Travel by air and by sea exposes passengers to a number of factors that may have
an impact on health. In this chapter, technical terms have been used sparingly
in order to facilitate use by a wide readership. Medical professionals needing
more detailed information are referred to the web site of the Aerospace Medical
Association (http://www.asma.org) and the web site of the International Maritime
Health Association (http://www.imha.net/).
2.1 Travel by air
The volume of air traffic has continued to rise over the years and “frequent flyers”
now make up a substantial proportion of the travelling public. The number of
long-haul flights has increased. According to the International Civil Aviation
Organization, passenger traffic is projected to double between 2006 and 2020.
Air travel, particularly over long distances, exposes passengers to a number of
factors that may have an effect on their health and well-being. Travellers with
pre-existing health problems and those receiving medical care are more likely to
be affected and should consult their doctor or a travel medicine clinic in good
time before travelling. Health risks associated with air travel can be minimized if
the traveller plans carefully and takes some simple precautions before, during and
after the flight. An explanation of the various factors that may affect the health
and well-being of air travellers follows.
2.1.1 Cabin air pressure
Although aircraft cabins are pressurized, cabin air pressure at cruising altitude
is lower than air pressure at sea level. At typical cruising altitudes in the range
11 000–12 200 m (36 000–40 000 feet), air pressure in the cabin is equivalent to
the outside air pressure at 1800–2400 m (6000–8000 feet) above sea level. As a
consequence, less oxygen is taken up by the blood (hypoxia) and gases within the
body expand. The effects of reduced cabin air pressure are usually well tolerated
by healthy passengers.
Oxygen and hypoxia
Cabin air contains ample oxygen for healthy passengers and crew. However,
because cabin air pressure is relatively low, the amount of oxygen carried in the
blood is reduced compared with that at sea level. Passengers with certain medi-
cal conditions, particularly heart and lung diseases and blood disorders such as
anaemia (in particular sickle-cell anaemia), may not tolerate this reduced oxygen
level (hypoxia) very well. Some of these passengers are able to travel safely if ar-
rangements are made with the airline for the provision of an additional oxygen
supply during flight. However, because regulations and practices differ from
country to country and between airlines, it is strongly recommended that these
travellers, especially those wishing to carry their own oxygen, contact the airline
early in their travel plans. An additional charge is often levied on passengers who
require supplemental oxygen to be provided by the airline.
Gas expansion
As the aircraft climbs in altitude after take-off, the decreasing cabin air pressure
causes gases to expand. Similarly, as the aircraft descends in altitude before landing,
the increasing pressure in the cabin causes gases to contract. These changes may
have effects where air is trapped in the body.
Passengers often experience a “popping” sensation in the ears caused by air es-
caping from the middle ear and the sinuses during the aircraft’s climb. This is not
usually considered a problem. As the aircraft descends in altitude prior to landing,
air must flow back into the middle ear and sinuses in order to equalize pressure.
If this does not happen, the ears or sinuses may feel as if they are blocked and
pain can result. Swallowing, chewing or yawning (“clearing the ears”) will usu-
ally relieve any discomfort. As soon as it is recognized that the problem will not
resolve itself using these methods, a short forceful expiration against a pinched
nose and closed mouth (Valsalva manoeuvre) should be tried and will usually
help. For infants, feeding or giving a pacifier (dummy) to stimulate swallowing
may reduce the symptoms.
Individuals with ear, nose and sinus infections should avoid flying because pain
and injury may result from the inability to equalize pressure differences. If travel
cannot be avoided, the use of decongestant nasal drops shortly before the flight
and again before descent may be helpful.
As the aircraft climbs, expansion of gas in the abdomen can cause discomfort,
although this is usually mild.
Some forms of surgery (e.g. abdominal surgery) and other medical treatments or
tests (e.g. treatment for a detached retina) may introduce air or other gases into a
body cavity. Travellers who have recently undergone such procedures should ask
a travel medicine physician or their treating physician how long they should wait
before undertaking air travel.
2.1.2 Cabin humidity and dehydration
The humidity in aircraft cabins is low, usually less than 20% (humidity in the home
is normally over 30%). Low humidity may cause skin dryness and discomfort to
the eyes, mouth and nose but presents no risk to health. Use skin moisturizing
lotion or a saline nasal spray to moisturize the nasal passages. Wearing eyeglasses
rather than contact lenses can relieve or prevent discomfort to the eyes. The avail-
able evidence has not shown low humidity to cause internal dehydration and there
is no need to drink more than usual. However, since caffeine and alcohol have a
diuretic effect (causing more urine to be produced), it is wise to limit consumption
of such beverages during long flights.
2.1.3 Ozone
Ozone is a form of oxygen that occurs in the upper atmosphere and may enter
the aircraft cabin together with the fresh-air supply. In older aircraft, it was found
that the levels of ozone in cabin air could sometimes lead to irritation of the lungs,
eyes and nasal tissues. Ozone is broken down by heat and a significant amount of
ozone is removed by the engine compressors (which compress and heat the air)
that provide pressurized air for the cabin. In addition, most modern long-haul
jet aircraft are fitted with equipment (catalytic converters) that breaks down any
remaining ozone.
2.1.4 Cosmic radiation
Cosmic radiation is made up of radiation that comes from the sun and from outer
space. The Earth’s atmosphere and magnetic field are natural shields and cosmic
radiation levels are therefore lower at lower altitudes. The Earth’s population is
continually exposed to natural background radiation from soil, rock and building
materials as well as from cosmic radiation that reaches the Earth’s surface.
Cosmic radiation is more intense over polar regions than over the equator because
of the shape of the Earth’s magnetic field and the “flattening” of the atmosphere
over the poles. Although cosmic radiation levels are higher at aircraft cruising
altitudes than at sea level, research has not shown any significant health effects
for aircraft passengers or crew.
Environmental health risks
Travellers often experience abrupt and dramatic changes in environmental condi-
tions, which may have detrimental effects on health and well-being. Travel may
involve major changes in altitude, temperature and humidity, and exposure to
microbes, animals and insects. The negative impact of sudden changes in the
environment can be minimized by taking simple precautions.
3.1 Altitude
Barometric pressure falls with increasing altitude, diminishing the partial pressure
of oxygen and causing hypoxia. The partial pressure of oxygen at 2500 m, the
altitude of Vail, Colorado, for example, is 26% lower than at sea level; in La Paz,
Plurinational State of Bolivia (4000 m), it is 41% lower. This places a substantial
stress on the body, which requires at least a few days to acclimatize; the extent
of acclimatization may be limited by certain medical conditions, especially lung
disease. An increase in alveolar oxygen through increased ventilation is the key to
acclimatization; this process starts at 1500 m. Despite successful acclimatization,
aerobic exertion remains difficult and travellers may still experience problems
with sleep.
High-altitude illness (HAI) results when hypoxic stress outstrips acclimatization.
HAI can occur at any altitude above 2100 m but is particularly common above
2750 m. In Colorado ski resorts, incidence of HAI varies from 15% to 40%, de-
pending on sleeping altitude. Susceptibility is primarily genetic, but fast rates of
ascent and higher sleeping altitudes are important precipitating factors. Age, sex
and physical fitness have little influence.
The spectrum of HAI includes common acute mountain sickness (AMS), occasional
high-altitude pulmonary oedema and, rarely, high altitude cerebral oedema. The
latter two conditions, although uncommon, are potentially fatal. AMS may occur
after 1–12 h at high altitude. Headache is followed by anorexia, nausea, insomnia,
fatigue and lassitude. Symptoms usually resolve spontaneously in 24–48 h and are
ameliorated by oxygen or analgesics and antiemetics. Acetazolamide, 5 mg/kg per day in divided doses, is an effective chemoprophylaxis for all HAI; it is started
one day before travel to altitude and continued for the first 2 days at altitude.
Acetazolamide should not be given to individuals with history of allergy to sul-
fonamide drugs.
Only a few conditions are contraindications for travel to altitude; they include
unstable angina, pulmonary hypertension, severe chronic obstructive pulmonary
disease (COPD) and sickle-cell anaemia. Patients with stable coronary disease,
hypertension, diabetes, asthma or mild COPD and pregnant women generally
tolerate altitude well but may require monitoring of their condition. Portable and
stationary oxygen supplies are readily available in most high-altitude resorts and –
by removing hypoxic stress – remove any potential danger from altitude exposure.
Precautions for travellers unaccustomed to high altitudes
● Avoid one-day travel to sleeping altitudes over 2750 m if possible. Break the
journey for at least one night at 2000–2500 m to help prevent AMS.
● Avoid overexertion and alcohol for the first 24 h at altitude; drink extra water.
● If direct travel to sleeping altitude over 2750 m is unavoidable, consider pro-
phylaxis with acetazolamide. Acetazolamide is also effective if started early in
the course of AMS.
● Travellers planning to climb or trek at high altitude will require a period of
gradual acclimatization.
● Travellers with pre-existing cardiovascular or pulmonary disease should seek
medical advice before travelling to high altitudes.
● Travellers with the following symptoms should seek medical attention when
experiencing, at altitude:
— symptoms of AMS that are severe or last longer than 2 days;
— progressive shortness of breath with cough and fatigue;
— ataxia or altered mental status.
3.2 Heat and humidity
Sudden changes in temperature and humidity may have adverse effects on health.
Exposure to high temperature results in loss of water and electrolytes (salts) and
may lead to heat exhaustion and heat stroke. In hot dry conditions, dehydration is
particularly likely to develop unless care is taken to maintain adequate fluid intake.
The addition of a little table salt to food or drink (unless this is contraindicated for the individual) can help to prevent heat exhaustion, particularly during the
period of adaptation.
Consumption of salt-containing food and drink helps to replenish the electrolytes
in case of heat exhaustion and after excessive sweating. Travellers should drink
enough fluid to be able to maintain usual urine production; older travellers should
take particular care to consume extra fluids in hot conditions, as the thirst reflex
diminishes with age. Care should be taken to ensure that infants and young children
drink enough liquid to avoid dehydration.
Irritation of the skin may be experienced in hot conditions (prickly heat). Fungal
skin infections such as tinea pedis (athlete’s foot) are often aggravated by heat and
humidity. A daily shower using soap, wearing loose cotton clothing and applying
talcum powder to sensitive skin areas help to reduce the development or spread
of these infections.
Exposure to hot, dry, dusty air may lead to irritation and infection of the
eyes and respiratory tract. Avoid contact lenses in order to reduce the risk of
eye problems.
AMOEBIASIS
Cause Caused by the protozoan parasite Entamoeba histolytica.
Transmission Transmission occurs via the faecal–oral route, either directly by person-to-
person contact or indirectly by eating or drinking faecally contaminated food
or water.
Nature of disease The clinical spectrum ranges from asymptomatic infection, diarrhoea and dysen-
tery to fulminant colitis and peritonitis as well as extraintestinal amoebiasis.
Acute amoebiasis can present as diarrhoea or dysentery with frequent,
small and often bloody stools. Chronic amoebia sis can present with
gastrointestinal symptoms plus fatigue, weight loss and occasional fever.
Extraintestinal amoebiasis can occur if the parasite spreads to other
organs, most commonly the liver where it causes amoebic liver abscess.
Amoebic liver abscess presents with fever and right upper quadrant
abdominal pain.
Geographical distribution Occurs worldwide, but is more common in areas or countries with poor
sanitation, particularly in the tropics.
Precautions Food and water hygiene (Chapter 3). No vaccine is available.
ANGIOSTRONGYLIASIS
Cause Caused by Angiostrongylus cantonensis, a nematode parasite.
Transmission Transmission occurs by ingestion of third-stage larvae in raw or undercoo-
ked snails or slugs. It can also result from ingestion of raw or undercooked
transport hosts such as freshwater shrimp or prawns, crabs and frogs.
Nature of disease Ingested larvae can migrate to the central nervous system and cause eosi-
nophilic meningitis.
Geographical distribution Occurs predominantly in Asia and the Pacific, but has also been reported in
the Caribbean. Geographical expansion may be facilitated by infected ship-
borne rats and the diversity of snail species that can serve as intermediate
hosts.
Precautions Food and water hygiene (Chapter 3); in particular avoid eating raw/under-
cooked snails and slugs, or raw produce such as lettuce. No vaccine is
available.
ANTHRAX
Cause Bacillus anthracis bacteria.
Transmission Anthrax is primarily a disease of animals. Cutaneous infection, the most
frequent clinical form of anthrax, occurs through contact with products from
infected animals (mainly cattle, goats, sheep), such as leather or woollen
goods, or through contact with soil containing anthrax spores.
Nature of the disease A disease of herbivorous animals that occasionally causes acute infection
in humans, usually involving the skin, as a result of contact with contami-
nated tissues or products from infected animals or with anthrax spores in
soil. Untreated infections may spread to regional lymph nodes and to the
bloodstream, and may be fatal.
Geographical distribution Sporadic cases occur in animals worldwide; there are occasional outbreaks
in Africa and central Asia.
Risk for travellers Very low for most travellers.
Prophylaxis None. (A vaccine is available for people at high risk because of occupational
exposure to B. anthracis; it is not commercially available in most countries.)
Precautions Avoid direct contact with soil and with products of animal origin, such as
souvenirs made from animal skins.
BRUCELLOSIS
Cause Several species of Brucella bacteria.
Transmission Brucellosis is primarily a disease of animals. Infection in people is acquired
from cattle (Brucella abortus), dogs (B. canis), pigs (B. suis), or sheep and
goats (B. melitensis), usually by direct contact with infected animals or by
consumption of unpasteurized (raw) milk or cheese.
Nature of the disease A generalized infection with insidious onset, causing continuous or intermit-
tent fever and malaise, which may last for months if not treated adequately.
Relapse is not uncommon after treatment.
Geographical distribution Worldwide, in animals. It is most common in developing countries, South
America, central Asia, the Mediterranean and the Middle East.
Risk for travellers Low for most travellers. Those visiting rural and agricultural areas in countries
or areas at risk may be at greater risk. There is also a risk in places where
unpasteurized milk products are sold near tourist centres.
Prophylaxis None.
Precautions Avoid consumption of unpasteurized milk and milk products and direct
contact with animals, particularly cattle, goats and sheep.
CHIKUNGUNYA
Cause Chikungunya virus – an Alphavirus (family Togaviridae).
Transmission Chikungunya is a viral disease that is spread by mosquitoes. Two important
vectors are Aedes aegypti and Aedes albopictus, which also transmit dengue
virus. These species bite during daylight hours with peak activity in the early
morning and late afternoon. Both are found biting outdoors but Aedes aegypti
will also readily bite indoors. There is no direct person-to-person transmission.
Nature of the disease The name “chikungunya” derives from a Kimakonde word meaning “to
become contorted” and describes the stooped appearance of sufferers with
joint pain. Chikungunya is an acute febrile illness with sudden onset of fever
and joint pains, particularly affecting the hands, wrists, ankles and feet.
Most patients recover after a few days but in some cases the joint pains may
persist for weeks, months or even longer. Other common signs and symptoms
include muscle pain, headache, rash and leukopenia. Occasional cases of
gastrointestinal complaints, eye, neurological and heart complications have
been reported. Symptoms in infected individuals are often mild and the
infection may go unrecognized or be misdiagnosed in areas where dengue
occurs.
Geographical distribution Chikungunya occurs in sub-Saharan Africa, south-east Asia and tropical areas
of the Indian subcontinent, as well as islands in the south-western Indian
Ocean. (Map)
Risk for travellers In countries or areas at risk and in areas affected by ongoing epidemics.
Prophylaxis There are no specific antiviral drugs and no commercial vaccine. Treatment
is directed primarily at relieving the symptoms, particularly the joint pain.
Precautions Travellers should take precautions to avoid mosquito bites during both day
and night (Chapter 3).
COCCIDIOIDOMYCOSIS
Cause Coccidioides spp, a fungus
Transmission Coccidioidomycosis is transmitted by inhalation of fungal conidia from dust.
Nature of the disease The spectrum of coccidioidomycosis ranges from asymptomatic to influenza-
like illness to pulmonary disease or disseminated disease.
Geographical distribution Coccidioidomycosis occurs mainly in the Americas.
Risk for travellers The risk for travellers is generally low. Activities that increase the risk are those
that result in exposure to dust (construction, excavation, dirt biking, etc.).
