UPDATES FROM THE SURVEILLANCE, EPIDEMIOLOGY,
AND OUTBREAK INVESTIGATIONS BRANCH
Year in Review: TB Outbreak Investigations
2003
Like the previous year, 2003 was a busy year for the Outbreak
Investigations Team (OIT) in DTBE’s Surveillance, Epidemiology,
and Outbreak Investigations Branch (SEOIB). During 2003, DTBE’s
Outbreak Evaluation Unit received 34 reports of TB outbreak activity.
In response to these, at the local jurisdictions’ request, the
OIT conducted six on-site Epi-Aid investigations (five national
and one international) and provided technical assistance in response
to three other reports. The Field Services and Evaluation Branch
(FSEB), the Communications, Education, and Behavioral Studies
Branch (CEBSB), and the Clinical and Health Systems Research Branch
(CHSRB) collaborated with OIT on these investigations.
The highlights of the year’s outbreak investigations were the
predominant outbreak investigations among homeless persons and
the use of the Quantiferon®-TB test (QFT) as part of
a research protocol for detection of latent TB infection (LTBI)
during large contact investigations and outbreaks.1
The results of QFT use will be described later once the study
is completed and data are analyzed.
During 2003, the OIT conducted three Epi-Aid investigations among
homeless persons (in Seattle, Washington; Portland, Maine; and
Wichita, Kansas). Although the three situations were similar in
involving homeless persons, there were differences in the demographic
characteristics and risk factors among these groups that warranted
the use of a variety of innovative strategies by the epi-investigation
teams to conduct detailed and thorough contact investigations.
The first of these investigations was conducted during May 2002
– September 2003 in Seattle, Washington, where Public Health –
Seattle-King County (PH-SKC) found 44 persons with outbreak-associated
TB. All but three of the outbreak-associated patients were homeless
at the time of diagnosis; 43 (98%) were born in the United States,
34 (77%) were male, 21 (48%) were American Indian or Alaska Native,
and 17 (39%) were black. Of the 38 (86%) persons with pulmonary
disease, 23 (61%) had acid-fast bacilli detected on sputum smear
at diagnosis. Seven (16%) outbreak-associated patients were also
infected with human immunodeficiency virus (HIV). In January 2003,
a CDC Epi-Aid team, along with PH-SKC, assisted in finding contacts
at highest risk for exposure. Investigators reinterviewed outbreak
patients and health care providers serving homeless facilities
to find additional patient contacts. Sites of transmission were
determined by review of homeless facility intake registries for
the presence of persons with infectious TB disease and the rates
of positive tuberculin skin test (TST) results among staff and
clients. Exposed cohorts were found at three sites of transmission.
The cohort prioritized for intensive testing included 385 contacts
from three homeless facilities and 86 other contacts named by
patients or health care providers. In February 2003, PH-SKC began
an intensive effort to test the high-priority cohort for TB disease
and LTBI in the TB clinic and at homeless facilities; this included
symptom review, chest radiograph, sputum examination and culture,
TST, and voluntary HIV counseling and testing. During February–September
2003, approximately 380 contacts were screened with chest radiograph
or sputum culture or both. Of the 44 outbreak-associated patients,
20 were reported during this time, and 11 (55%) were found through
these intensive and focused screening efforts, limiting the amount
of time these persons were exposing others in the community.2
The second investigation was conducted in Portland, Maine, which
is a low-incidence state. During June 2002 – July 2003, seven
men with pulmonary TB disease in Portland, Maine, were reported
to the Maine Bureau of Health (MBH). Six were linked through residence
at homeless shelters; four had matching genotypes. As of November
20, 2003, the investigation had found 1,069 contacts, 36 (3%)
of whom reported having a positive TST result previously. Among
the 1,033 persons eligible for a TST, 648 (63%) received at least
one test, and 56 (9%) of these had a positive result; 15 (27%)
of the 56 are receiving, and one completed, therapy for LTBI.
A total of 163 (15%) contacts had chest radiographs; no additional
active cases were detected. Delayed diagnosis and missed opportunities
for TB prevention were determined to be major contributors for
TB transmission. Prompt investigation and identification of contacts
likely prevented further spread of TB.3
The third investigation was conducted in Sedgwick County, Kansas,
where in 2003, TB genotyping detected a potential five-case cluster.
Traditional name-based TB contact investigations had not revealed
epidemiologic links. An Epi-Aid team conducted a targeted investigation
in collaboration with the Sedgwick County health department to
determine location-based links and the extent of transmission,
and recommend TB control measures. Medical records were reviewed
to determine TB patients’ infectious periods, followed by reinterviews
about their activities and locations while contagious. Homeless
facilities’ logs were reviewed to find common stays between contagious
TB patients and other facility clients. Clients were divided into
exposure categories according to number of common stays. Location-based
contacts received TB screening, including a TST. TB genotyping
provided the impetus to investigate locations linking the patients
in this cluster. The investigation determined plausible transmission
sites and directed the county’s TB control strategies, which now
include mandatory TB screening at all homeless facilities.
As the TB control community collectively moves towards TB elimination
in the United States, it is important to remember that TB is receding
back into the traditional “pockets” of infection as evidenced
by the TB outbreaks among homeless persons described above. These
and other high-risk, hard-to-reach populations will provide challenges
to all of us. We should remain vigilant and closely monitor TB
control efforts, especially in population groups at high risk
for TB. Moreover, we all face the additional challenge of
reduced public health resources. It is now more important than
ever for public health organizations at the local, state, and
national levels to continue to work closely together against TB.
Health departments may request DTBE assistance with outbreaks,
cluster investigations, or other instances of TB transmission
by contacting their DTBE Program Consultant. Such assistance
may take the form of programmatic consultation, technical assistance,
or on-site assistance (for example, an Epi-Aid). Your partners
in DTBE are eager to work with you to achieve our common goal
of TB elimination.
—Reported by Kashef Ijaz, MD, MPH
Div of TB Elimination
References
1. CDC. Guidelines for using the QuantiFERON®-TB test
for diagnosing latent Mycobacterium tuberculosis
infection. MMWR 2003; 52 (No. RR-2: [15-18]).
2. CDC. Public health dispatch: Tuberculosis outbreak among homeless
persons-King County, Washington, 2002-2003. MMWR 2003;
52(49);1209-1210.
3. CDC. Public health dispatch: Tuberculosis outbreak in a homeless
population-Portland, Maine, 2002-2003. MMWR 2003; 52(48);1184-1185.
