Evaluation of Investigations Conducted to Detect and Prevent
Transmission of Tuberculosis
JAMA. 2002;287:991-995
Mary R. Reichler, MD; Randall Reves, MD, MSc; Sarah Bur, RN, MPH;
Virginia Thompson, RN; Bonita T. Mangura, MD; Josie Ford, RN; Sarah E. Valway,
DMD, MPH; Ida M. Onorato, MD; for the Contact Investigation Study Group
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.
JAMA. 2002;287:991-995
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
METHODS
Study Areas
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 areas.
Study Design
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.
Study Definitions
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.
Data Analysis
Statistically significant differences (P<.05)
in risk variable responses were assessed with Mantel-Haenszel 
2 tests and 2 tests for trend using Epi Info 6.04d (Centers for
Disease Control and Prevention, Atlanta, Ga).
RESULTS
Cases and Identified Contacts
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.
Skin Test Screening
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.
Screening Results
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).
Data Collected During Contact
Investigations
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 records.
COMMENT
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.
Author/Article Information
Author Affiliations: Division of
Tuberculosis Elimination, National Center for HIV, STD, and TB Prevention,
Centers for Disease Control and Prevention, Atlanta, Ga (Drs Reichler, Valway,
and Onorato); Denver Public Health, Denver, Colo (Dr Reves); the Maryland
Department of Health and Mental Hygiene, Baltimore, (Ms Bur); Massachusetts
Department of Public Health, Jamaica Plain (Ms Ford); Mississippi State
Department of Health, Jackson (Ms Thompson); New Jersey Department of Health
and Senior Services, Trenton, and New Jersey Medical School National
Tuberculosis Center, Newark (Dr Mangura).
Corresponding Author and Reprints:
Mary R. Reichler, MD, Mailstop E-10, DTBE, Centers for Disease Control and
Prevention, 1600 Clifton Rd, Atlanta, GA 30333 (e-mail: [log in to unmask]).
Author Contributions: Study concept and design:
Reichler, Reves, Bur, Valway, Onorato.
Acquisition of data: Reves, Bur, Thompson, Mangura, Ford.
Analysis and interpretation of
data: Reichler, Reves, Bur,
Mangura, Valway, Onorato.
Drafting of the manuscript: Reichler, Mangura, Ford.
Critical revision of the
manuscript for important intellectual content: Reichler, Reves, Bur, Thompson, Mangura, Valway, Onorato.
Statistical expertise: Reichler.
Obtained funding: Reves, Bur, Mangura.
Administrative, technical, or
material support: Reves, Mangura, Ford,
Valway.
Study supervision: Ford, Valway, Onorato.
Contact Investigation Study
Group Members: Denver Public Health
Department and Colorado Department of Health and Environment: Patty Calixto,
Mohammed Malakouti, Bessy Natareno Garcia, Juanita Diaz; Maryland Department of
Health and Mental Hygiene: Nancy Baruch, Deirdre Thompson; Massachusetts
Department of Public Health: Janice Boutotte, Denise O'Connor, Sue Etkind,
Margaret Harding; Mississippi State Department of Health: J. M. Holcombe; New
Jersey Department of Health and Senior Services: Ken Shilkret, Janet de Graaf;
New Jersey Medical School National Tuberculosis Center: Mark Wolman.
Funding/Support: Funding for this project was provided through a supplement to the
Centers for Disease Control and Prevention Tuberculosis Cooperative Agreement.
Previous Presentation: Preliminary data from this study were presented at the
International Union Against Tuberculosis and Lung Disease Annual Meeting,
Bangkok, Thailand, November 1998; the Infectious Diseases Society of America
Annual Meeting, Denver, Colo, November 1998; the International Union Against
Tuberculosis and Lung Disease Annual Meeting, Madrid, Spain, September 1999;
the Infectious Diseases Society of America 37th Annual Meeting, Philadelphia,
Pa, November 1999; and the American Thoracic Society Conference, Toronto, Ontario,
May 2000.
Acknowledgment: We thank Elsa Villarino, MD, MPH, Rick O'Brien, MD, and Peter
Bing, MD, for their helpful comments on the manuscript.
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Edward E.
Rylander, M.D.
Diplomat American
Board of Family Practice.
Diplomat American
Board of Palliative Medicine.