Self-Study Modules on Tuberculosis
Module 6: Contact Investigations for Tuberculosis
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
- 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
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
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.
- 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
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 (see page
64), 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
- 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.
When to Conduct and How to Prioritize Contact Investigations
|AFB sputum smear-positive
|Conduct contact investigation
|AFB sputum smear-positive
|Conduct contact investigation (if culture is not TB and
clinical TB ruled out, stop contact investigation)²
|AFB sputum smear-negative
|Conduct contact investigation
||Lower than AFB sputum smear-positive
|AFB sputum smear-negative
|Conduct contact investigation if strong clinical suspicion³
(if culture is not TB and clinical TB ruled out, stop contact
||Lower than AFB sputum smear-positive
|AFB sputum smear-negative
|Do not conduct a contact investigation if TB is ruled out
||Low if "clinical TB"
||Ensure pulmonary TB ruled out
Special laboratory tests (for example, nucleic acid amplification
tests) have been used in some areas to more quickly detect M.
- 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.
- Contact investigations are not performed for diseases caused
by nontuberculous mycobacteria.
- 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).
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
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
- 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
- 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
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
- Medical record review
- Patient interview
- Field investigation
- Risk assessment for M. tuberculosis transmission
- Decision about priority of contacts
- Evaluation of contacts
- Treatment and follow-up for contacts
- Decision about whether to expand testing
- 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
6.3. For which TB cases should a contact investigation
6.4. For which TB cases should a source case investigation
6.5. What is the purpose of a source case investigation?
6.6. How quickly should a contact investigation be carried
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?
|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?
|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
- 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.
- 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.
- 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
- How should the case(s) be prioritized in terms of conducting
a contact investigation?