Self-Study Modules on Tuberculosis
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
- Evaluating these people for latent TB infection (LTBI) and
- Providing appropriate treatment for those with LTBI and TB
6.2. What are three reasons why a contact investigation
A contact investigation is important to find contacts
- 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
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
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
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
- Whether any others were infected by the source patient
6.6. How quickly should a contact investigation be carried
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
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:
- 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 continue 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.
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
- Results of nucleic acid amplification testing (if available)
- Chest x-ray results and date
- TB treatment (medications, dosage, and date treatment was
- 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
- Symptoms have improved
- The patient has been receiving adequate treatment for 2 to
- 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
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
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
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
- Listening attentively and respectfully to the patient (for
example, sit down near the patient and use open, relaxed body
- 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
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
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
Refer contacts who have TB symptoms to the
health department for a medical evaluation, including sputum
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
- 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
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
- 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
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
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
- 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
The following contacts should be evaluated for treatment
- 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
6.36. How is the infection rate calculated for a group
To calculate the infection rate among a given group of
contacts, the health care worker should follow these steps:
- Determine the number of contacts with newly identified positive
- 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)
- 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
- Finally, determine the infection rate.
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
- 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