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Module 6: Contact Investigations for Tuberculosis
Reading Material

Goals of a Contact Investigation

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

LTBI is 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.

People exposed to someone with infectious TB disease are called the contacts of that person; exposure to TB is time spent with or near such a person and is determined by the duration, proximity, and intensity of time spent with the person. Contacts generally include family members, roommates or housemates, close friends, coworkers, classmates, and others. Health care workers usually identify contacts by interviewing the person who has TB and by visiting the places where that person spends time regularly.

Note: Contacts are often given a medical evaluation and may receive treatment for LTBI or TB disease; however, in this module, we reserve the term "patient" for the index patient, a person with suspected or confirmed TB disease who is the initial case reported to the health department.

Why Is a Contact Investigation Important?

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
Some contacts who become infected with M. tuberculosis develop TB disease before the contact investigation is started. Doing a contact investigation is one of the best ways to find people who have TB disease. Data indicate that seven to eight cases of TB disease are found for every 1000 contacts who are evaluated. The rate of having TB disease is 75 times higher among contacts than among the general population.

It is also important to find infected contacts who do not yet have TB disease, so that they can be given treatment for LTBI. Contacts are a high-priority group for treatment for LTBI because they are at high risk of being infected with M. tuberculosis, and if infected, they are at high risk of developing disease. On average, about 20% of contacts are found to have TB infection, but in some contact investigations as many as 80%-100% of the close contacts may be infected.

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.

High-risk contacts are contacts who are at a particularly high risk of developing TB disease if they have become infected with M. tuberculosis. Contacts who are less than 4 years of age or immunosuppressed, e. g., infected with the human immunodeficiency virus (HIV), or have certain other medical conditions, should be given treatment for LTBI until it becomes clear whether they have actually been infected. Because such persons may quickly develop TB disease, it is very important to identify them as high-risk contacts and manage them accordingly.

When Is a Contact Investigation Done?

A person with suspected or confirmed TB disease who is the initial case reported to the health department is called the index patient. An index patient could be diagnosed in a health department clinic. More often, a TB case is reported to the health department by a hospital, laboratory, private clinician's office, correctional facility, or other institution where the patient is diagnosed.

In general, a contact investigation should be done whenever a patient is found to have or is suspected of having infectious TB disease (Table 6.1) (see Module 5, Infectiousness and Infection Control, for additional information). Infectiousness depends on a variety of factors, but is more likely when patients have

  • Cough
  • Hoarseness
  • Other symptoms of pulmonary or laryngeal TB

Other factors that increase the likelihood of infectiousness include

  • Positive acid-fast bacilli (AFB) sputum smear or culture results
  • A cavity on the chest radiograph
  • Inadequate or no treatment

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. Recent evidence suggests that transmission can occur in these AFB sputum smear-negative cases as well. Moreover, a negative AFB sputum smear may be the result of a poor quality sputum specimen. Contact investigations for cases with negative AFB sputum smears are a lower priority than those with positive AFB sputum smears (Table 6.1). Decisions about the prioritization of contact investigations should be made by supervisory clinical and management staff. 

There are some instances in which contact investigations are not performed (Table 6.1). 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 (Table 6.1). (Nontuberculous mycobacteria are not spread from person to person.) When information about the type of mycobacteria causing disease in a particular person is not available at the time the case is reported to the health department, a contact investigation should be initiated if TB is strongly suspected, especially if AFB sputum smears are positive. When the culture results are available and only nontuberculous mycobacteria are identified, the patient should be evaluated clinically to rule out TB disease, and the contact investigation is then usually stopped.

Table 6.1
When to Conduct and How to Prioritize Contact Investigations

Site Bacteriology Action Priority
Pulmonary/
laryngeal/
AFB sputum smear-positive

Culture positive

Conduct contact investigation High
Pulmonary/
laryngeal
AFB sputum smear-positive

Culture pending

Conduct contact investigation (if culture is not TB and clinical TB ruled out, stop contact investigation) High
Pulmonary/
laryngeal
AFB sputum smear-negative

Culture positive

Conduct contact investigation Lower than AFB sputum smear-positive
Pulmonary/
laryngeal
AFB sputum smear-negative

Culture pending

Conduct contact investigation if strong clinical suspicion (if culture is not TB and clinical TB ruled out, stop contact investigation) Lower than AFB sputum smear-positive
Pulmonary/
laryngeal
AFB sputum smear-negative

Culture negative

Do not conduct a contact investigation if TB is ruled out Low if "clinical TB"
Extrapulmonary --- Ensure pulmonary TB ruled out N/A
  1. Young children with TB disease are rarely infectious so a contact investigation is generally not conducted for them. However, young children with pulmonary TB disease should be evaluated for infectiousness and contact investigation may be warranted in some circumstances. A source case investigation should be conducted.
  2. Contact investigations are not performed for diseases caused by nontuberculous mycobacteria.
  3. Strong clinical suspicion refers to a patient with symptoms and radiographic findings consistent with TB disease (and no other diagnosis to account for these findings).

Special laboratory tests (for example, nucleic acid amplification tests) have been used in some areas to more quickly detect M. tuberculosis 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 (Table 6.1). (Although rare, it is possible for children to transmit M. tuberculosis to others and a contact investigation may be warranted in some circumstances.)

However, when a young child has TB infection or disease, we know that M. tuberculosis was transmitted relatively recently. For example, a 2-year-old child with TB disease must have been exposed to someone with TB disease during the past 2 years. The person who is the source of this exposure is called the source patient. A source patient is 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 an index patient.

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)

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

Prioritizing Contact Investigations

Setting priorities between two or more contact investigations is a decision that should be made by supervisory clinical and management staff based on the likelihood of infectiousness of index case patients (Table 6.1). If program resources are limited, priority for resources and staff time should be placed on identifying contacts and conducting follow-up with contacts

  • Who were exposed to the TB patients that are most likely to be infectious
  • Who are at highest risk for TB infection or TB disease

For example, a patient with pulmonary TB who was coughing for 3 months before receiving treatment and who has positive AFB sputum smears is much more likely to be infectious than a patient who has negative AFB sputum smears and who has rarely been coughing. Therefore, the first patient is a higher priority for a contact investigation. In addition, for a patient who lives in a residential shelter for people with AIDS, the priority for a contact investigation is also high because contacts infected with HIV are at very high risk of developing TB disease if exposed to and infected with M. tuberculosis. Thus, decisions about prioritizing contact investigations depend on the circumstances and on the guidelines of the particular health department, and should be made by supervisory clinical and management staff.

In some situations, a contact investigation should not be done. For example, time and resources are often not devoted to a contact investigation if the patient is found to have extrapulmonary TB only, with no risk of transmission. In some instances, however, a source case investigation is done for index patients with extrapulmonary TB (for example, when the index patient is a child).

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.

For a contact investigation to begin quickly, suspected and confirmed TB cases must be reported promptly to the health department. In fact, laboratories, hospitals, private clinicians, and other groups serving people with TB are required by law to report this information to local and state public health departments.

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. This 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

Occasionally, some steps of the investigation may be performed by people outside the health department, under the supervision of the health department. For example, if a patient in a hospital is found to have TB disease, infection control and employee health staff from the hospital may evaluate staff and some patients who were exposed, whereas the health department staff would evaluate contacts outside the institution. At a minimum, health department staff should work with hospital staff to plan the contact investigation and receive a report of the results (for example, the number of contacts identified, the number with newly documented infections, the number with TB disease, detailed treatment plans, and documentation of therapy administered and completed).

Steps in a Contact Investigation

A successful contact investigation requires the careful gathering and evaluation of detailed information, often involving many people. In general, contact investigations follow 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 expand 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.
 

    Study Questions 6.1-6.9

    6.1. What is a contact investigation?

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

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

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

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

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

    6.7. Who is responsible for a contact investigation?

    6.8. What is included in a contact investigation?

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

    Answers 


     
    Case Study 6.1
    Jung Hu is a 3-year-old child who has been diagnosed with TB meningitis. Jung and his parents immigrated from China one year ago, along with his paternal grandmother. Jung does not have pulmonary or laryngeal TB disease, and a sputum specimen collected by gastric aspirate does not show any acid-fast bacilli (AFB). Jung's TB disease is reported to the health department and he is started on an appropriate TB drug regimen.
    • Should a contact investigation be done with Jung as the index patient? Why or why not?
    • Should a source case investigation be done? What would be the purpose of this investigation?

    Answers 


     
    Case Study 6.2
    You are a clinical TB case manager at a busy clinic in Smith County. Three new TB cases have been assigned to you. You need to review their charts and assign them to contact investigators.
    1. Mr. Garcia is a 35-year-old agricultural worker diagnosed by a local private physician with extrapulmonary TB of the kidneys. He lives with his wife and 3 children (5 years, 3 years, and 9 months old) in a small, rented house in a rural part of the county. He rides to work every day in a van with 7 other agricultural workers.
    2. Mr. James is a 72-year-old widower who lives alone on the south side of town. He drives himself to the local retirement center 2 miles from his house for bingo and poker four times a week. He was recently evaluated by the retirement center physician because he complained of a productive cough, shortness of breath, fatigue, and weight loss. He is AFB sputum smear-positive and his culture is pending. His chest x-ray shows a cavity in the right upper lobe. He started a four-drug regimen.
    3. Mrs. Osaka is a 25-year-old woman who recently arrived from Japan. She was seen in the Smith County Clinic complaining of shortness of breath, a weak nonproductive cough, fatigue, and weight loss. Her AFB sputum smear was negative and her culture is pending. She lives with her husband and parents in a large apartment off Broadway. She is currently unemployed. She started a four-drug regimen.
    • For which case(s) should a contact investigation be conducted?
    • How should the case(s) be prioritized in terms of conducting a contact investigation?

    Answers 


 
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