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TB Notes 1, 2000
A Decade of Notable TB Outbreaks: A Selected Review
by Scott B. McCombs, MPH
Deputy Chief, Surveillance and Epidemiology Branch
The Surveillance and Epidemiology Branch is charged with monitoring
TB morbidity and mortality in cooperation with state and local health
departments. One of the most fascinating and important parts of
our role is to assist our partners in responding to outbreaks of
TB when they occur. This article summarizes a cross-section of some
of the more notable outbreaks from the 1990s.
Extensive transmission of Mycobacterium tuberculosis
from a child (Curtis, Ridzon, Vogel, et al. N Engl J Med 1999;341:1491-1495).
Although young children rarely transmit TB, infectious TB was diagnosed
in a 9-year-old boy in North Dakota in July 1998. The child was
screened because extrapulmonary TB was diagnosed in his female guardian.
The child, who had come from the Republic of the Marshall Islands
in 1996, had bilateral cavitary TB. Because he was the only known
possible source of his guardian's TB, an investigation of the child's
contacts was undertaken. Family, school, day-care, and other social
contacts were notified of their exposure and given tuberculin skin
tests (TST). Of the 276 contacts tested, 56 had a positive TST (10
mm induration), including 3 of 4 household members, 16 of his 24
classroom contacts, 10 of 32 school-bus riders, and 9 of 61 day-care
contacts. A total of 118 persons received preventive therapy. The
9-year-old patient's twin brother had TB, but was deemed not infectious
on the basis of a negative sputum smear. This investigation showed
that children with TB, especially cavitary or laryngeal TB, should
be considered infectious, and that screening of their contacts may
Spread of Strain W, a highly drug-resistant strain of Mycobacterium
tuberculosis, across the United States (Agerton, Valway, Blinkhorn,
et al. Clin Infect Dis 1999; 29:85-92).
Strain W, a highly drug-resistant strain of Mycobacterium tuberculosis,
was responsible for large nosocomial outbreaks in New York in the
early 1990s. This article is a review of data from epidemiologic
investigations, national TB surveillance, regional DNA fingerprinting
laboratories, and the CDC Mycobacteriology Laboratory to identify
potential cases of TB due to Strain W. From January 1992 through
February 1997, 23 cases were identified in nine states and Puerto
Rico; 4 of the 23 cases transmitted disease to 10 other people.
Eighty-six contacts of the 23 cases were presumed to be infected
with Strain W. The authors conclude that Strain W TB cases will
occur throughout the United States as persons infected in New York
move elsewhere. CDC asked health departments to notify CDC of cases
of TB that were resistant to isoniazid, rifampin, streptomycin,
and kanamycin. The references for this article include citations
for earlier investigation results that have been published, including
this next one.
Transmission of a highly drug-resistant strain (Strain
W1) of Mycobacterium tuberculosis: Community outbreak and
nosocomial transmission via a contaminated bronchoscope (Agerton,
Valway, Gore, et al. JAMA 1997;278:1073-1077).
In 1995, eight patients with MDR TB were identified in South Carolina;
all were resistant to seven drugs and had matching DNA fingerprints
(Strain W1). Community links were identified for five patients (patients
1-5), but no links were identified for the other three patients (patients
6-8) except being hospitalized at the same hospital as one community
patient. Patients 5 and 8 both died of MDR TB less than one month
after diagnosis. Patients 6 and 7 each had one positive culture for
MDR TB; specimens were collected during bronchoscopy. Patient 6 had
a skin test conversion after bronchoscopy. Neither patient 6 nor patient
7 had a clinical course consistent with MDR TB, neither was treated
for MDR TB, and both are alive and well. There was no evidence of
laboratory contamination of specimens, transmission on wards, or contact
among patients. All four received bronchoscopy in the same month.
Observations revealed that bronchoscope cleaning and disinfection
was inadequate and led to subsequent false-positive cultures in patients
6 and 7, transmission of infection to patient 6 and active MDR TB
to patient 8.
>An outbreak involving extensive transmission of a virulent strain
of Mycobacterium tuberculosis (Valway, Sanchez,
Shinnick, et al. N Engl J Med 1998;338:633-639).
From 1994 to 1996 there was a large outbreak of TB in a small, rural
community with a population at low risk for TB. Twenty-one patients
with TB were identified; the DNA fingerprints of the 13 isolates available
for testing were identical. To determine the extent of transmission,
we investigated both the close and casual contacts of the patients.
Using a mouse model, we also studied the virulence of the strain of
Mycobacterium tuberculosis that caused the
outbreak. The index patient, the source patient, and one other patient
infected the other 18 persons. In five, active disease developed after
only brief, casual exposure. There was extensive transmission from
the three patients to both close and casual contacts. Of 429 contacts,
311 (72%) had positive skin tests, including 86 documented skin test
conversions. The growth characteristics of the strain involved in
the outbreak greatly exceeded those of other clinical isolates of
M. tuberculosis. The extensive transmission
of TB in this outbreak may have been due to the increased virulence
of the strain rather than to environmental factors or patient characteristics.
Image 1: Figure holding a magnifying glass.
A nosocomial outbreak of multidrug- resistant tuberculosis (Kenyon,
Ridzon, Luskin-Hawk, et al. Ann Intern Med 1997;127:32-36).
This article details an outbreak of seven cases of MDR TB (in six
patients and one health care worker, all of whom had AIDS) that
occurred in a hospital in Chicago. The hospital had a respirator
fit-testing program but no acid-fast bacilli isolation rooms. All
seven M. tuberculosis isolates had matching DNA fingerprints.
Of patients exposed to M. tuberculosis, those who developed
TB had lower CD4+ T-lymphocyte counts and were more likely to be
ambulatory than those who did not. Of 74 exposed health care workers,
the 11 who converted their skin tests were no more likely than those
who did not convert to report that they always wore a respirator
with a HEPA filter. Transmission of M. tuberculosis occurred
in a hospital that did not have recommended isolation rooms. A respirator
fit-testing program did not protect health care workers in this
Outbreak of drug-resistant tuberculosis with second-generation
transmission in a high school in California (Ridzon, Kent, Valway,
et al. J Pediatr 1997;131:863-868).
In the spring of 1993 four students in a high school were diagnosed
with TB resistant to isoniazid, streptomycin, and ethionamide. A
retrospective cohort study with case investigation and skin test
screening was conducted in the school of approximately 1,400 students.
DNA fingerprinting of available isolates was performed. Eighteen
students with active TB were identified. Through epidemiologic and
laboratory investigation, 13 cases were linked. Nine of the 13 had
positive cultures for M. tuberculosis with isoniazid, streptomycin,
and ethionamide resistance, and all eight available isolates had
identical DNA fingerprints. No staff member at the school had TB.
One student remained infectious for 29 months and was the source
case of the outbreak. Another student was infectious for 5 months
before diagnosis and was a treatment failure. This student subsequently
developed additional resistance to rifampin and ethambutol. The
initial skin test screening found 292 of 1263 (23%) students tested
had a positive TST. Risk of infection was highest among twelfth
graders and classroom contacts of the two students with prolonged
infectiousness. An additional 94 of 928 (10%) students tested later
had a positive TST; 22 were classroom contacts of the student with
treatment failure and 21 of these were documented TST conversions.
This article documents extensive transmission of drug-resistant
TB along with missed opportunities for prevention and control of
the outbreak. Prompt identification of TB cases and timely interventions
should help reduce these problems.
Transmission of multi-drug resistant Mycobacterium tuberculosis
during a long airplane flight (Kenyon, Valway, Ihle, et al. N Engl
J Med 1996;334:933-938).
In April 1994 a passenger with infectious MDR TB traveled on commercial-airline
flights from Honolulu to Chicago and from Chicago to Baltimore and
returned one month later. We sought to determine if this passenger
infected any of her contacts on this extensive trip. Of 925 people
on the airplanes, 802 responded to a request to complete a questionnaire
and be screened by tuberculin skin test. All 11 contacts with positive
TST who were on the April flights and 2 of 3 contacts with positive
TST on the Baltimore-to-Chicago flight in May had other risk factors
for tuberculosis. More contacts on the 8.75 hour flight from Chicago
to Honolulu had a positive TST than on the other three flights.
Of 15 contacts with a positive TST on the Chicago-to-Honolulu flight,
six (four with skin-test conversions) had no other risk factors;
all six sat in the same section as the index patient. Passengers
seated within two rows of the index patient were more likely to
have a positive TST than those in the rest of the section. Transmission
of M. tuberculosis in this setting involved a highly infectious
passenger, a long flight, and close proximity of contacts to the
The Division of TB Elimination and our partners in state and local
health departments have benefitted tremendously from what has been
learned from these and other outbreaks. Our continued cooperation,
diligence, and timely systematic response to future outbreaks are
critical to our eventual success in eliminating TB from the United