Measures to Prevent the Spread of Contagious Diseases by Air Transport
Jörg Siedenburg
Introduction
After a significant drop caused by the SARS-CoV-2 pandemic, air travel recovered and continues to be an important means for exchanging people and goods. More than 4 billion passengers are reported annually. However, contagious diseases can be spread by air traffic as well. Infected patients may use an aircraft and carry microbes to their destination or infect fellow passengers. Aircraft may carry unwanted passengers as well. Insect vectors as blind passengers may carry pathologic agents to the destinations of their vessels. The spread of Dengue Fever, Airport Malaria and Measles are examples.
Regulations on a national and international level, such as the International Health Regulations (IHR), have been implemented to prevent the spread of contagious diseases via international air traffic. The International Civil Aviation Organization (ICAO) has published guidelines for the disinsection of aircraft to preclude the carriage of arthropods.
Fig. 1: Schematic illustration of the ventilation of a large fuselage aircraft
AircraftsasaCarrierofInfectiousDiseases
At a cruising altitude of about 11.000 meters, the ambient pressure is about one-quarter compared to the sea level. A pressure cabin, using bleed air from the aircraft engine, creates a cabin pressure altitude of about 1.600 to 2.400 meters. The ensuing cabin pressure is about 25 % less than at sea level. Because outside air of less than -50 °C has to be heated to comfortable temperatures, the relative humidity of air is shallow. The subsequent physiological conditions on board (relative humidity between 5 and 15 %, 20–30 exchanges of cabin air, cleaning recirculation air with HEPA-(High-Efficiency Particulate Air) filters, laminar airflow in the cabin) make transmissions of infections very unlikely. The uniform forward orientation of passenger seats and little movement inside the cabin constitute more barriers to minimize the risk of transmission of contagious diseases within the aircraft cabin.
Nevertheless, air transport of infectious passengers is forbidden due to medical reasons, and IHR screening procedures prevent the boarding of contagious patients. Boarding, deboarding, and standing in line at check-in and baggage security controls pose a potential transmission hazard, which can be mitigated by additional measures like mouth-nose masks and face shields and keeping distance. During epidemics, often temperature screening before departure and/or after arrival can be implemented to identify infected passengers to deny boarding or isolating and observe them for a certain period to reduce the risk of importing a contagious disease.
During the ground time of scheduled flights, some arthropods may enter aircraft cabins, survive the flight time, and experience physiological conditions that are not arthropod-friendly. Assuming their remaining survival time matches the external incubation period of viruses or other parasites, it will be sufficient to recover from the stress of flight and have enough time to find susceptible humans at their destination to infect. It is very unlikely that all those pre-conditions are simultaneously suitable for a transmission match. Thus, a transmission is a rare event; however, given the many flights, such events happen regularly. There are a couple of reports of malaria transmission inside the aircraft or in the vicinity of airports where aircraft from malaria-endemic areas arrive. In addition, climate change and warmer temperatures in temperate climates make it easier for insects to thrive. Outbreaks of infectious diseases like Dengue Fever, Zika, West Nile Fever, etc., were formerly limited to tropical areas; therefore, the disinfection of aircraft before or during the flight is mandatory in certain countries for flights originating from tropical regions to minimize the risk of exporting them.
Fig. 2: At airports in the tropics not only passengers are boarding, insect vectors may enter as “blind passengers.
Disinsection of Aircraft
D-Phenothrin and Permethrin are used to disinsect aircraft. Both are so-called pyrethroids. Pyrethrum, a natural product from chrysanthemum flowers, was one of the first insecticides. Permethrin has a residual effect primarily on surfaces, affecting insects resting on those surfaces. d-Phenothrin has a small residual effect as well but acts primarily with significant “knockdown“ and “killing” effects on insects. Different methods certified by the ICAO (International Civil Aviation Organization) are recommended. A residual treatment method must be applied every eight weeks. Since 2023, three alternatives have been used.
- The pre-embarkation method is applied after cleaning the aircraft and catering, and after the cleaned surfaces have dried, 2 % d-Phenothrin as a fast-acting “knock-down”-insecticide is applied (35 g/100 m3).
- For the pre-departure method, d-Phenothrin in the same concentration is applied after cleaning and catering with the passengers seated and the overhead lockers still open.
- The on-arrival method is a contingency method and will be applied if the authorities at the destination are unsatisfied with the previous disinsection. It is applied before opening the doors of the aircraft.
Many airlines still use the so-called top-of-descent method or in-flight spraying (figure 3). D-Phenothrin is used as well. In each aisle a flight attendant has to walk slowly down the aisle and spray from two containers. The empty containers must be delivered to the health authorities. A standard announcement must announce each disinsection. The previous disinsection must be documented, and entry into the Declaration of Health must be mandatory.
Fig. 3: Top of descent disinsection with d-Phenothrin applied by the flight attendant from two bottles
Nevertheless, although all the different methods described minimize transmission of contagious diseases, the risk can never be reduced to zero. If clusters of exotic infections are found, quick diagnosis, thorough history, and measures to contain an initially small outbreak are required on a general level. A quick diagnosis can save the lives of those infected personally and potentially contact persons on a general level.
TransportofContagiousPatients
Air transport of contagious patients remains a big problem. When isolating a patient, who needs medical care, closed and open isolation are possible. In closed isolation, the patient is lying inside a container, and there is limited access for physicians and nurses from outside. Only minimal procedures can be performed. In open isolation, patients, doctors, and nurses are inside the same container, and complex procedures and logistics are possible. Both methods have been realized in air transport, using hypobaric pressure inside the containers. The latter prevents viral contamination from inside to outside. Small containers a little bit bigger than litter have been used in the French Forces for years. IsoArk® and EpiShuttle® are commercial solutions. However, these methods suit contagious diseases, not highly contagious diseases like hemorrhagic fevers.
Fig. 4: EpiShuttle® Isoltionstrage an Bord einer Pilatus P24 (Bild: Pilatus Aircraft Ltd, Schweiz)
The problem is a loss of cabin pressure. This is a rare event which might have catastrophic consequences for the transport of contagious patients. An aircraft leak would result in a sudden drop in cabin pressure; the container would explode. Viruses would spread in the form of aerosols and contaminate all persons on board and a vast area at a potential crash site. Therefore, countermeasures in case of a loss of cabin pressure are required to mitigate the risk. In 2014, an A 340 aircraft, the “Robert Koch,” was equipped accordingly for transporting German soldiers assisting in the Ebola virus outbreak in West Africa. It consisted of a tent-like container for patient and treatment, another one for doffing (get out of personal protection equipment [PPE]), and for donning (get into PPE) and stocks. All three were inter-connected and connected with an emergency pressure equilibration, basically a big plastic sack that would hold several hundred cubic meters of air in case of a loss of cabin pressure. The aircraft had never been used and was dismantled the following year. Should the need arise again, a copy of this make-shift model could not be repeated because many standards for aircraft construction, which also apply to equipment, would not allow for a simple copy.
Another aircraft used for transporting highly contagious patients was created under the aegis of the US CDC in the aftermath of the SARS epidemic in 2006. No construction details are published. Whether a loss of cabin pressure is being catered for is not clear.
In 2019, a project for a pan-European solution had been planned. The German Ministry of Foreign Affairs, Lufthansa Technik, Charité University Hospital in Berlin, and the EU were partners. It was based on a container solution consisting of three standard metal containers fitting to big transport aircraft and connected to a big plastic sack for pressure equilibration. These would have been stored in Berlin and fitted to any by any EU member. However, after significant planning and work had been done, the project was stopped for some reason.
For now, there would be no way to repatriate a highly contagious patient from overseas to Germany or any other European state. Another problem that would have to be addressed is that—different from scheduled air transport—state aircraft like the one we discuss would need a special permit to use the air space of all the countries overflown. The responses of several national aviation authorities to a request for air transportation of a patient with hemorrhagic fever can only be speculative.
References
- Siedenburg J: Luftverkehr und kontagiöse Erkrankungen. In: Siedenburg J, Küpper T (Hrsg.): Moderne Flugmedizin. Gentner-Verlag, Stuttgart 2015.
- Siedenburg J: Update kontagiöse Erkrankungen und internationaler Flugverkehr. FuR 2020; 27(3): 130–135. mehr lesen
- WHO (2023): WHO aircraft disinsection methods and procedures. , last access October 10, 2024. mehr lesen
Author
Captain (Navy MC Res) Dr. med. Jörg Siedenburg
Regional Medical Officer
German Embassy Nairobi
Kurstraße 36, 10117 Berlin
E-Mail: arzt-1@nair.auswaertiges-amt.de