6.29. For all high-priority contacts, what procedures should be done during evaluation?
6.30. In what situation should tuberculin testing of contacts be repeated?
6.31. Which contacts should be given a chest x-ray?
6.32. What is the purpose of a sputum examination and when should one be done?
|Case Study 6.7
The high-priority contacts you identified in Case Study 6.6 for Hector Gonzalez, a patient suspected of having TB disease, were
These contacts (a total of 11) are being tested by the contact investigation team. Five weeks have passed since the contacts were last exposed to Hector while he was infectious.
None of the contacts had TB symptoms. The skin test results were as follows:
Newly identified positive reaction: Mimi, 32 (11 mm); Javier, 4 (13 mm)
Negative reaction: Luis, 2 (0 mm); Alma, 65 (3 mm); Joe (3 mm); Henry, HIV+ (0 mm); Coworker A (2 mm); Coworker B (0 mm); Coworker C (0 mm); Coworker D (3 mm); the bartender (0 mm)
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
Contacts recently infected with M. tuberculosis are a high-priority group for treatment for LTBI because they are at high risk of developing TB disease. (The highest risk of developing TB disease is in the first 2 years after infection.)
Some contacts who have a negative tuberculin skin test reaction (less than 5 millimeters of induration) should be evaluated for treatment for LTBI, after TB disease has been ruled out. These contacts include children under 4 years of age, HIV-infected and other immunosuppressed people, and others 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. Infants younger than 6 months of age should be evaluated as discussed previously.
HIV-infected contacts or other immunosuppressed contacts may be given a full course of treatment for LTBI, regardless of their skin test results, because of the possibility of a false-negative skin test result. This is particularly true when there is evidence of transmission to other contacts with a similar degree of exposure and likelihood of a false-negative skin test result.
Contacts who have a positive sputum smear or chest x-ray results suggestive of current TB disease should begin treatment for TB disease (see Module 4, Treatment of Tuberculosis Infection and Disease).
Testing, treatment, and follow-up for contacts are summarized in Figures 6.8, 6.9, and 6.10, which present diagrams for
- Contacts 4 years of age or older
- Contacts under 4 years of age
- Immunosuppressed contacts
The following diagrams are presented as guides only, and are not meant to substitute for careful consideration of each contact's risk of exposure, infection, and progression to disease. It is important to always keep in mind the ultimate goal of the contact investigation: treatment for contacts with LTBI or TB disease. Throughout the process of testing, treatment, and follow-up, appointment keeping and adherence to prescribed therapy should be monitored closely (see Module 9, Patient Adherence to Tuberculosis Treatment, for further information).
Figure 6.8 This a flow chart depicting the decisional analysis for the testing, treatment, and follow-up for contacts 4 years of age or older.
Figure 6.9 This a flow chart depicting the decisional analysis for the testing, treatment, and follow-up for contacts under 4 years of age.
Figure 6.10 This a flow chart depicting the decisional analysis
for the testing, treatment, and follow-up for immunosuppressed contacts.
|Study Questions 6.33-6.34
6.33. Which contacts should be evaluated for treatment for LTBI?
6.34. What is window period prophylaxis and when should it be used?