06/13/2007 - 22:00

Pathogens on a plane

Laura H. Kahn

Laura H. Kahn

A general internist who began her career in health care as a registered nurse, Kahn works on the research staff of Princeton University's ...

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In the movie
Snakes on a Plane, crates full of venomous snakes escape from the cargo hold of a 747 as
it flies from Honolulu to Los Angeles. The snakes terrorize and kill a large number of passengers.
While many snakes are deadly, invisible "pathogens on a plane" is a far scarier scenario. And worse
yet, pathogens such as viruses and bacteria really are on planes. Commercial aircraft could be
considered the twenty-first century equivalents of plague ships.

The recent scare involving the Atlanta-based lawyer with extremely drug-resistant tuberculosis
who flew in multiple aircraft from the United States to Europe is just one example of the role air
travel now plays in the potential transmission of deadly diseases. The conditions in commercial
aircraft for the spread of respiratory ailments such as influenza, severe acute respiratory
syndrome (SARS), and tuberculosis are perfect. Flying at 30,000 feet in a narrow hollow tube for
hours with people sneezing, coughing, and talking (and sometimes vomiting) while breathing dry,
recirculated air is a perfect set up for disease transmission.

Given these conditions, it shouldn't come as a surprise that influenza, SARS, and tuberculosis
have been transmitted on commercial aircraft. John Brownstein, Cecily Wolfe, and Kenneth Mandl
found evidence for the spread of influenza by air travel ("Empirical Evidence for the Effect of Airline Travel on Inter-Regional Influenza
Spread in the United States"
), and curtailing air travel has been proposed as one strategy to
control a flu pandemic ("Controlling Pandemic Flu: The Value of International Air Travel
Restrictions"
). Proximity to a person symptomatic with SARS appeared to be the greatest risk
factor for acquiring that disease on a plane ("Transmission of the Severe Acute Respiratory Syndrome on Aircraft").

Fortunately,
the risk of
acquiring tuberculosis on a plane appears to be low
. However, during one long flight, a highly
infectious individual with multidrug-resistant tuberculosis transmitted the disease to four
individuals seated within two rows of him and to two other persons seated further away ("Transmission of Multidrug-Resistant Mycobacterium Tuberculosis During a Long
Airplane Flight"
).

In other words, no one wants to sit for hours on a plane near a sick individual.

Respiratory illnesses typically spread via airborne and droplet routes. Airborne transmission
involves tiny particles containing pathogens that can remain suspended in the air for prolonged
periods of time. Tuberculosis typically spreads by this method. Droplet spread involves larger
particles that quickly settle out of the air. Some diseases (SARS and influenza among them) can
spread by both routes.

Some pathogens (the influenza virus, for example) can also exist on nonporous surfaces for
hours. Theoretically, people don't even need to sit near an infected individual to be exposed.
Touching contaminated surfaces such as door handles, window covers, and faucets and then later
touching a mucous membrane (eyes, etc.), can lead to inadvertent exposure. This is why quarantine
during an influenza pandemic won't work. Quarantine involves separating out healthy people who have
been potentially exposed to the illness. For influenza, people can be exposed and not know it.

So what should be done?

At the individual level, people who are sick with contagious respiratory illnesses shouldn't
fly. That, of course, is easier said than done--as evidenced by the recent tuberculosis crisis,
which illustrates why we are so dependent on a strong public health system, universal access to
primary care, and people's consciences--their sense of responsibility to themselves and others.

The Atlanta lawyer was diagnosed with tuberculosis only after receiving a chest X-ray for an
unrelated reason. What if he never had the chest X-ray? How many people might he have infected if
he hadn't been diagnosed until the disease was much more advanced?
Tuberculosis can be
transmitted by talking and sneezing
. There is considerable debate as to who was responsible in
overseeing his case, but clearly public health dropped the ball. (It worked, just not well.)

People flying with upper respiratory tract infections who cough and sneeze could be offered face
masks out of courtesy to fellow passengers. Aircraft could keep a supply of them on board for this
purpose. I used to keep a little bottle of 60 percent alcohol-based hand gel in my purse for
flights until a crack down on security prohibited carrying bottles of liquids and gels on board. I
would squirt a glob into my hand and rub my hands together vigorously after touching bathroom door
handles or window shades. Airlines could offer such gels to passengers--especially since not
everyone washes their hands regularly.

At a national level, nations have an obligation to make sure that their citizens don't spread
disease. International travelers should be required to show proof of vaccination against diseases
such as measles, mumps, rubella, diphtheria, and pertussis, and proof of a negative tuberculosis
skin test (or documentation of noninfectiousness in the event of a positive skin test) when
applying for passports. People who travel frequently to high-risk areas should be required to
document yearly tuberculosis skin tests before flying.

Millions of people fly annually. Unfortunately, air travel provides a vehicle for pathogens to
travel as well. We will assume that most people inadvertently spread their germs, although
deliberate spread is always a distinct possibility nowadays. With a global economy, we need to
ensure that air travel is safe; to do that, individuals, airlines, and nations must work together
to make sure that pathogens do not terrorize airline passengers.