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Reichler MR, Reves R, Bur S, et al. Evaluation of Investigations Conducted to Detect and Prevent Transmission
of Tuberculosis. JAMA. 2002;287(8):991–995. doi:10.1001/jama.287.8.991
Context Contact investigations are routinely conducted by health departments
throughout the United States for all cases of active pulmonary tuberculosis
(TB) to identify secondary cases of active TB and latent TB infection and
to initiate therapy as needed in these contacts. Little is known about the
actual procedures followed, or the results.
Objectives To evaluate contact investigations conducted by US health departments
and the outcomes of these investigations.
Design, Setting, and Subjects Review of health department records for all contacts of 349 patients
with culture-positive pulmonary TB aged 15 years or older reported from 5
study areas in the United States during 1996.
Main Outcome Measures Number of contacts identified, fully screened, and infected per TB patient;
rates of TB infection and disease among contacts of TB patients; and type
and completeness of data collected during contact investigations.
Results A total of 3824 contacts were identified for 349 patients with active
pulmonary TB. Of the TB patients, 45 (13%) had no contacts identified. Of
the contacts, 55% completed screening, 27% had an initial but no postexposure
tuberculin skin test, 12% were not screened, and 6% had a history of prior
TB or prior positive tuberculin skin test. Of 2095 contacts who completed
screening, 68% had negative skin test results, 24% had initial positive results
with no prior test result available, 7% had documented skin test conversions,
and 1% had active TB at the time of investigation. Close contacts younger
than 15 years (76% screened vs 65% for older age groups; P<.001) or exposed to a TB patient with a positive smear (74% screened
vs 59% for those with a negative smear; P<.001)
were more likely to be fully screened. Close contacts exposed to TB patients
with both a positive smear and a cavitary chest radiograph were more likely
to have TB infection or disease (62% vs 33% for positive smear only vs 44%
for cavitary radiograph only vs 37% for neither characteristic; P<.001). A number of factors associated with TB patient infectiousness,
contact susceptibility to infection, contact risk of progression to active
TB, and amount of contact exposure to the TB patient were not routinely recorded
in health department records.
Conclusions Improvement is needed in the complex, multistep process of contact investigations
to ensure that contacts of patients with active pulmonary TB are identified
and appropriately screened.
Contacts of patients with infectious tuberculosis (TB) are at increased
risk of Mycobacterium tuberculosis infection and
disease. Therefore, contact investigations are recommended for all patients
with suspected or confirmed active pulmonary TB reported in the United States.1-3 The main goal of contact
investigations is to identify secondary cases of active TB and latent TB infection
among contacts so that they can begin therapy.1-4
Contact investigations are complex and involve many steps.4,5
Patients with suspected or confirmed TB are identified by clinicians and reported
to the health department. Case patients are then interviewed by health department
staff to obtain information about persons they may have had contact with when
potentially infectious. Following a process known as the concentric circle
approach, contacts are prioritized for investigation based on their amount
of exposure to the case patient.4 Persons judged
to have had the most contact are evaluated first, and the investigation is
expanded to include contacts with less exposure if infection rates in the
highest priority group are greater than the expected background rate in the
community (generally >15%-20%).4 Health department
staff notify contacts that they have been exposed to TB and the contact is
scheduled for a tuberculin skin test (TST). A follow-up test is recommended
3 months subsequent to last exposure, since TST conversion may occur up to
10 weeks following exposure.6 Chest radiograph
examinations are performed for all contacts with positive TST results and
for young children and immunocompromised contacts with negative TST results
to determine whether they have active TB.
Most health departments in the United States conduct contact investigations
for all patients with infectious TB as a routine part of their TB control
programs, but little is known about the actual procedures followed or the
results of those investigations. To address this knowledge gap, we conducted
a retrospective study of contact investigations performed in 1996 in 5 US
states. Our study had the following objectives: (1) to determine which data
are currently being collected during contact investigations, (2) to describe
contact investigation procedures, and (3) to evaluate contact investigation
results. Results of initiation and completion of treatment of latent TB infection
for these contacts has already been described.7
We solicited applications from health departments in the United States
that met 3 standards in 1996: (1) had a policy to conduct contact investigations
for all infectious TB patients, (2) maintained written records for all TB
patient and contact investigations, and (3) annually reported 50 or more patients
with TB. From 11 eligible health departments that applied for the study, 5
with the perceived best contact investigation programs and the best-organized
records were selected. Three study sites were large metropolitan areas, 1
comprised a large metropolitan area and 5 surrounding counties, and 1 comprised
10 counties containing small- or medium-size cities and surrounding rural
Data were abstracted from existing health department records for 360
patients aged 15 years or older with culture-positive pulmonary TB reported
to the Centers for Disease Control and Prevention national surveillance system
during 1996 (all patients at 4 sites and a random sample at 1 site), and for
all identified contacts of these patients. A list of contacts identified for
each patient was made by reviewing health department records. Investigations
with only tabular summary data recorded and those lacking individual contact
listings or records were excluded. The project was exempted from institutional
review board review because it involved the use of existing records.
Close Contact. Definitions for contact closeness differed between study areas, and
closeness was not recorded in written records for many contacts. For this
study, we defined contacts as "close" if they were members, visitors, or workers
in the case household (n = 699), or were friends (n = 145) or relatives (n
= 325) of the case; "not close" if they were not household contacts, friends,
or relatives; and "unknown" if type and place of contact were not specified
in the record.
Dates. The "date of last exposure" was defined as the approximate date of a
contact's last exposure to a patient, determined using the start date of the
patient's treatment (or date of collection of the first culture-positive specimen
in instances where the former was not available). The "date of clinical evaluation"
was defined as the date of collection of the first culture-positive specimen
from the patient.
Skin Test Converter. Defined as a contact with a negative TST at the time of initial evaluation
(or within the 2-year period prior to screening, if documented in health department
records) and a subsequent positive TST (≥5 mm induration and an increase
of ≥5 mm compared with the initial test).
Completely Screened. Contacts were considered completely screened if they had a TST performed
10 weeks or more after last exposure to the TB patient, positive TST results
at first testing, or active TB at the time of investigation.
Statistically significant differences (P<.05)
in risk variable responses were assessed with Mantel-Haenszel χ2 tests and χ2 tests for trend using Epi Info 6.04d (Centers
for Disease Control and Prevention, Atlanta, Ga).
A total of 3824 contacts were identified for 360 patients with active
pulmonary TB. No contact investigation results were available for 11 (3%)
patients and these patients were excluded from analysis. For the remaining
349 patients, the median number of contacts identified per patient was 5 (range
by study area, 3-14). The median number of contacts identified was higher
for patients who had both a positive smear and cavitary disease on chest radiograph
(8 vs 4 for other cases; P<.001). Forty-five (13%)
patients with contact investigations done had no contacts identified (range
by study area, 2%-19%), and an additional 38 (11%) had no close contacts identified
(range by study area, 11%-37%). The number of contacts identified per patient
ranged from 0 to 274 (interquartile range, 2-10). Of 5 investigations involving
more than 100 contacts, 1 was conducted in a school, 2 in homeless shelters,
1 in a large workplace, and 1 in an apartment complex.
Patients with no contacts identified were more likely to reside in a
homeless shelter (13% [6/45] vs 2% [6/304] of patients with contacts identified; P<.001). Only 6 (50%) of 12 patients residing in homeless
shelters had contacts identified. Patients with no contacts identified were
less likely to have written documentation that they were interviewed (56%
[25/45] vs 88% [268/304] of patients with contacts; P<.001).
Interview location was known for 164 (56%) of the 293 interviewed patients;
among these, patients with no contacts identified were less likely to have
been interviewed in their home (7% [1/14] vs 41% [62/150] of patients with
contacts; P = .01). The median time from patient
evaluation to report was longer for patients with no contacts identified (14
days vs 5 days for those with contacts identified). Demographic and clinical
characteristics of the 349 patients with TB and the 3823 identified contacts
are presented in Table 1.
Of 3824 contacts identified, 6% had a history of prior TB or prior positive
TST, 12% were not screened, 27% were incompletely screened (baseline TST but
no 3-month postexposure test), and 55% completed screening. Those at increased
risk of TB infection or progression to TB disease, such as close contacts
exposed to a patient with a positive smear (74% screened vs 59% for those
with a negative smear; P<.001) and close contacts
younger than 15 years (76% screened vs 65% for older age groups; P<.001), were more likely to complete screening. Contacts who were
not close were more likely to be fully screened if there was evidence of transmission
among close contacts to the same patient (data not shown).
Of the 1495 contacts not or incompletely screened, 1323 (88%) appear
to have been eligible for screening on the basis of: (1) being close contacts,
(2) evidence of transmission (active TB, infection in a child, TST conversion,
or infection rates ≥25%) among close contacts to the same patient, or (3)
too few close contacts (none or 1) of the patient screened to exclude transmission
in that patient's contact group.
Results for the 2095 contacts who completed screening are presented
in Table 2. Tuberculosis infection
(ie, initial TST positive or skin test converter) or disease was more likely
for close contacts (43% vs 32% for non-close contacts [P<.001] vs 17% for contacts of unknown closeness [P<.001]). Close contacts exposed to patients with both a positive
smear and cavitary disease diagnosed by chest radiograph (62%) were more likely
to have TB infection or disease than those with 1 or neither characteristic
(33% with positive smear only; 44% with cavitary disease diagnosed by radiograph
only; and 37% with neither; P<.001).
Of 678 contacts with a positive TST result or TB disease, chest radiograph
results were available for 598 (88%). The proportion of contacts with radiograph
results was higher for close contacts (95% vs 84% for non-close contacts; P<.001).
Figure 1 displays the overall
frequency with which a number of factors known to be associated with patient
infectiousness, contact exposure, contact susceptibility to TB infection,
and contact risk of progression to TB disease were recorded in written contact
No contacts were identified for 13% of the patients with culture-positive
pulmonary TB reported from our study areas. The number of persons potentially
exposed to a patient with TB varies considerably from patient to patient and
is dependent on the individual's household, work, and social environments.
Establishing a standard minimum number of contacts to be identified per patient
would not be useful, but nearly every case should have at least 1 contact,
with most having more than 1.
Ninety-three percent of patients in our study with no identified contacts
were alive at the time of diagnosis, and only half were known to have been
interviewed. Interviewing the patient to elicit contacts is the best (and
often the only) means of identifying potentially exposed persons, and it is
essential that all patients (or a suitable proxy for patients who are dead
at the time of diagnosis) be interviewed. The quality of TB case interviews
is dependent on a number of factors, including interviewer skill, interviewer
understanding of the patient's social setting, and the patient's ability and
willingness to share information.8 This is
well illustrated by several recent outbreaks in which initial patient interviews
failed to identify contacts in certain social networks that investigators
were not initially aware of, but whose presence was later established.8-11 The
2-week median interval from patient evaluation to report observed for patients
in our study who had no contacts identified may have decreased the number
of cases who could be located for an interview and may also have resulted
in lower interview quality. That patients with no identified contacts were
less likely to be interviewed at their place of residence is an intriguing
finding. One possible explanation could be that patients with no identified
contacts may have been less likely to have a usual place of residence, or
a safe home, in which to be interviewed. Further studies are needed to determine
whether conducting structured interviews, more than 1 interview, or at least
1 interview in the patient household (rather than in the clinic or hospital)
would minimize the number of patients for whom no contacts are identified.
We found that only 50% of patients with TB who resided in homeless shelters
had contacts identified. Previous studies have noted the limited usefulness
of traditional approaches to identifying contacts when the patient with TB
is homeless.12,13 Location-based
approaches, special efforts to establish trust, and improvements in the interview
technique have been suggested as ways to improve contact investigation in
this population.12,13 Social network
techniques for contact investigations involving homeless populations may be
another useful approach.11,14
Fewer than two thirds of identified contacts in our study completed
TST screening. The majority of incompletely screened and unscreened contacts
appear to have been in a priority group for screening. Since our study was
retrospective, we could not determine why some contacts were never screened
or why some initiated screening but did not complete it. Reasons could include
failure to locate certain contacts, failure of located contacts to respond
to requests for follow-up, or determination by health department staff that
a named contact was not a true contact. The large number of those incompletely
screened needs further exploration. One problem may be that health departments
lack "tickler" systems to remind personnel about the need to pursue contacts
for a follow-up test. There also may be problems motivating contacts to be
screened a second time.
The number of secondary infections that can be expected to arise from
patients with infectious TB in the United States today remains unknown. Our
study identified an average of 1.9 infected contacts per patient (2.6 per
smear-positive patient and 1.2 per smear-negative patient). Since complete
TST screening results were not available for many identified contacts, it
is likely that the actual number of infected contacts in the study areas is
higher than described herein.
Factors critical to optimal contact investigation, such as those associated
with case infectiousness, contact susceptibility to infection, type and amount
of contact exposure to the case, contact risk for progression to active TB
(including human immunodeficiency virus status), and contact history of prior
TB infection, were not recorded in written records for many or most contacts
in this study. These findings highlight the importance of written documentation
of key patient and contact characteristics, particularly those that are needed
to assess TB transmission risk and to establish priority in contact investigations.
A limitation of our study is that it was based on retrospective chart
review conducted at sites that had different procedures, definitions, and
data collection and management practices. However, we selected study sites
that were, in our opinion, among the best organized TB control programs in
the United States; thus, our data may underestimate the need for improvement
in the contact investigation process nationally.
A standard approach to TB contact investigation has the potential to
improve outcomes. To accomplish this, it will be necessary to (1) determine
the data that should be routinely collected during contact investigations;
(2) develop standard definitions for "contact" and "close contact"; (3) define
the duration, time period, and frequency of contact in various environments
that constitute exposure; (4) develop standard criteria for expanding contact
investigations; (5) define the extent of investigation needed in various epidemiologic
settings; and (6) develop effective data management systems for contact investigations.
A prospective study that attempts to provide the data needed to improve contact
investigation in these 6 ways is in progress in study areas in 4 US states.
Further studies should help define the ideal background and training of staff
who conduct contact investigations, determine the contact investigation model
(ie, outreach vs clinic-based) that works best in various settings, and determine
how to better motivate patients to comply with TST screening procedures.
Our results also highlight the need for greater awareness on the part
of the general medical community of the importance of promptly reporting patients
with suspected TB to facilitate contact identification and tracing. Greater
familiarity with the contact investigation process by physicians outside the
public health arena may also facilitate contact compliance with screening
and completion of treatment of latent TB infection—essential steps toward
interrupting TB transmission in the United States.
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