Date: Fri, 3 Mar 1995 09:37:34 +0500
From: ghmcleaf{CONTRACTOR/ASPEN/ghmcleaf}%NAC-GATEWAY.ASPEN@ace.aspensys.com


MORBIDITY AND MORTALITY WEEKLY REPORT
Centers for Disease Control and Prevention
March 3, 1995
Vol. 44, No. 8

Exposure of Passengers and Flight Crew to Mycobacterium
tuberculosis on Commercial Aircraft, 1992-1995
     From January 1993 through February 1995, CDC and state health
departments completed investigations of six instances in which
passengers or flight crew traveled on commercial aircraft while
infectious with tuberculosis (TB). All six of these investigations
involved symptomatic TB patients with acid-fast bacillus (AFB)
smear-positive cavitary pulmonary TB, who were highly infectious at
the time of the flight(s). In two instances, Mycobacterium
tuberculosis isolated from the index patients was resistant to both
isoniazid and rifampin; organisms isolated from other cases were
susceptible to all antituberculous medications. In addition, in two
instances, the index patients were aware of their TB at the time of
travel and were in transit to the United States to obtain medical
care. However, in none of six instances were the airlines aware of
the TB in these passengers. This report summarizes the
investigations by CDC and state health departments and provides
guidance about notification of passengers and flight crew if an
exposure to TB occurs during travel on commercial aircraft.
Investigation 1. A flight attendant had documented tuberculin skin
test (TST) conversion in 1989 but had not received preventive
therapy (1). While working on numerous domestic and international
flights from May through October 1992, she developed a
progressively severe cough, and pulmonary TB was diagnosed in
November 1992. An investigation by CDC included TSTs of 212 flight
crew who worked with the flight attendant from May through October
and 247 flight crew who had not been exposed to her. The prevalence
of positive TSTs among flight crew exposed to the flight attendant
during August through October was higher than among crew exposed
from May through June (25.6% versus 4.1%; p less than 0.01) and
among unexposed flight crew (1.6%; p less than 0.01). TST
conversion was documented in two crew members exposed only in
August and October, respectively. TST positivity and conversions
were not associated with aircraft type, but were associated with
cumulative flight time exposure of greater than 12 hours. TST
reactivity was assessed in 59 passengers registered in the
airline's frequent flyer program who had traveled on flights worked
by the flight attendant with TB during August-October. Of these,
four (6.7%) were TST positive; all had traveled in October. The
investigation indicated that the index patient transmitted M.
tuberculosis to other members of the flight crew, but evidence of
transmission to passengers was inconclusive (1).

Investigation 2. During 1993, the Minnesota Department of Health
conducted an investigation of a foreign-born (i.e., born outside
the United States or Canada) passenger with pulmonary TB who
traveled in the first class section of an aircraft during a 9-hour
flight from London to Minneapolis in December 1992 (2). Of the 343
crew and passengers on the aircraft, TST results were obtained for
59 (61%) of 97 U.S. citizens and 20 (8%) of 246 non-U.S. citizens.
TSTs were positive for eight (10%) persons--all of whom had
received bacille Calmette-Guerin (BCG) vaccine or had a history of
past exposure to M. tuberculosis. The investigation indicated no
evidence of transmission of TB during the flight (2).

Investigation 3. In March 1993, a foreign-born passenger with
pulmonary TB traveled on a 1/2-hour flight from Mexico to San
Francisco. This investigation included efforts by the San Francisco
Department of Public Health to obtain information by mail from all
92 passengers on the flight; 17 persons could not be contacted
because of invalid addresses. TSTs were positive in 10 (45%) of the
22 persons who were contacted and completed TST screening; nine of
these TST-positive persons were born outside the United States. The
other was a 75-year-old passenger who may have become infected with
M. tuberculosis while residing outside the United States or during
a period when TB was prevalent in the United States. The San
Francisco Department of Public Health found no conclusive evidence
of transmission during this flight.

Investigation 4. In March 1993, CDC investigated a case of
pulmonary TB in a refugee who traveled on flights from Frankfurt,
Germany, to New York City (8-1/2 hours) and then to Cleveland, Ohio
(1-1/2 hours) (3). Of 219 passengers and flight crew on both
flights, 169 (77%) were U.S. residents; 142 (84%) of the U.S.
residents completed TST screening. TSTs were positive in 32 (23%),
including five persons who had converted from negative on initial
postexposure testing to positive on follow-up testing. Of the 32
TST-positive persons, 29 had received BCG or were born and had
resided in countries where TB is endemic, including all five TST
converters. The five passengers who were TST converters had been
seated in sections throughout the plane. Because none of the
U.S.-born passengers on this flight had TST conversions, the
investigation indicated that, although transmission could not be
excluded, the positive TSTs and conversions probably were
associated with prior M. tuberculosis infection, a boosted immune
response from prior exposure to TB, or prior BCG vaccination.

Investigation 5. In March 1994, a U.S. citizen with pulmonary TB
and an underlying immune disorder who had resided long term in Asia
traveled on flights from Taiwan to Tokyo (3 hours), to Seattle (9
hours), to Minneapolis (3 hours), and to Wisconsin (1/2 hour). Of
661 passengers on these four flights, 345 (52%) were U.S.
residents. The Wisconsin Division of Health contacted the 345 U.S.
residents and received reports about TST results from 87 (25%)
persons; of these, 14 (17%) had a positive TST. All 14 persons had
been seated more than five rows away from the index patient; nine
of these persons had been born in Asia (including two with a known
prior positive TST). Of the five who were TST-positive and
U.S.-born, one was known to have had a positive TST previously, two
had resided in a country with increased endemic risk for TB, and
two were aged greater than or equal to 75 years. The investigation
indicated that, although transmission of TB during flights could
not be excluded, the positive TSTs may have resulted from prior M.
tuberculosis infection.

Investigation 6. In April 1994, a foreign-born passenger with
pulmonary TB traveled on flights from Honolulu to Chicago (7 hours,
50 minutes) and to Baltimore (2 hours), where she lived with
friends for 1 month. During that month, her symptoms intensified;
she returned to Hawaii by the same route. Investigation in
Baltimore determined that TST conversion had occurred in the
22-month-old child of her friends. The four flights included a
total of 925 passengers and crew who were U.S. residents, of whom
755 (82%) completed TST screening; of these, 713 (94%) were
U.S.-born. The investigation by CDC indicated no evidence of
transmission on the flight from Honolulu to Chicago or the flight
from Chicago to Baltimore. Of the 113 persons who had traveled on
the flight from Baltimore to Chicago, TSTs were positive in three
(3%), including two who were foreign-born. However, of the 257
persons who traveled from Chicago to Honolulu (8 hours, 38
minutes), TSTs were positive in 15 (6%), including six who had
converted; two of these six persons apparently had a boosted immune
response, while the other four had been seated in the same section
of the plane as the index patient. Because of TST conversions among
U.S.-born passengers, the investigation indicated that
passenger-to-passenger transmission of M. tuberculosis probably had
occurred.

Reported by: C Hickman, MPH, KL MacDonald, MD, MT Osterholm, PhD,
State Epidemiologist, Minnesota Dept of Health. GF Schecter, MD, TB
Control Program, San Francisco Dept of Public Health; S Royce, MD,
DJ Vugia, MD, Acting State Epidemiologist, California State Dept of
Health Svcs. ME Proctor, PhD, JP Davis, MD, State Epidemiologist
for Communicable Diseases, Bur of Public Health, Wisconsin Div of
Health. S Bur, MPH, D Dwyer, MD, Maryland Dept of Health and Mental
Hygiene. Surveillance and Epidemiologic Investigations Br, and
Program Services Br, Div of Tuberculosis Elimination, National
Center for Prevention Svcs; Div of Field Epidemiology, Epidemiology
Program Office; Div of Quarantine, National Center for Infectious
Diseases, CDC.

Editorial Note: The investigations described in this report were
undertaken to determine whether exposure to persons with infectious
pulmonary TB was associated with transmission of M. tuberculosis to
others traveling on the same aircraft. Two of these investigations
indicated that transmission occurred (investigation 1, from flight
attendant to other flight crew, and investigation 6, from passenger
to passenger). In investigation 6, transmission occurred on the
return to Hawaii, when the index passenger was most symptomatic and
on the longest flight. All persons with TST conversions were seated
in the same section of the aircraft as the index passenger,
suggesting that transmission was associated with seating proximity.
Because the origins of all foreign-born passengers were countries
in which TB is endemic and/or where BCG vaccine is routinely used,
TST results from these passengers do not reliably represent recent
infection. Among persons who could be contacted during the other
investigations, low response rates constrained the interpretation
of findings from those investigations.

Investigations such as those described in this report are
subject to two substantial constraints. First, because the
investigation may be initiated several weeks to months following
the time of the flight and exposure, passengers may not be readily
located. With the exception of persons who are enrolled in frequent
flyer programs, airline companies do not routinely maintain
residence addresses or telephone numbers for passengers. Second,
the time elapsed between the flight and when public health
authorities and airline companies become aware of an exposure and
when passengers are notified and tested limits the use of TSTs to
assess for conversion. To interpret prevalent positive TST results,
other possible reasons for a positive TST result must be
considered, including prior exposure to TB, residence or birth in
countries in which TB is endemic, and BCG vaccination. In the
United States, an estimated 4%-6% of the total population is TST
positive (4), and in developing countries, the estimated prevalence
of M. tuberculosis infection ranges from 19.4% (in the Eastern
Mediterranean region) to 43.8% (in the Western Pacific region) (5).

To prevent exposures to TB aboard aircraft, when travel is
necessary, persons known to have infectious TB should travel by
private transportation (i.e., not by commercial aircraft or other
commercial carrier). In addition, patients with infectious TB
should at least be sputum smear-negative for AFB before being
placed in indoor environments conducive to transmission (6). Three
negative sputum smear examinations of specimens on separate days in
a person on effective anti-TB therapy indicate an extremely low
potential for transmission, and a negative culture virtually
precludes potential for transmission (6). Decisions about a TB
patient's infectiousness and ability to travel should be made on an
individual basis.

The risk for M. tuberculosis transmission on an aircraft does
not appear to be greater than in other confined spaces. Based on a
consideration of current evidence indicating low risk for
transmission of TB on aircraft, need for notification of passengers
and flight crew members may be guided by three criteria. First, the
person with TB was infectious at the time of the flight. Persons
who, at the time of flight, are symptomatic with AFB
smear-positive, cavitary pulmonary TB or laryngeal TB are most
likely to be infectious. Evidence of transmission to household and
other close contacts also indicates infectiousness. Second,
exposure was prolonged (e.g., duration of flight exceeded 8 hours).
Third, priority should be given to notifying passengers and flight
crew who were at greatest risk for exposure based on proximity to
the index passenger (for example, depending on the aircraft design,
proximity may be defined as seating or working in the same cabin
section as the infected passenger). Notification should be
conducted by the airline in coordination with local and state
TB-control programs.

References
1. Driver CR, Valway SE, Morgan WM, Onorato IM, Castro KG.
Transmission of M. tuberculosis associated with air travel. JAMA
1994;272:1031-5.
2. McFarland JW, Hickman C, Osterholm MT, MacDonald KL. Exposure to
Mycobacterium tuberculosis during air travel. Lancet 1993;342:112-
3.
3. Miller MA, Valway SE, Onorato IM. Assessing tuberculin skin test
conversion after exposure to tuberculosis on airplanes [Abstract].
In: Program and abstracts of the annual meeting of the American
Public Health Association. San Francisco: American Public Health
Association, 1993.
4. CDC. National action plan to combat multidrug-resistant
tuberculosis. MMWR 1992;41(no. RR-11):1-48.
5. Sudre P, ten Dam G, Kochi A. Tuberculosis: a global overview of
the situation today. Bull World Health Organ 1992;70:149-59.
6. American Thoracic Society. Control of tuberculosis in the United
States. Am Rev Respir Dis 1992;146:1623-33.