Air Travel

Introduction

In 2019, 4.5 billion passengers took nearly 47 million international flights. The following year, annual global passenger air travel volume decreased by nearly two-thirds (1.8 billion passengers took 22 million flights), a consequence of the COVID-19 pandemic. The pandemic reversed a trend of annually increasing air travel volume, attributable at least in part to the implementation of travel restrictions by many countries. Since ending the global and U.S. public health emergency, global passenger air travel volume has reverted to pre-pandemic levels.

Travelers often have concerns about the health risks of flying on airplanes. Although illness might occur as a direct result of air travel, it is not commonly reported. Some main concerns include exacerbations of chronic medical conditions due to changes in air pressure and humidity; relative immobility during flights leading to thromboembolic disease (see Deep Vein Thrombosis and Pulmonary Embolism chapter); and risk for infection due to proximity to others on board who could have communicable diseases.

Pre-flight medical considerations

The Aerospace Medical Association recommends evaluating chronic medical conditions and addressing instabilities prior to travel, particularly in people with underlying cardiovascular disease, diabetes, chronic lung disease, mental illness, seizures, stroke, recent surgery, or a history of deep vein thrombosis or pulmonary embolism. Travelers should be current on routine vaccinations and receive destination-specific vaccinations before travel to protect themselves and their contacts (see Travelers with Chronic Illnesses chapter for additional information on the overall impact of air travel on chronic medical conditions).

Pregnant travelers and children

For information on contraindications and precautions related to flying during pregnancy, see Pregnant Travelers chapter. For information on how to keep children safe during travel, including recommendations for safety on an airplane, see Traveling Safely with Infants and Children chapter.

Travelers with disabilities

The U.S. Transportation Security Administration has information for travelers with disabilities and medical conditions that might affect their security screening. Travelers with Disabilities chapter, includes a table of useful online resources (Table 2.3.1). For information on traveling with a service animal, see Traveling with Pets and Service Animals.

Travelers who require supplemental oxygen

Travelers who require supplemental in-flight oxygen should be aware that they must arrange for their own oxygen supplies while on the ground, at departure, during layovers, and upon arrival. Federal regulations prohibit passengers from bringing their own oxygen onboard flights; passengers should notify the airline ≥72 hours before departure if they require in-flight supplemental oxygen. In addition, airlines might not offer in-flight supplemental oxygen on all aircraft or flights, and some airlines permit only Federal Aviation Administration (FAA)-approved portable oxygen concentrators. See information about screening portable oxygen concentrators at U.S. airports.

Cabin air pressure and chronic disease

During normal flight conditions, FAA requires that commercial aircraft maintain a cabin pressure equivalent to a maximum altitude of 2,440 m (approximately 8,000 ft) above sea level. Cabin pressures are typically maintained at an equivalent of 1,830–2,440 m (approximately 6,000–8,000 ft) above sea level, but newer aircraft can maintain cabin air pressures equivalent to lower altitudes. Most travelers who reside in altitudes below 1,830–2,440 m (6,000–8,000 ft) and without preexisting health conditions will not notice any effects from the decreased partial pressure of oxygen at these cabin pressures. By contrast, a traveler with anemia (including sickle cell disease), cardiopulmonary disease (especially people who normally require supplemental oxygen), or cerebrovascular disease can experience an exacerbation of their underlying medical condition. In addition, aircraft cabin air is typically dry, usually 10%–20% humidity, which can cause dryness of the mucous membranes of the upper airway and eyes.

Barotrauma

Barotrauma can occur when the pressure inside an air-filled, enclosed body space (e.g., abdomen, middle ear, sinuses) is not the same as the air pressure inside the aircraft cabin. Barotrauma most commonly occurs because of rapid changes in environmental pressure: during ascent, for example, when cabin pressure falls rapidly, and during descent, when cabin pressure quickly rises. Barotrauma most commonly affects the middle ear and happens when the eustachian tube is blocked and a traveler is unable to equalize the air pressure in the middle ear with the outside cabin pressure.

Middle ear barotrauma is usually not severe or dangerous; rarely, though, it can cause complications (e.g., dizziness, hearing loss, a perforated tympanic membrane, permanent tinnitus). To help reduce the risks of barotrauma associated with cabin air pressure changes, travelers with ear, nose, and sinus infections or severe congestion might choose to postpone flying to prevent pain or injury or use oral or nasal decongestants to help alleviate symptoms. Travelers with allergies should continue their regular allergy medications.

Travelers who have had recent surgery, particularly intra-abdominal, cardiothoracic, or intraocular procedures, should consult with their physician before flying. Travelers who participate in scuba diving should observe minimum recommended time intervals between diving and air travel to reduce the risk for altitude-induced decompression sickness (see Scuba Diving: Decompression Illness and Other Dive-Related Injuries chapter).

Transmission of communicable disease during air travel

Communicable diseases can be transmitted during air travel. For example, otherwise healthy adults can transmit influenza virus to others for 5–7 days after symptom onset. Transmission of other respiratory viruses (e.g., measles) has also been documented on commercial aircraft. However, it is difficult to quantify the risk of transmission onboard an aircraft due to other potential exposures in community settings (including airports) or households.

Some pathogens, such as influenza virus or respiratory syncytial virus, can be spread through exposure to infectious droplets (e.g., when an ill person sneezes or coughs and the secretions or droplets land on another person's face, mouth, nose, or eyes), direct contact with an infected person, or indirect contact when an infected person touches communal surfaces (e.g., door handles, restroom faucets) with contaminated hands. Other pathogens, such as SARS-CoV-2, measles virus, and Mycobacterium tuberculosis, can be spread by smaller particles or aerosols, such as droplet nuclei, that can remain airborne for prolonged periods of time.

Although there have been no studies specific to air travel, nonpharmaceutical interventions, such as masking, hand and respiratory hygiene, and physical distancing, are likely to be effective in mitigating transmission in the airport, in the jet bridge, and on an aircraft. Travelers should wash their hands frequently and thoroughly or use an alcohol-based hand sanitizer containing ≥60% alcohol, especially after using the restroom, after coughing or sneezing, and before eating meals. Practicing good handwashing and respiratory hygiene (e.g., covering your mouth with a tissue when coughing or sneezing) can help decrease the risk of infection by direct or indirect contact. In addition, wearing a high-quality and well-fitting mask or respirator (such as an N95 filtering facepiece respirator) can be effective in reducing transmission of respiratory pathogens, especially when combined with hand hygiene. To minimize exposure to communicable diseases, passengers should try to avoid touching potentially contaminated surfaces (e.g., aircraft seat backs) and consider wearing high-quality and well-fitting masks or respirators, especially during boarding and deplaning, when the risk of transmission is highest.

Cabin ventilation and air filtration

Large commercial jet aircraft recirculate 35%–55% of the air in the cabin, mixed with outside air. The recirculated air passes through high-efficiency particulate air (HEPA) filters that capture 99.97% of particles (e.g., bacteria, viruses, fungi) ≥0.3 µm in diameter. Furthermore, airflow generally circulates in defined areas within the aircraft, thus limiting the radius of distribution of pathogens spread by small-particle aerosols. Cabin air is refreshed 20–30 times an hour, much higher than the air exchange rate in most office buildings. As a result, the cabin air environment is less conducive to the spread of most infectious diseases than typical environmental systems in buildings. However, while high air exchanges make airborne transmission of infection less likely, the close proximity of passengers increases the risk of person-to-person airborne spread before contaminated air can be removed from the breathing zone and exhausted or filtered. There is also a concern for airborne transmission when the aircraft's ventilation system is off, as occurs during de-icing, runway delays, boarding, deplaning, and so on.

Acute respiratory illnesses and air travel

SARS-CoV-2 transmission during air travel has been documented. In general, SARS-CoV-2 transmission risk on aircraft remains difficult to quantify and is likely to be affected by evolving engineering, administrative, and other controls (including personal protective equipment) being widely implemented in the commercial air travel sector. In 2020, U.S. government agencies and the International Civil Aviation Organization each developed guidance for the airline industry to use in response to the pandemic that may continue to be relevant in the post-pandemic period. Recommendations included maximizing total cabin airflow on commercial aircraft during both ground and flight operations; implementing surface decontamination measures aimed at reducing risk for contact with infectious droplets; and modifying passenger movement patterns before, during, and after travel. Combining other mitigation measures, such as mask-wearing and cleaning of frequently touched surfaces, with the aircraft air filtration systems results in a low risk of SARS-CoV-2 transmission in the aircraft cabin.

Travelers should familiarize themselves with the latest recommendations for acute respiratory illnesses (e.g., COVID-19, influenza, and respiratory syncytial virus infection) when planning air travel and, as their departure date approaches, follow the guidance of corresponding health authorities. People who have respiratory symptoms should consider testing prior to departure. People with confirmed or suspected acute respiratory infections should delay travel until they are no longer thought to be contagious. Those exposed to a person with COVID-19 should consider testing prior to departure and take additional precautions, according to current guidance.

Aircraft disinsection

In 2003, there was an increase in the number of cases of malaria infection among individuals without recent travel to an endemic region. In rare cases, these infections may be due to aircraft-imported insect vectors if the aircraft had been operating in a malaria-endemic setting. Under the International Health Regulations published after the Zika outbreaks in 2015–2016, prior to departure, airlines are recommended to disinsect aircraft departing a region with high rates of vector-borne diseases. However, while the efficacy of aircraft disinsection has been observed in trials, there is limited evidence of the effectiveness of using insecticide to kill mosquitoes inside aircraft cabins to prevent the introduction and spread of mosquito-borne diseases during flight operations.

In-flight medical emergencies

Under the Aviation Medical Assistance Act of 1998, the FAA mandates airlines to maintain specific medical supplies onboard aircraft and flight attendants to be trained in basic first aid procedures (e.g., cardiopulmonary resuscitation, use of an automated external defibrillator). The goal of managing in-flight emergencies is to stabilize the passenger until the flight can safely reach ground-based medical care (for additional information, see Perspectives: Responding to Medical Emergencies When Flying chapter).

Regulatory authorities to prevent illness before, during, and after travel

The Centers for Disease Control and Prevention (CDC) has statutory authority to publish regulations to prevent the introduction, transmission, and spread of communicable diseases from foreign countries into and within U.S. states and territories. CDC may issue federal public health orders for quarantine, isolation, or conditional release for certain communicable diseases that are designated as quarantinable by the president of the United States through executive order. Diseases falling under this specific federal public health authority are listed in Box 7.1.1. The list of federally quarantinable diseases can be revised by executive order when a communicable disease becomes a significant public health threat. For more information, see Specific Laws and Regulations Governing the Control of Communicable Diseases.

Many of CDC's public health actions before, during, and after flights to prevent or mitigate the introduction and spread of diseases of public health concern are carried out by CDC port health station personnel working in collaboration with state, tribal, local, and territorial public health officers. CDC port health stations are located at the 20 ports of entry, including land border crossings, where most travelers arrive to or transit through the United States. See more information on CDC port health stations.

Box 7.1.1

Travel restrictions

Under the authority of the Aviation and Transportation Security Act (49 USC 114), CDC and the U.S. Department of Homeland Security (DHS) developed a public health Do Not Board (DNB) list to prevent people from boarding commercial aircraft if they are known to have, are suspected of having, or were exposed to a communicable disease of public health concern with risk of transmission during air travel. A person placed on the DNB list will not be issued a boarding pass for any commercial airline flight originating from or arriving at a U.S. airport. The Public Health Lookout (PHLO) complements the DNB list to notify DHS U.S. Customs and Border Protection officers at sea, land, and air borders of a person's infectious disease status that may need public health intervention. For more information about the DNB/PHLO lists, see FAQs for Public Health Do Not Board and Lookout Lists.

Reporting requirements for aircrafts

Federal regulations mandate that the commander of an aircraft must report, before arrival to a U.S. port of entry, any death or "ill person" among passengers or crew aboard the aircraft to the CDC port health station with jurisdiction for the arrival airport. For the definition of an ill person, see CFR Title 42 §71.21: Report of death or illness (Box 7.1.2). CDC additionally receives notifications of illness or death occurring during or after travel from Customs and Border Protection officers, emergency medical personnel, and state, tribal, local, and territorial health departments. CDC provides guidance to airlines on reporting and managing ill travelers on airlines here: Managing Ill Passengers/Crew. See Cruise Ship Travel chapter on similar reporting requirements for maritime vessels.

Box 7.1.2

Notes

¹Definition applies to all travelers, including passengers and crew, U.S. citizens and non-U.S. citizens.

²Measured temperature ≥38°C (≥100.4°F); feels warm to the touch; or provides a history of feeling feverish.

Illness response

CDC's goals in responding to reports of illness concerning travelers are to determine whether the illness poses (or has the potential to pose) a public health threat and to take appropriate public health actions. After an ill traveler has been reported to CDC and the flight has landed, public health officials can either allow ill travelers to resume travel if their illness does not pose a meaningful public health risk; recommend that ill travelers with a suspected communicable disease seek medical care and delay further commercial travel until noninfectious; or require ill travelers to be medically evaluated if they are suspected of having a quarantinable communicable disease.

Together with airport and public health response partners (e.g., emergency medical services, public health authorities), CDC staff conduct public health assessments of ill travelers and make recommendations regarding potentially exposed travelers. Potentially exposed travelers might be asked to provide their contact information before disembarking so that health authorities can follow up and provide additional health information if the ill traveler is diagnosed with a disease of public health concern.

Acknowledgements

The following authors contributed to the previous version of this chapter: Tai-Ho Chen and Araceli Rey.