Illness associated with air travel is uncommon, but is generally related to changes in air pressure, humidity and oxygen concentration, relative immobility during flights (see Chapter 6), or close proximity to other passengers with certain communicable diseases.

Disease Exacerbations Associated with Changes in Oxygen Concentration, Air Pressure, and Humidity

At cruising altitude (approximately 11,500 m, or 37,000 feet), the aircraft cabin pressure is equivalent to the atmospheric pressure at approximately 1,500-2,500 m (5,000-8,000 ft) above sea level. Therefore, within the pressurized cabin, the inspired oxygen pressure is lower than the oxygen pressure at sea level. Most healthy travelers will not notice these changes. However, for travelers with cardiopulmonary diseases (especially those who normally require supplemental oxygen), cerebrovascular disease, anemia, and sickle cell disease, conditions in an aircraft can increase the risk of exacerbations of their underlying conditions.

People with chronic illnesses, particularly those whose conditions may be unstable, should be evaluated by a physician to ensure they are fit for travel. Those who require supplemental in-flight oxygen should notify the airline as far in advance as possible; at least 48 to 72 hours before departure. Information regarding what passengers can expect regarding the screening of respiratory equipment (e.g., oxygen canisters or Portable Oxygen Concentrators [POCs]) at airports in the United States and regulations regarding oxygen use on aircraft can be found at http://www.tsa.gov/travelers/airtravel/specialneeds/editorial_1370.shtm#6. Federal regulations prohibit airlines from allowing passengers to bring their own oxygen canisters aboard to use during the flight, and thus passengers must purchase them from the airline. Some airlines may offer oxygen only on certain types of air-craft, or they may limit the number of oxygen-requiring passengers per flight or per day; some airlines now allow only POCs. Travelers should also be aware that they are responsible for arranging their own oxygen supply while on the ground, at departure, during layovers, and on arrival. The National Home Oxygen Patients Association provides a brochure, Airline Travel with Oxygen, to assist patients who require supplemental oxygen during travel. The brochure is available through the website http://www.homeoxygen.org/airtrav.html.

Air in the middle ear and sinuses expands and contracts during ascent and descent to equalize with the cabin air pressure. People with ear, nose, and sinus infections or severe congestion may wish to avoid flying because the obstruction of air flow may cause pain and injury. This is particularly true for infants and toddlers, in whom obstruction occurs more readily because of the small diameter of the eustation tubes and sinus openings. The administration of oral pseudoephedrine 30 minutes before flight departure significantly reduced the occurrence of ear pain during flight in one study of adults with a history of recurrent ear pain associated with air travel (1). However, a similar study in children demonstrated no difference other than increased sleepiness (2). If flying cannot be postponed or avoided, anti-inflammatory agents (e.g., ibuprofen) may help reduce discomfort.

Abdominal gases also expand during flight, causing abdominal bloating and discomfort. Travelers who are particularly sensitive to these changes should avoid carbonated beverages and foods that can increase gas production. Furthermore, because of the potential damage that may result from gas expansion, patients who have had recent surgery, particularly intra-abdominal or intraocular procedures, should consult with their physicians before arranging air travel.

Aircraft cabin air is typically very dry, usually 10%-20% humidity. It is easy, therefore, to become dehydrated, and small children are especially susceptible. Passengers should try to limit consumption of alcoholic and caffeinated beverages, which can worsen dehydration. Instead, they should drink plenty of water before departure and during the flight. Travelers with underlying reactive airway disease (e.g., asthma) may also notice an increased reaction to the dry cabin air. Steroid-dependent asthmatics should consult their physicians about the potential need to increase steroid dosing during travel. Inhalers should be readily available in carry-on baggage to be used in the event of an exacerbation. Finally, some travelers may notice irritation from dryness of the skin, eyes, and airway passages. Moisturizers, saline eye drops (or rewetting drops for contact lenses), and saline nasal spray can alleviate these symptoms. Travelers should be advised to consult the Transportation Security Administration website prior to travel for current requirements regarding materials that may be brought on board in carry-on luggage (http://www.tsa.gov/travelers).

Ventilation and Air Quality

Older model airplanes provided 100% fresh air in the cabin. In an effort to conserve fuel, all commercial jet aircraft built after the late 1980s and a few modified older aircraft recirculate 10% to 50% of the air in the cabin mixed with outside air. The recirculated air passes through a series of filters 20-30 times per hour (3). In most newer model airplanes, the recycled air passes through high-efficiency particulate air (HEPA) filters, similar to those used in hospital respiratory isolation rooms, which capture 99.9% of particles (bacteria, fungi, and larger viruses) between 0.1 and 0.3 microns.(3)

In-Flight Transmission of Communicable Diseases

Concern has been increasing about the possible spread of communicable diseases during air travel. In certain circumstances when an infectious person or someone who is suspected of being infectious has traveled by air, public health authorities require passenger information for contact tracing and follow up. This information is collected from the passengers or the airlines and handled in a confidential manner. Information is available regarding in-flight transmission of a few diseases, including tuberculosis, Neisseria meningitidis, measles, influenza, SARS, and the common cold.

Tuberculosis

Only one investigation has documented transmission of Mycobacterium tuberculosis (TB) from a symptomatic passenger to six other passengers who were seated in the same section of a commercial aircraft during a long flight (>8 hours) (4). These six passengers were identified by conversion to a positive tuberculin skin test (TST); none had evidence of active tuberculosis. Driver et al. (5) investigated the potential for TB transmission by a symptomatic airline crew member over a 6-month period (5). They found that evidence of infection (i.e., TST positivity) among other crew members increased markedly during the period when the index case was most infectious and was associated with having worked >12 hours with the index case. Evidence suggested the potential that TB had been transmitted to passengers who had flown when the index case was most infectious.

The risk of TB transmission on commercial aircraft remains low (6). The number of air exchanges per hour in airplanes exceeds the number recommended for hospital isolation rooms. Contact investigations for persons exposed to TB during air travel are limited to situations in which the index case is believed to have been highly infectious (e.g., AFB smear-positive with cavitary or laryngeal TB) during travel AND when other passengers have had >8 hours of exposure to the index case, have taken more than one trip with the index case, or when ventilation on the aircraft has been restricted (7). Contact investigations are generally limited to passengers seated two rows in front and in back of the index case (4) and crew members serving the index case. People known to have infectious TB should travel by private transportation, rather than a commercial carrier, if travel is required.

Neisseria Meningitidis

Meningococcal disease has been documented in travelers, particularly those traveling for the Hajj; however, transmission due to exposure while aboard an aircraft has been documented very rarely. There is one report of two women who developed meningococcal infection after the same trans-Pacific flight with no direct personal contact, but it is unclear whether both travelers were exposed to a common source or whether the organism was transmitted from one passenger to the other (8). Antimicrobial prophylaxis should be considered for household members traveling with a patient, travel companions with close contact, other passengers who have had direct contact with respiratory secretions from the patient, and passengers seated directly next to the index patient on prolonged flights (≥8 hours). Guidelines for the management of airline passengers who have been exposed to meningococcal disease are available at http://wwwn.cdc.gov/travel/contentMenin.aspx.

Measles

Measles is a highly contagious viral disease. Most cases diagnosed in the United States are imported from countries where measles is still endemic (see Chapter 4). Furthermore, a person infected with measles is contagious from the first on-set of vague symptoms (up to 4 days before rash) to as long as 4 days after the development of rash; therefore, the potential for disease transmission during air travel is a concern. Despite this risk, very few cases of measles have been documented as a direct result of in-flight exposure. The in-flight exposure of passengers to a case of measles during a 7-hour flight from Japan to Hawaii resulted in no cases of fever and rash among those passengers responding to a post-exposure survey (9). This is likely explained by travelers’ high level of immunity to measles as a result of vaccination or previous exposure. Travelers should ensure they are immunized against measles prior to travel if they have not had the disease.

Influenza

Influenza is highly contagious, particularly among people in enclosed, poorly ventilated spaces. Transmission of influenza is thought to be primarily due to large droplets and has been documented aboard an aircraft, with most risk being associated with proximity to the source. (See Chapter 4 and http://www.cdc.gov/flu for more information.) The 1979 airplane-associated outbreak of influenza in Alaska, during which 72% of passengers became ill with influenza-like illness, does not reflect what generally happens on commercial flights. In this situation, the airplane experienced engine failure prior to takeoff and remained on the ground with the ventilation system turned off. The cabin doors remained closed, and many passengers remained on board for hours (10). In terms of understanding seasonal influenza transmission dynamics on a commercial airline, a potentially more useful influenza outbreak investigation associated with an aircraft is the 1999 outbreak reported in Australia, during which most of the infected passengers were seated within three rows of the index case, and all the people seated in the same row were infected (11).

Since 1997, a new strain of avian influenza virus (H5N1) has been shown to cause infection in humans, primarily associated with direct contact with birds and with no sustained human-to-human spread to date. Because influenza viruses are very adept at changing, there is concern that this strain could eventually to spread among humans and thus would impact air travel. See http://wwwn.cdc.gov/travel for more general information and up-to-date, specific guidelines for travelers and the airline industry.

SARS

SARS was first identified in Southern China in November 2002 and recognized as a global threat by March 2003. It is caused by a new coronavirus, the SARS-associated coronavirus (http://www.cdc.gov/ncidod/sars/factsheetcc.htm). During the 2002-2003 outbreak, more than 8000 persons became ill with 774 deaths in 26 countries on five continents (12). The last known case of person-to-person trans-mission of SARS in the world occurred in July 2003 (13). Were SARS to reemerge, http://wwwn.cdc.gov/travel will provide up-to-date information regarding the outbreak and the management of travel-related risk and guidelines for flight crews.

There was at least one well documented case of transmission of SARS on an aircraft (14). However, subsequent investigations failed to demonstrate that being in the air cabin environment increased the risk of transmission (15). SARS can potentially be transmitted anywhere people are gathered, including aircraft cabins. The probability of transmission is more likely to be determined by the infectiousness of the index patient rather than the physical setting. Thus, prevention efforts for air travel should continue to focus on reducing infectious particles on aircraft by discouraging persons who are acutely ill from traveling and reminding passengers to wash their hands frequently and cover their noses and mouths when coughing or sneezing.

Upper Respiratory Infections (The Common Cold)

The risk of transmission of upper respiratory infections (URI) on airplanes would seem high, given the close quarters passengers experience and the recirculation of air on most airplanes in operation. A study designed to evaluate the effect of recycled air (16) found that recirculated cabin air did not increase the risk for URI symptoms in passengers taking 2-hour flights on commercial jets. The rate of URI symptoms in these air travelers was consistent with that in other studies among people who were not traveling, suggesting that the increased risk of transmission of URIs on airplanes may be small, if present.

Disinsection

To reduce the international spread of mosquitoes and other vectors, a number of countries require disinsection of all in-bound flights. WHO and the International Civil Aviation Organization (ICAO) specify two approaches for aircraft disinsection: either spraying the aircraft cabin with an aerosolized insecticide (usually 2% phenothrin) while passengers are on board, or treating the aircraft’s interior surfaces with a residual insecticide while the aircraft is empty. Some countries use a third method, in which aircraft are sprayed with an aerosolized insecticide while passengers are not on board. Disinsection is currently not routinely done on incoming flights to the United States. Although disinsection, when done appropriately, was declared safe by the WHO in 1995, there is still much debate about the safety of the agents and methods used for disinsection. Although passengers and crew members have reported reactions to both the aerosols and residual insec-ticides, including rashes, respiratory irritation, burning eyes, and tingling and numbness of the lips and fingertips, there are no data to support a cause-and-effect relationship. Guidelines for disinsection have been updated for the revised International Health Regulations (http://www2a.cdc.gov/phlp/docs/58assembly.pdf PDF [272 KB/60 pages] see Annex 5). While only a few countries require disinsection for all in-bound flights, many countries, including the United States, reserve the right to increase the use of disinsection in the setting of increased threat of vector or disease spread. An updated list of countries that require disinsection and the types of methods used is available at the U.S. Department of Transportation website: (http://ostpxweb.dot.gov/policy/SafetyEnergyEnv/disinsection.htm).

Useful Links

• International Travel and Health. Travel by Air. International Travel and Health. WHO. Available at: http://www.who.int/ith

References

1. Csortan E, Jones J, Haan M, Brown M. Efficacy of pseudoephedrine for the prevention of barotrauma during air travel. Ann Emerg Med. 1994;23:1324-7.
2. Buchanan BJ, Hoagland J, Fischer PR. Pseudoephedrine and air travel-associated ear pain in children. Arch Pediatr Adolesc Med. 1999; 153:466-8.
3. National Academies. Subcommittee on Aviation. Hearing on the Aircraft Cabin Environment. June 5, 2003.  http://www.house.gov/transportation/aviation/06-05-03/06-05-03memo.html (accessed 11/22/06, link no longer available)
4. Kenyon TA, Valway SE, Ihle WW, Onorato IM, Castro KG. Transmission of multidrug-resistant Mycobacterium tuberculosis during a long airplane flight. N Engl J Med. 1996;334: 933-8.
5. Driver CR, Valway SE, Morgan WM, Onorato IM, Castro KG. Transmission of Mycobacterium tuberculosis associated with air travel. JAMA. 1994 Oct 5;272(13):1031-5.
6. World Health Organization. (1998). Tuberculosis and Air Travel: Guidelines for Prevention and Control. Available at http://www.who.int/tb/publications/2006/who_htm_tb_2006_363.pdf PDF (728 KB/47 pages) (accessed 11/10/06 and 11/21/06)
7. National Tuberculosis Controllers Association; Centers for Disease Control and Prevention. Guidelines for the investigation of contacts of persons with infectious tuberculosis. Recommendations from the National Tuberculosis Controllers Association and CDC. MMWR Morbid Mortal Wkly Recomm Rep. 2005 Dec 16;54(RR-15):1-47.
8. O’Connor BA, Chant KG, Binotto E, Maidment CA, Maywood P, McAnulty JM. Meningococcal disease—probable transmission during an international flight. Commun Dis Intell. 2005;29(3):312-4.
9. Amornkul P, Takahashi H, Bogard A, Nakata M, Harpaz R, Effler PV. Low risk of measles transmission after exposure on an international airline flight. J Infect Dis. 2004;189: S81-5.
10. Moser MR, Bender TR, Margolis HS, Noble GR, Kendal AP, Ritter DG. An outbreak of influenza aboard a commercial airliner. Am J Epidemiol. 1979;10:1-6.
11. Marsden AG. Influenza outbreak related to air travel. Med J Aust 2003;179:172-3.
12. Peiris JS, Yuen KY, Osterhaus AD, Stohr K. The severe acute respiratory syndrome. N Engl J Med. 2003;349:2431-41.
13. World Health Organization (2003). Consensus document on the epidemiology of severe acute respiratory syndrome (SARS) - 17 October 2003. Available at http://www.who.int/csr/sars/en/WHOconsensus.pdf PDF (795 KB/47 pages). (Accessed 04/14/06)
14. Wilder-Smith A, Paton N, Goh KT. Experience of severe acute respiratory syn-drome in Singapore: importation of cases, and defense strategies at the airport. J Travel Med. 2003;10:259-62.
15. Vogt TM, Guerra MA, Flagg EW, et.al. Risk of SARS-Associated Coronavirus Transmission Aboard Commercial Aircraft. J Travel Med. 2006;13:268-72.
16. Zitter, JN, Mazonson PD, Miller DP, Hulley SB, Balmes JR. Aircraft cabin air recirculation and symptoms of the common cold. JAMA. 2002 Jul 24-31;288:483-6.

WILLIAM R. MAC KENZIE, NANCY GALLAGHER