CHAPTER 7: OTHER
MEDICAL CONCERNS
7.1 This Chapter deals in
detail with each of the three other main medical concerns that
have arisen from our Inquiry, namely: the transmission of infection;
the effects of the cabin environment on vulnerable individuals;
and the handling of in-flight medical emergencies. The main non-medical
issues are then dealt with in Chapter 8.
Transmission
of infection
7.2 There is a widespread
general perception that the transmission of infection between
aircraft cabin occupants, both passengers and crew, is common,
and that this is facilitated by the nature of the cabin environment.
The general perception is reinforced by the personal anecdotes
we received in evidence (Appendix 4). As we note in paragraph
7.14, there are very few published reports of such cross-infection
in the scientific literature - although, of course, only serious
incident reports would achieve publication.
7.3 The clear view of all the health professionals
who submitted evidence to us is that, while cross-infection can
and does occur in the aircraft cabin, it does so because of the
crowding together of large heterogeneous groups of people. Although,
as pointed out by Professor Pavsol (p 264), there are good reasons
at first sight why the aircraft cabin environment should increase
the risk of cross-infection between its occupants, the reality
is that (apart from crowding) environmental factors in the aircraft
cabin appear to make little or no contribution to the transmission
of infectious agents. As noted in paragraph 7.16, most passengers
will mix with many more people - in crowded circumstances and
probably poorer environmental conditions - both before and after
their actual flights.
TYPES OF
INFECTION
7.4 There are three main
types of infection.
(a) VIRAL.
Viruses are sub-microscopic bodies which can multiply only
in living host cells. Common viral infections include: upper respiratory
tract infections (colds); influenza; measles; mumps; and chicken
pox. Viral infections are fought by the body's immune system,
antibiotics being of no use in dealing with viruses themselves.
Once the immune system has fought an infection for the first time,
it is usually able to deal more rapidly with any re-infection.
However, certain viruses, particularly those causing upper respiratory
tract infections and influenza, can mutate rapidly into strains
which the body does not recognise and thus has to fight again
as new infections.
(b) BACTERIAL.
Bacteria are larger than viruses but still microscopically small.
Unlike viruses, they can survive and multiply outside the body:
they are widespread throughout nature. Most bacteria are harmless,
and many are beneficial to humans: food digestion, for instance,
is very dependent on appropriate bacteria living in the bowel.
Harmful bacterial infections include: tuberculosis, pneumonia,
meningitis, and gastro-enteritis. The body defends itself against
bacteria and their toxic products by its immune and reparative
systems. Serious infections may be treated with antibiotics[92].
(c) PARASITIC.
Various parasites may use the human as a host, either permanently
or as part of their life-cycle, causing illness. Examples are
amoebic and other dysenteries; intestinal, other organ, and skin
worms; fungus infections of body and skin; malaria; and schistosomiasis.
7.5 Whether people exposed to infective material
then develop disease depends on various factors: the dose they
receive; whether they have any immunity; and their general state
of health. If the body's defences are weakened by infection or
disease, it is more susceptible to further infection. For example,
many of the complications of "colds" are due to secondary
bacterial infections of the affected membranes following their
viral infection.
7.6 Infections are spread through the air, by direct
or indirect contact (including through water, food and other ingested
material), and by the bites of insect "vectors". These
are considered in turn below.
AIRBORNE
TRANSMISSION
7.7 In airborne transmission,
the infective particles are discharged into the air in aerosols
produced by the sneezing, coughing and spluttering of those already
infected. The infections concerned are usually viral, although
bacterial diseases, notably tuberculosis, meningitis and pneumonia,
can also be spread in this way.
7.8 Human pathogenic viruses
generally remain infective for only a few minutes outside the
body; bacteria in suitable environments for up to a few days.
The duration of viability in both cases is dependent on the nature
and type of the organism, and on the physical conditions in the
environment into which it is released. Particularly relevant to
the aircraft cabin environment is that, as noted by Pall Aerospace,
dry air is thought to increase virus, and reduce bacterial, survival
times, but conditions in aircraft ventilation re-circulating systems
are generally not conducive to extended survival of micro-organisms
(pp 259). Whether people exposed to infective material actually
develop disease depends not only on the viability of the organism,
but also on the dose of the organism they receive. The latter
is related directly to the proximity of the source and, as Dr
Bagshaw of British Airways pointed out, the density of the cloud
of infective particles reduces rapidly with distance from the
source (Q 264).
CONTACT
TRANSMISSION
7.9 The primary means of
spreading viral, bacterial and some parasitic infections is by
contact. There are three main contact routes:
(a) skin to skin;
(b) accidental or purposeful exchange of body
fluids (blood, sexual fluids, saliva);
(c) absorption through points of entry to the
body, primarily mouth and nose, from direct contact with infectious
agents, or through intermediaries such as water and other beverages,
food, cutlery, sanitary and washing facilities, toilet articles,
clothing, bed-linen, and body wastes.
7.10 All of these are strongly
linked to personal and environmental hygiene. This gives rise
to concern because the aircraft cabin environment inevitably brings
into close physical contact peoples with different customs and
practices in relation to personal and general hygiene, together
with major constraints on sanitary, culinary, and waste disposal
facilities.
7.11 We received no evidence
or complaints about possible food-poisoning from in-flight catering.
Other than commending airlines and their agents for their high
standards of hygiene in relation to catering and encouraging their
maintenance, we make no further comment on the control and management
of food hygiene.
BITING
INSECTS
7.12 Some very serious infections
(such as malaria, yellow fever, dengue fevers and plague) are
spread by insect bites, including mosquitoes and fleas. There
have been reported cases of insect-spread disease near airports
in areas where the disease is not endemic[93]
where the assumption is that insects have been inadvertently transported
by aircraft. However, perhaps largely due to WHO's disinsection
procedures discussed in paragraph 4.24ff, transmission of infection
by insect bites has not been reported within the aircraft cabin
itself, and we consider this matter no further. Some fleas and
lice can be problematic as parasitic infestations in their own
right and, as noted briefly by Inflight Research Services (p 240)
there may be some cross-infestation in the cabin environment due
to proximity.
CROWDING
AND DISEASE TRANSMISSION IN AIRCRAFT
7.13 Bringing a mix of people
together in large numbers and in limited space would appear to
present ideal circumstances for spreading infections between them.
The more people present, the greater the risk that one or more
may be harbouring potentially infective organisms. Given the role
of proximity in airborne and contact transmission discussed above,
the more that people are crowded together, the greater the risk
of cross-infection. As we also note above, the higher the dose
of infectious organism to which people are exposed, the greater
the risk of contracting infection: flight sector length is thus
also important in defining the duration of exposure. A further
factor is that, with the continuing growth of air travel and a
wider range of national airlines on many routes, people from many
different countries are increasingly sharing flights and potentially
exposing themselves to new infectious agents against which they
have no immunity.
7.14 Against that background,
and bearing in mind that about 5 million passengers fly every
day, the number of reports of confirmed cases of on-board transmission
of infection between cabin occupants is amazingly small. In the
evidence we have received, the only widely-reported instances
from the professional literature appear to be two influenza outbreaks,
one of measles, three of tuberculosis (although WHO investigated
seven reported cases arising between 1989 and 1994) and a small
number of outbreaks of gastro-intestinal infections (pp 264 &
280). In addition, we received evidence from Anne Lewis (Appendix
4) about an outbreak of viral gastro-enteritis in an aircraft
setting, together with other personal reports about air-travel
related (mainly respiratory) infections. (Appendix 4).
7.15 There is also some serious
misreporting. For example, our attention was drawn to a newspaper
article[94]
reporting a case of two people infected with TB during a flight.
In fact, testing carried out by Dr Perry had shown that they were
not so infected (p 267).
7.16 The incidence of infectious
illness among those millions of passengers is, of course, bound
to be much higher than indicated by the above figures, but it
is obviously wrong to attribute all air travel-related illnesses
to cross-infection in the aircraft cabin. Many of the cross-infection
risks in the cabin during flight are not unique to that environment.
Similar close-contact situations arise elsewhere, not least at
the margins of air travel such as airport lounges and buses, in
other forms of mass transport, and in restaurants, bars and places
of public entertainment.
7.17 On the evidence we have
been given, it seems to us that the risk of transmission of infection
due specifically to being in the aircraft cabin environment is
no greater than elsewhere, at least in relation to major illnesses,
provided circulation and filtration systems are working properly.
For lower level illnesses such as coughs and colds, it seems very
unlikely that conclusive evidence could be obtained to point one
way or the other. Given the evident success in avoiding transmission
of major infections, we do not agree with those who seem keen
to attribute any travel-related infectious ailment to augmented
transmission within the aircraft cabin environment.
7.18 The small number of confirmed cases of flight-related
cross-infection is a call for continued vigilance rather than
an excuse for complacency. As discussed in the immediately following
section, aircraft manufacturers and operators go to very great
lengths to reduce the chances of cross-infection between cabin
occupants to as low a level as practicable with current technology.
We also consider in paragraphs 7.34ff the control of intending
passengers infected with transmissible conditions, and of post-flight
monitoring, with the aim of understanding better, and thus reducing
further, the possible risk of cross-infection in the aircraft
cabin.
CABIN VENTILATION
AND FILTRATION
7.19 A common allegation
among those summarised in Appendix 4, and echoed in other evidence
and the media, is that modern cabin ventilation systems appear
to facilitate - indeed encourage - cross-infection. As discussed
above, this is not supported by the facts. Features which could
promote cross-infection are longitudinal flows of air within the
cabin and ineffective filtration of the re-circulated air.
7.20 In older aircraft, the general flow of ventilating
air was from the front to the back of the cabin. Both Airbus Industrie
and Boeing stated unequivocally that, in modern aircraft, the
airflow is from the top of the cabin downwards to the floor (Q
428, p 204). Airbus told us that they use the latest mathematical
modelling design techniques to ensure this, and that they test
within their aircraft that the design flows are achieved and that
"dead zones" are avoided. They also said that this would
be unaffected by seating configurations (QQ 428 & 429). Any
transmission of an infectious agent from an affected passenger
would therefore seem to be physically limited to those passengers
within the immediate vicinity. This is at least similar to - and
probably better than - conditions in any ground environment where
numbers of people are gathered closely together.
7.21 As discussed in Chapter 5, half the cabin air
is re-circulated through filters, and then mixed with an equal
volume of fresh air (which, as noted in paragraph 5.6, is bacteriologically
sterile - again better that most ground level "fresh"
air) before the next pass. If there were no filtration, infectious
organisms given off continuously by a cabin occupant would be
dispersed throughout the cabin atmosphere, on the face of it presenting
a significant risk of infection to all cabin occupants. However,
progressive dilution with fresh and re-circulated air and removal
by air extraction overboard would lead to a general cabin level
of infectious organism greatly lower than that in the immediate
vicinity of the infected person. Thus, even in the absence of
filtration, the level of infectious agent to which most cabin
occupants would be exposed is very small though they would be
so exposed for the duration of the flight.
7.22 The Air Transport Users Council (AUC) expressed
concern about cabin conditions on the ground when the aircraft
ventilation system was not operating. They would like to see enacted
a US National Academy of Science recommendation that full auxiliary
ventilation should be used, or passengers removed after 30 minutes
without it (QQ 155 & 161). Dr Dawood was of a similar view
(p 220). The AUCs' concern was associated with the risk of cross-infection
between cabin occupants as occurred with influenza in the Alaska
Airlines incident in 1977 (Q 162). ATA also considered hold-ups
on the ground with no aircraft ventilation to be a risk factor
for transmission of communicable diseases (p 110). To
reduce cross-infection risks (as well as for general comfort),
we recommend airlines to ensure that they have suitable policies
for occasions when aircraft with passengers on board have to be
held on the ground for extended periods without full ventilation.
Such events are rare, so it is all the more important to have
in place clear guidelines for action.
7.23 Efficient filtration
(a topic introduced in paragraphs 5.18ff) is essential to minimise
the potential for cross-infection in aircraft using re-circulatory
ventilation. Evidence from airlines was that the HEPA filters
they used remove bacteria and virus particles with an efficiency
of over 99% (pp 99, 107 & 104) although they appeared only
to be quoting filter manufacturers' claims. Airbus Industrie and
Boeing reported only the filter specifications (pp 165 & 204).
Because the standard particle size tests noted in paragraph 5.21
may not accurately reflect microbiological effectiveness, Pall
Aerospace tests its own HEPA filters with bacteria and viruses.
These have been found to remove microbiological organisms with
an efficiency greater than 99.999%, which Pall have stated is
the "microbial equivalent of a 100% outside air single-pass
system" (p 259). Furthermore, Pall calculates that, even
with a significant rupture (of 10mm by 1mm), such a filter would
still provide for 99.9% efficiency (p 259).
7.24 Although we do not
dispute the design claims for HEPA filters, we fail to see how
the industry can effectively rebut charges that such filters do
not perform as designed when so little attention is given to their
performance. For example:
- they are replaced "on time" rather
than "on condition"[95];
- they are not subject to regular between-replacement
or post-replacement inspections;
- they have been shown to remove viruses only in
laboratory tests; and
- no routine monitoring of air contamination by
sampling is carried out.
We note the point made by Airbus Industrie and Pall
Aerospace that newer systems are fitted with differential pressure
gauges which indicate damaged or blocked filters (pp 165 &
259), but this may not be enough and we recommend the industry
as a whole to review and substantially improve overall in-service
performance monitoring of filters.
7.25 The theory, the facts
and the vast majority of our specialist witnesses all support
the conclusion that HEPA filtration, if properly installed and
maintained, should remove the possibility of cross-infection that
would otherwise exist in re-circulatory cabin air systems. We
agree that, on the evidence presented to us, the modern aircraft
cabin environment generally poses no greater risk of transmission
of infection between its occupants than crowded situations elsewhere
- and may, indeed, be safer than most of them.
7.26 As noted in paragraph
5.22, however, HEPA filtration is not yet standard. To minimise
the risk of cross-infection, we are clear that it should be, and
we recommend the Government and regulators to make filtration
to best HEPA standards mandatory in re-circulatory systems.
In the meantime, we recommend airlines to upgrade all filtration
to the best HEPA standards.
7.27 We noted[96]
that, feeding on fears about poor cabin air quality, Mr Kahn's
Aviation Health Institute was selling face-masks which were stated
to "screen out 98% of bugs including TB". We cannot
see how these would be of any practical use unless the wearer
happened to be sitting directly next to someone with an active
bacteriological infection (and there was also a good fit of the
mask to face). Additionally, Professor Denison warned of the dangers
to certain vulnerable passengers of the wearing of face masks
(Q 215).
7.28 It came to our notice that there were other
technologies under development that might supplement or replace
HEPA filtration for aircraft cabin ventilation. AEA Technology
provided us with an outline of their work on plasma (ultra-violet,
electron, and free-radical bombardment) techniques for air sterilisation
(p 197). The technology is interesting and, when more fully developed,
may be found to have advantages over present systems of filtration.
POTENTIALLY
INFECTIVE PASSENGERS
7.29 The only way of eliminating
any risk of cross-infection in the aircraft cabin would be to
prevent intending passengers carrying transmissible infections
from flying. This is simply not achievable. The incubation period
(the time between initial infection and the appearance of symptoms)
for most viral and bacterial infectious diseases is typically
several days or even weeks. A person may be highly infectious
during this period, and remain infectious even when the disease
is obviously present. Moreover, those who have been in contact
with infectious diseases against which they have immunity may
nevertheless be capable of infecting others.
7.30 It would clearly benefit fellow passengers if
people did not fly in such circumstances. Ideally, individuals
who thought that they might be infectious would either identify
themselves and postpone their flight or request advice from their
medical advisers or the airline about their fitness to fly. Such
actions place great demands on individuals' honesty.
7.31 Flying for either business or pleasure tends
to be part of significant journeys or events which may be difficult
to disrupt. In addition, many people will have non-refundable
tickets, leaving costs to be reclaimed through any insurance arrangements.
There must be an understandable tendency for intending passengers
to "feel well enough to fly", and not to consider any
potential hazard to others. It would be a counsel of perfection
to expect passengers with minor coughs and colds to defer their
flights. The test for individuals must be whether, if they themselves
were well, they would be happy to sit next to someone in their
own present state of ill health.
7.32 Airlines can, of course, refuse to fly passengers
they consider may be a risk to others. As Delta Air Lines pointed
out, pre-boarding ground staff or cabin crew are likely to be
alert to this, and will refuse to board a passenger who may obviously
be a risk to others boarding the flight concerned (p 224). At
most major airports, pre-boarding staff are able to refer to airline
or airport health professionals for advice. As in all cases where
an intending passenger may present risks to the safety of the
aircraft, its crew, or its passengers, the final decision whether
to carry the person rests with the aircraft captain.
7.33 As part of improved
health information for intending passengers discussed in Chapters
8 and 9, we recommend the Government and airlines to do more to
dissuade intending passengers from flying while they are likely
to infect others. This could be further reinforced by a reminder
that boarding may be denied to those who are obviously infectious.
POST-FLIGHT
CONTACT TRACING
7.34 WHO's International
Health Regulations (1969 with subsequent updates)[97]
are incorporated into the national public health regulations of
individual countries. The Regulations seek to minimise the international
spread of disease, and set out various requirements for handling
outbreaks of specific infectious disease, currently plague, cholera,
and yellow fever, cases of which have to be notified to international
and local public health authorities when discovered. Those pertaining
to aircraft are incorporated into national civil airline regulations.
(From time to time, WHO also issues non-mandatory recommendations
concerning other transmissible diseases, those currently in force
being concerned with TB, malaria and AIDS/HIV.)
7.35 The Regulations and recommendations detail preventive
and hygiene control measures to be taken by national health administrations,
and they can impact directly on airline passengers; for example,
if a specified infectious disease is notified on or before the
landing of a flight, the aircraft may be impounded so that passengers
can be medically inspected and contact details taken. National
authorities may also apply the regulatory measures locally for
other infectious diseases if they are concerned about incoming
or outgoing spread of potentially epidemic diseases.
7.36 One of the main purposes of notification is
to enable local authorities to trace contacts of the infected
case. Given that incubation periods are frequently several days
or even weeks, the initial notification is usually made by a health
professional some time after the flight concerned. The airline
or its agents may already have disposed of any useful information
about individual passengers by then. Such late notification may
still lead to the initiation of contact tracing by the local authorities,
but airlines have no direct responsibilities in this regard. They
may, however, be able to assist the authorities by providing tracing
information that they may hold on crew and passengers.
7.37 In their recent investigations into TB cross-infection
in aircraft, WHO found that the only information generally available
from airlines seemed to be passengers' names, usually contact
telephone numbers (through ticket sellers), and allocated (although
not necessarily occupied) seats. Ticket agents may have better
contact details, but this information may remain available for
only a short time after a flight. Some information may also be
available from immigration and customs declaration landing cards
in the case of some passengers on incoming international flights,
but this has not been a useful source for follow-up purposes.
7.38 Given those difficulties, it is unsurprising
that WHO finds that the financial and labour costs of contact
tracing for epidemiological purposes are out of all proportion
to the value of the results achieved. The primary purpose of the
notification and tracing arrangements remains simply to enable
health authorities to inform people that they may have been exposed
to an infected person during the flight and to advise them that
they should seek medical advice.
7.39 Despite this rather pessimistic view of the
value of seeking to trace contacts after passengers have dispersed
post-flight, we are of the view that such procedures should not
be dismissed out of hand. Although the need for contact tracing
might be infrequent, there seems little necessity (given modern
data-storage systems) for airlines and their agents to dispose
quickly of potentially important passenger details. We
were pleased to note the comment from Mr Nafzger of DETR (Q 34)
that there probably should be some sort of recall system, and
that his Department was discussing this with DoH and the airline
industry.
7.40 To help with post-flight
contact tracing when exposure to serious infections may have occurred,
we recommend the Government to consider requiring UK airlines
and their agents to retain all aircraft passenger information
which could be useful in tracing contacts for a minimum of three
months after all flights, and that the Government should seek
to extend this requirement internationally[98].
We also recommend airlines and their agents to move towards this
immediately.
7.41 From time to time,
airlines and their representative bodies review the passenger
data collected for marketing and other analytical purposes. In
doing so, we recommend they also consider improving such data
(or at least ensuring greater standardisation) to help meet the
potential needs of post-flight contact tracing.
92 As discussed in our Report Resistance to Antibiotics
and Other Antimicrobial Agents (7th Report Session 1997-98,
HL Paper 81-I), care must be taken in the use of antibiotics to
reduce the pressure on bacteria to mutate into resistant forms. Back
93
Such as airport malaria as reported in the August 2000 issue of
the Bulletin of the World Health Organisation. Back
94
It's high-flyers who may be laid low, Daily Telegraph,
22 June 2000. Back
95
That is, by reference to some pre-set period rather than when
a specified condition is reached. Back
96
From the article Breathe Easy, Style magazine, Sunday
Times, 25 June 2000 - which repeated the serious misreporting
already noted in paragraph 7.15. Back
97
Throughout this section, we have drawn on the provisions of these
Regulations and on WHO's Tuberculosis and Air Travel: guidelines
for prevention and control, WHO/TB/98.256. Back
98
Although the risk of infection generally increases with the duration
of the flight, the evidence shows that virus infections have been
transmitted while an aircraft is on the ground before a relatively
short flight. Passenger data therefore need to be kept for all
flights. Back
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