Air Travel

For most healthy persons, air travel may be more cumbersome than in the past but should not pose any specific health risks. However, for travellers with underlying medical problems, conditions in an aircraft can increase the risk of a number of health-related problems. At cruising altitude (approximately 11,500m, or 37,000 feet), the aircraft cabin pressure is equivalent to the atmospheric pressure at approximately 1,500-2,500m (5,000-8,000ft) above sea level. Therefore, within the pressurized cabin, the inspired oxygen pressure is lower than the oxygen pressure at sea level. Most healthy travellers will not notice these changes. However, passengers with cardiopulmonary diseases (especially those who normally require supplemental oxygen), cerebrovascular disease, anaemia, and sickle cell disease may suffer from signs or symptoms related to exacerbations of their underlying conditions.

People with chronic illnesses, particularly those whose conditions may be unstable, should have a pre-travel examination 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 hours before departure. Not all airlines provide in-flight supplemental oxygen. Furthermore, some airlines offer oxygen only on certain types of aircraft, or they may limit the number of oxygen-requiring passengers per flight or per day. Travellers should also be aware that they are responsible for arranging their own oxygen supply while on the ground, both at departure and on arrival. Passengers should make arrangements with their oxygen supplier as soon as possible to have a representative meet them at the airport. The National Home Oxygen Patients Association (www.homeoxygen.org) provides a brochure, Airline Travel with Oxygen, to assist patients who require supplement oxygen during travel. They also provide a list of specific requirements and prices for individual airlines. The brochure and list are available through the website.

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 should avoid flying because the obstruction of air flow may cause pain and injury. If flying cannot be postponed or avoided, decongestants and anti-inflammatory agents may help reduce air flow obstruction and discomfort. Abdominal gases also expand during flight, causing abdominal bloating and discomfort. Travellers 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. Travellers with underlying reactive airway disease (e.g., asthma) may also notice 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 travellers may notice irritation due to 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.

Immobility coupled with long flights increases the risk of venous stasis and the formation of blood clots (deep vein thrombosis or DVT) in the legs. Although most people with DVT have mild or no symptoms, severe pulmonary emboli have been reported in passengers up to several days after travel. People at increased risk for DVT include those who have had DVT in the past, have undergone recent surgery (especially abdominal or orthopaedic surgery), are pregnant, have a malignancy, or have genetic blood-clotting abnormalities. People with such conditions should consult with a physician before travelling. However, travellers should be aware that DVT can occur in people without known risk factors. Measures to combat stasis include ensuring adequate hydration, wearing compression stockings and loose-fitting clothing, periodically walking through the cabin, and stretching. Occasionally, people who are at higher risk are advised to use an anticoagulant medication, such as aspirin or low molecular-weight heparins.

For the most part, the quality of air in the cabin should not pose a hazard for travellers. Commercial aircraft are equipped with environmental control systems that monitor and control pressurization, air flow, air filtration, and temperature. Older model airplanes provide 100% fresh air in the cabin, while newer models, in an effort to conserve fuel, provide up to 50% recycled air in the cabin. The recycled air passes through filters, typically high-efficiency particulate air (HEPA) filters, similar to those used in hospital respiratory isolation rooms. Moreover, the air in the cabin is recirculated 20-30 times per hour (approximately one cycle every 3 minutes). The recycled air has not been found to adversely affect air quality in the cabin.

In-Flight Disease Transmission

Concern has been increasing about the possible spread of communicable diseases during air travel. Infections of particular concern include tuberculosis, Neisseria meningitidis, measles, influenza, and SARS.

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). These six passengers were identified by conversion to a positive tuberculin skin test; none had evidence of active tuberculosis. The HEPA filters used in newer commercial aircraft (described above) are able to filter out TB bacteria from the recycled air and are used in hospital respiratory isolation rooms to prevent the spread of TB within the hospital setting. Furthermore, the number of air exchanges per hour in airplanes exceeds the number recommended for hospital isolation rooms. The risk of TB transmission on commercial aircraft, therefore, remains low. People known to have infectious TB should travel by private transportation, rather than a commercial carrier, if travel is required. See CDC web site for more information (http://www.cdc.gov/travel/tb_risk.htm).

Neisseria meningitidis

Meningococcal disease has been documented in travellers, particularly those travelling for the Hajj; however, transmission due to exposure while aboard an aircraft has not been documented. Guidelines for the management of airline passengers who have been exposed to meningococcal disease are available at http://www.cdc.gov/travel/menin-guidelines.htm.

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 Measles section). Furthermore, a person infected with measles is contagious from the first onset of vague symptoms (up to 4 days before rash) to approximately 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. Travellers should ensure they are immunised if they have not had the disease.

Influenza

Influenza is highly contagious, particularly among people in enclosed spaces. Transmission of infection has been documented aboard an aircraft, with most risk being associated with proximity to source. (See Influenza section and http://www.cdc.gov/flu for more information.) Since December 2003, a new strain of avian influenza virus has been shown to cause infection in humans, with limited human-to-human spread. Because influenza viruses are very adept at changing, there is concern that this strain could eventually become a threat and thus affect air travel. See the CDC Avian Flu website for more general information and guidelines (http://www.cdc.gov/flu/avian/index.htm).

SARS

SARS was first identified in Southern China in November 2002 and recognised 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). Despite the clear role of international travel in the spread of SARS during the 2003 outbreak, only one case of in-flight transmission has been confirmed. The CDC SARS web site (http://www.cdc.gov/ncidod/sars/index.htm) has up-to-date information regarding the management of travel-related risk and guidelines for flight crews.

From investigations of disease outbreaks associated with air travel, two main risk factors for the spread of communicable diseases have been identified: flight duration (greater than or equal to8 hours, including ground time) and seating proximity to the source. There is also increased risk of spread when the aircraft ventilation system is off. (In general, the environmental systems are on when the engines are on or when an auxillary unit is used, such as when the aircraft is on the ground at the gate.) To reduce the spread of disease, standard respiratory and hand hygiene practices should always be encouraged. People with febrile illnesses or other possible communicable diseases should postpone air travel. Furthermore, airline regulations require that passengers be removed from an aircraft within 30 minutes of shutting off the ventilation system.

Disinsection

Disinsection = spraying aircraft for insects.

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 spray the aircraft cabin with an aerosolized insecticide (usually 2% phenothrin) while passengers are on board, or treat 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. 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 insecticides, 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 are being updated for the revised International Health Regulations. While only a few countries require disinsection for all in-bound flights, many countries 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 are available at the U.S. Department of Transportation website: (http://ostpxweb.dot.gov/policy/Safety%20Energy%20Env/disinsection.htm).

Useful Links

  • International Travel and Health. Travel by Air. International Travel and Health. WHO. Available at: http://www.who.int/ith
  • Aerospace Medical Association. Useful Tips for Airline Travel. Available at http://www.asma.org/Publication/Tips_For_Travellers2001.pdf
  • Transportation Security Administration (TSA) website: http://www.tsa.gov/public/interapp/editorial/editorial_1568.xml
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- Phyllis Kozarsky and Deborah Nicolls

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