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Module 6: Contact Investigations for Tuberculosis
Answers To Study Questions

6.1. What is a contact investigation?

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

6.2. What are three reasons why a contact investigation is important?

A contact investigation is important to find contacts who
  • Have TB disease so that they can be given treatment, and further transmission of TB 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

It is not enough to simply find and test contacts of an infectious case. For a contact investigation to be successful, infected contacts should begin and complete a regimen of treatment for LTBI. Likewise, contacts with TB disease should begin and complete treatment for TB disease. A successful contact investigation can interrupt transmission and prevent future cases of disease.

6.3. For which TB cases should a contact investigation be conducted?

A contact investigation should be done whenever a patient is found to have or is suspected of having infectious TB disease. Infectiousness depends on a variety of factors, but is more likely when patients have cough, hoarseness, or other symptoms of pulmonary or laryngeal TB. Other factors that increase the likelihood of infectiousness include positive AFB sputum smear or culture results, a cavity on the chest radiograph, and inadequate or no treatment. It is very important that a contact investigation be conducted for such persons, because they are likely to have infected others.

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 smear-positive disease, and thus a lower risk of transmission, contact investigations for negative-smear cases usually should be conducted. Recent evidence suggests that transmission can occur in AFB sputum smear negative cases as well.

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. (Nontuberculous mycobacteria are not spread from person to person.)

6.4. For which TB cases should a source case investigation be conducted?

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)

6.5. What is the purpose of a source case investigation?

The purpose of a source case investigation is to determine

  • Who transmitted M. tuberculosis to the child, index patient, 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
  • Whether any others were infected by the source patient

6.6. How quickly should a contact investigation be carried out?

A contact investigation should begin as soon as TB is diagnosed or strongly suspected in a patient. The contact investigation interview should be initiated no more than 3 working days after the case is reported to the health department. Close contacts should be examined within 7 working days after the index case has been diagnosed. A prompt contact investigation is important because some contacts, such as young children or HIV-infected and other immunosuppressed contacts, may develop TB disease very quickly after being exposed to and infected with M. tuberculosis. High-risk contacts need timely treatment if they have been infected so they will not become ill with TB disease. Also, as time goes by, some contacts may become harder to locate; for example, homeless contacts can move frequently from shelter to shelter and contacts who are migrant workers often move from state to state. A prompt contact investigation increases the likelihood that all contacts will be found and evaluated. The sooner contacts are identified and evaluated, and can begin appropriate therapy, the less likely it is that transmission will continue.

6.7. Who is responsible for a contact investigation?

The health department is legally responsible for ensuring that a complete contact investigation is done for the TB cases reported in its area. Occasionally, some steps of the investigation may be performed by people outside the health department, under the supervision of the health department.

6.8. What is included in a contact investigation?

The contact investigation includes
  • Identifying and evaluating contacts
  • Treating any contacts found to have TB disease
  • Offering treatment for LTBI to infected contacts
  • Monitoring adherence to prescribed regimens and ensuring a system is in place to assess completion of treatment

6.9. What are the nine steps in a contact investigation?

A successful contact investigation requires the careful gathering and evaluation of detailed information by a process that includes these steps:
  1. Medical record review
  2. Patient interview
  3. Field investigation
  4. Risk assessment for M. tuberculosis transmission
  5. Decision about priority of contacts
  6. Evaluation of contacts
  7. Treatment and follow-up for contacts
  8. Decision about whether to continue testing
  9. Evaluation of contact investigation activities

Although these steps are presented in sequence, for the purposes of this module, it is important to remember that contact investigations do not always follow a predetermined sequence of events.

6.10. List seven types of information that should be collected during the medical record review.

The following information should be collected about the patient:

  • Site of TB disease
  • TB symptoms and approximate date symptoms began
  • Sputum smear and culture results, including the dates of specimen collection
  • Results of nucleic acid amplification testing (if available)
  • Chest x-ray results and date
  • TB treatment (medications, dosage, and date treatment was started)
  • Method of treatment administration (DOT or self-administered)

6.11. List five conditions that increase the likelihood that a patient is infectious.

Patients are more likely to be infectious if they
  • Have pulmonary or laryngeal TB
  • Are coughing (especially if they are producing a lot of sputum)
  • Have positive sputum AFB smear results and a culture positive for M. tuberculosis
  • Have chest x-ray results showing a cavity in the lung
  • Have had no treatment or have recently started treatment

6.12. Define the period of infectiousness and discuss how it is estimated.

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). Sometimes when it is difficult to obtain a reliable history from the patient about the onset of symptoms, the beginning of the infectious period is estimated to be earlier than the onset of symptoms. Estimating the period of infectiousness should be done by clinical and supervisory staff after a complete assessment of the information available.

The period of infectiousness ends when all the following criteria are met:

  • Symptoms have improved
  • The patient has been receiving adequate treatment for 2 to 3 weeks
  • The patient has had three consecutive negative sputum smears from sputum collected on different days

6.13. When should a patient interview be done?

The initial interview should occur no more than 3 working days after the case is reported to the health department because it is possible that some contacts may have already developed infectious TB disease. Also, as time goes by, some contacts may be harder to locate. If TB is diagnosed in the hospital, the health care worker should visit the patient in the hospital before the patient is discharged. Health care workers should remember to follow infection control precautions while visiting a potentially infectious TB patient. These precautions may include wearing a personal respirator.

6.14. List three reasons why the TB patient should be interviewed for a contact investigation.

For a contact investigation, there are three main reasons to interview the TB patient:
  • To find out more about the patient's symptoms to help determine the period of infectiousness
  • To find out places where the patient spent time while he or she was infectious
  • To identify the patient's contacts, get locating information for the contacts, and find out how often and how long the contacts were exposed to the patient while he or she was infectious

6.15. When conducting a contact investigation interview, from what three types of places should TB patients be asked to identify contacts?

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 recreation environments

6.16. What are some strategies the health care worker can use to conduct effective interviews?

For the patient interview to be effective and successful, a health care worker should

  • Explain to the patient the importance of the contact investigation for preventing and controlling TB
  • Ensure that the interview takes place under conditions that encourage effective communication
  • Establish the foundation for a good relationship with the patient based on mutual trust and understanding
  • Begin an assessment of the patient's knowledge, feelings, and beliefs about TB and educate patient
  • Ask open-ended questions

  • Have a clear understanding of the interview's objectives

  • Plan the interview so that each objective is given adequate time

  • Listen to the patient's concerns about TB and its treatment

  • Share information freely with the patient

6.17. What are four conditions that encourage effective interviews?

Because it is important to make the patient as comfortable as possible, the health care worker should ensure that the interview takes place under conditions that encourage effective communication. These conditions include
  • Arranging for privacy and maintaining confidentiality and assuring the patient that all information will be kept private
  • Creating an environment relatively free of distractions and interruptions
  • Listening attentively and respectfully to the patient (for example, sit down near the patient and use open, relaxed body language)
  • Being objective and nonjudgmental (for example, be patient, not accusatory, and never show frustration)

6.18. If the patient is not able to recall all of his or her contacts at the initial interview, what can the health care worker do to obtain more information about contacts?

The health care worker should realize that the patient may not be able to recall all of the names of possible contacts at the initial interview, especially if the interview occurs around the same time as the diagnosis. The health care worker should provide the patient with an opportunity to provide other contacts as they are remembered. The health care worker can encourage the patient to phone the health department if he or she remembers other contacts. In addition, the health care worker should schedule a follow-up interview with the patient to identify more contacts.

6.19. What is a field investigation?

A field investigation 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 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.

6.20. List six tasks a health care worker should perform during a field investigation.

During field visits, the health care worker should
  • Observe environmental characteristics such as room size, crowding, and ventilation, to estimate the risk of TB transmission

  • Identify additional contacts (especially children) and their locating information, such as phone numbers and addresses

  • Look for evidence of other contacts who may not be present at the time of the visit (for example, pictures of others who may live in or visit the house, shoes of others who may live in the house, or toys left by children)

  • Interview and skin test close contacts who are present and arrange for reading of the results

  • Educate the contacts about the purpose of a contact investigation, the basics of transmission, the risk of transmitting M. tuberculosis to others, and the importance of testing, treatment, and follow-up for TB infection and disease

  • Refer contacts who have TB symptoms to the health department for a medical evaluation, including sputum collection

6.21. List three general safety precautions that are recommended for the health care workers who conduct field investigations.

  • Wearing an identity badge with a current photo
  • Working in pairs when visiting a potentially dangerous area
  • Informing someone of your itinerary and expected time of return, especially if you anticipate problems

6.22. What three main factors should be considered in the risk assessment for TB transmission?

The risk of transmission depends on three main factors:
  • The infectiousness of the TB patient
  • The environmental characteristics of each place
  • The characteristics of the contact's exposure

Assessing this risk is crucial because it helps determine which contacts should be given higher priority for testing and evaluation.

6.23. Why is it important to know the period of infectiousness?

It is important to estimate the period of infectiousness because it helps determine which contacts have actually been exposed to TB. Contacts who spent time with the patient during the period of infectiousness are at higher risk for exposure and infection.

6.24. Name three environmental characteristics that would put contacts at higher risk of infection.

The risk of TB transmission in a particular place depends on the concentration of infectious droplet nuclei in the air -- that is, the number of droplet nuclei in a certain amount of air. The patient's infectiousness affects the concentration of droplet nuclei. In addition, the concentration of droplet nuclei depends on three environmental characteristics:

  • Size of the room
  • Amount of ventilation
  • Presence of air cleaning systems

Contacts are at higher risk of infection in a small, enclosed or crowded room that receives no fresh air. This is especially true if there are no air cleaning systems present.

6.25. Which contacts are at higher risk of becoming infected?

The following contacts are at higher risk for significant TB exposure, and so are most likely to become infected:
  • Contacts exposed to patients with a high degree of infectiousness based on the following factors: laryngeal or pulmonary TB, AFB sputum smear-positive, cavitary disease on chest x-ray, cough, positive culture for Mycobacterium tuberculosis
  • Contacts exposed to the patient in small or crowded rooms, areas that are poorly ventilated, or areas without air-cleaning systems
  • Contacts who frequently spend a lot of time with the patient, or have been physically close to the patient

6.26. Which contacts should be classified as close contacts and are most likely to be infected?

People who had close, regular, prolonged contact with the TB patient while he or she was infectious, especially in small, poorly ventilated places are close contacts and are most likely to be infected with TB. 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.

6.27. Which contacts are at high risk of developing TB disease if infected?

Some conditions (HIV infection, injection of illicit drugs, diabetes mellitus, silicosis, prolonged corticosteroid therapy, immunosuppressive therapy, certain types of cancer, severe kidney disease, certain intestinal conditions, and low body weight) increase the risk that TB infection will progress to TB disease. 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.

6.28. Which contacts should be considered high priority contacts for testing?

Close contacts (see answer 6.26) and contacts who are at high risk of developing disease if infected (see answer 6.27). Testing for TB infection and disease should begin with these high-priority contacts.

6.29. For all high-priority contacts, what procedures should be done during evaluation?

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.

In addition, any contact who has TB symptoms should be given both a chest x-ray and a sputum examination.

6.30. In what situation should tuberculin testing of contacts be repeated?

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, close 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.

6.31. Which contacts should be given a chest x-ray?

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.

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 that

  • Have TB symptoms
  • Are HIV-infected or have other immunosuppressed conditions
  • Are under 4 years of age

6.32. What is the purpose of a sputum examination and when should one be done?

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.

6.33. Which contacts should be evaluated for treatment for LTBI?

The following contacts should be evaluated for treatment of 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

6.34. What is window period prophylaxis and when should it be used?

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.

6.35. What factors show evidence of recent TB transmission?

Evidence of recent transmission is provided by any of the following factors:
  • A high infection rate among contacts
  • Infection in a young child
  • A skin test conversion in a contact
  • A secondary case of TB disease

An evaluation of this evidence will help determine whether testing should expand.

6.36. How is the infection rate calculated for a group of contacts?

To calculate the infection rate among a given group of contacts, the health care worker should follow these steps:
  1. Determine the number of contacts with newly identified positive skin tests.
  • Subtract the number of contacts with a documented previous positive skin test from the total number of contacts with a positive skin test (new or previously documented)
  1. Next, determine the total number of contacts without a documented previous positive skin test.
  • Subtract the number of contacts with a documented previous positive skin test from the total number contacts
  1. Finally, determine the infection rate.
    • Divide the number of contacts with a new positive skin test by the total number of contacts without a documented previous positive skin test

    • Multiply by 100; the resulting percentage is the infection rate for the group of contacts

6.37. What is the concentric circle approach?

The concentric circle approach is a method of testing contacts in order of their exposure time (close vs. other-than-close) and risk (high priority vs. low priority), with the close contacts and other contacts at high risk of developing TB disease tested first. In this approach, the original TB patient (the index case) is at the center. The circle is divided into three concentric rings to represent the three levels of risk: close (high risk), other-than-close (medium risk), and other-than-close (low risk). The circle is also divided, like a pie, into segments that represent the three types of environment where the contact may have taken place:

  • Household or residential
  • Work or school
  • Leisure or recreation environments

The highest-priority group, consisting of close contacts and of people at high risk of developing TB disease, is circle closest to the index circle. This means that this group is tested first. Close contacts can be found in each segment of the concentric circle (i.e., household or residential, work or school, and leisure or recreation environments). It is essential to test close contacts in all segments of the concentric circle, not just the household segment. Each of the circles represents groups of contacts, with the highest-priority groups nearest to the center and the lowest-priority groups farthest from the center. If there is evidence of transmission in one group, then the next outer circle of contacts should be tested, until there is no longer evidence of transmission.

6.38. List seven questions that should be answered in an evaluation of a contact investigation.

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?

6.39. As part of program evaluation activities, what will the result of a contact investigation help management staff determine?

Information from individual contact investigations will be compiled and evaluated by management staff as part of ongoing program evaluation activities. The results of these program evaluations are used to

  • Determine effectiveness
  • Identify areas in need of improvement
  • Prioritize program activities and resources

 
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