Self-Study Modules on Tuberculosis
Module 6: Contact Investigations for Tuberculosis
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
- 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
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:
- 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).
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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
- 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
- Did all identified cases complete an adequate treatment
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Centers for Disease Control and Prevention. Screening for tuberculosis
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Daley CL, Small PM, Schecter GF, et al. An outbreak of tuberculosis
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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