Revised guidelines for the follow-up of communicable diseases reported among travellers on aeroplanes
In June 2004, the Communicable Diseases Network Australia issued a statement on the Follow-up of communicable diseases reported among travellers on aeroplanes. These guidelines have now been revised, in November 2006, and include advice on measles.
In June 2004, the Communicable Diseases Network Australia issued a statement on the Follow-up of communicable diseases reported among travellers on aeroplanes [see: ]. In November 2006, CDNA revised these recommendations and included advice on measles.
From time to time health departments will be notified of patients who have been diagnosed with a communicable disease and have travelled in an aeroplane while infectious. A risk-based approach is taken when considering the need for public health intervention.
What influences the risk of infection?Aeroplane travellers could carry a variety of infections. Some of these may be spread through the air (such as tuberculosis and measles), by direct droplets (such as influenza and pertussis) or by hands and fomites (such as norovirus infections).
The risk of transmission to travellers will vary according to the disease, the infectiousness of the case, the mode of transmission, the ventilation in the aeroplane, the dose of the exposure (which depends on duration and proximity), and their susceptibility to that infection. For some infections, the risk may extend beyond travellers and crew on the aeroplane, and include people exposed en route to and from the airport, and workers and other travellers at the airport.
The air-handling systems of large aeroplanes are generally designed so that recycled air passes through HEPA filters and then travels transversely across the aeroplane (i.e., along rows of seats) rather than up and down the body of the aeroplane. This pattern tends to limit most of the risk of any airborne transmission to people in the same or adjacent rows of seats to the infectious passenger, and the filtering further reduces the chance that the air will contain infectious agents. 
Public health aims of follow up of aeroplane travellersPriorities must be set in balancing the resources required to prevent potential disease against the burden that disease is likely to have on the community. The data available to guide when passengers should be contacted are patchy, however. In determining whether the contacts of an infectious aeroplane traveller should be contacted about their possible exposures, the following parameters should be considered:
- the risk of transmission
- severity of the disease
- the prevalence in the general community (i,e., the relative likelihood that passengers will be exposed to the infection elsewhere, and the need to keep certain diseases – eg, quarantinable disease and measles – out of the country)
- existing recommendations for prevention
- whether an effective intervention can be delivered before the onset of disease.
The overall risk to exposed passengers from infectious disease in general is low.  Contact-tracing of passengers who share flights with infectious cases can be expensive and incomplete  because of the lack of reliable contact details provided by passengers on the landing cards or airline bookings. However, some infections that have a low prevalence in the Australian community -- such as tuberculosis, meningococcal disease, measles and novel new strains influenza -- require special consideration.
TuberculosisThere is some evidence that tuberculosis may be transmitted on long flights,  and the World Health Organization recommends that where a person with infectious tuberculosis has travelled on a commercial flight of more than 8 hours duration in the previous three months, the airline company should inform others who were seated in the two rows in front and the 2 rows behind the infectious case, of the risk.
Meningococcal diseaseTransmission of meningococcal infections between passengers is very rare. In 2001 the US Centers for Disease Control and Prevention found no reports of secondary transmission of meningococcal disease among airline contacts  but nonetheless recommended that for flights of more than 8 hours, chemoprophylaxis be given to passengers in the seats directly beside a case. The only reported incidence of possible transmission of meningococcal disease on an aeroplane was identified in 2003, between two passengers who travelled in different sections of the same aeroplane from Los Angeles to Sydney. 
MeaslesRecent US studies found that transmission on aeroplanes is very rare, occurred (where known) to passengers sitting adjacent to infectious cases,  and that the public health value in following up fellow aeroplane passengers was questionable.  In Australia over the last decade there has been no report of measles transmission on an aeroplane to people considered susceptible (i.e., born after 1965). (Although a possible transmissions was reported in an older person travelling in Australia and another travelling overseas who would not be considered eligible for intervention). The lack of transmission is likely due to the high rate of immunity in the travelling Australian population, and possibly the air handling mechanisms on board flights.
Other notable infectious diseasesThe risk of non-immune aeroplane travellers contracting seasonal influenza, chickenpox and pertussis and other common respiratory infections on long flights is not well documented  but given what is known about their transmission, is probably moderate. These infections are relatively common in the general community and the Australian Immunisation Handbook  has preventive advice for those wishing to avoid them. Therefore tracing fellow passengers exposed to these conditions would be unlikely to have much impact on the overall incidence of these conditions in the community.
Most enteric infections are spread though contaminated food or water and with the exception of norovirus infection, the risk of spread from one aeroplane traveller to another is generally low. Norovirus is thought to be transmitted via aerosol or direct person-to-person contact, especially in confined spaces. However this infection is very common in the general community, the incubation period is short, victims completely recover after a brief -- albeit unpleasant – illness, and there is no post-exposure intervention. While outbreaks of cholera have been reported among aeroplane passengers, these have been associated with eating contaminated food rather than person-to-person spread. 
For quarantinable disease (including avian influenza, SARS, smallpox, plague, yellow fever, rabies and viral haemorrhagic fevers) the risk is variable and fellow travellers would need to be managed on a case-by-case basis.
Before departureTo prevent infections among travellers on aeroplanes from occurring in the first place. Potential travellers should:
- seek medical advice well before international travel to ensure any pre-existing and travel specific health issues are managed, including administration of vaccinations, antimalarial drugs, and advice about reducing the risks of food, water, mosquito born and other diseases.
- be immune to measles, mumps and rubella, regardless of destination
- check that they are protected from chickenpox, influenza and pertussis if they wish to avoid these infections (see the current edition of the Australian Immunisation Handbook for recommendations, available from );
- if unwell immediately before travel, seek medical advice about whether travel should be delayed (for their sake and the sake of fellow travellers). In generally, anyone with fever, vomiting, diarrhoea or the infections listed in the table should delay travel
- follow simple hygiene measures to minimise the spread of infections: covering coughs and sneezes with a disposable tissue, and wash hands with running water and soap regularly, especially after blowing the nose or using the toilet. Airlines may provide passengers who are coughing with a mask.
Follow up of travellers exposed to an infectious passengerThe table provides an arbitrary summary of these parameters for selected diseases. For serious infections spread through the air, follow-up is only useful for those aeroplane passengers who were seated in same or adjacent rows (two rows forward and back) as an infectious passenger (if more than 8 hours for tuberculosis, or for any flight for measles). For meningococcal disease, follow up is only worthwhile for passengers who were seated immediately next to an infectious passenger for more than 8 hours; where the infectious person was seated at an aisle, follow up would not routinely be required for the person on the other side of the aisle. The value of following up contacts of other cases seems limited, except in the rare case of a serious exotic diseases such as pneumonic plague, viral haemorrhagic fevers or SARS, or avian or pandemic influenza. These need to be dealt with on a case-by-case basis.
- Eberhart-Phillips J, Besser RE, Tormey MP, et al. An outbreak of cholera from food served on an international aircraft. Epidemiol Infect 1996;116:9-13.
Other Quarantinable diseases
Risk of transmission
|Moderate||Low because of high rates of immunity||Moderate if smear positive case exposed >8 hours||Low among most adult travellers because of childhood infections||Very low||Unclear: probably moderate if >8 hours flight||Low. Moderate for norovirus||Variable|
Prevalence in community
Existing general recommendations for prevention
|Immunise||Immunise||No||Immunise||Early detection of symptoms, immunise||Immunise||Hand-washing||Variable|
|Antiviral drugs||Immunisation <72 hours, Immuno-globulin <7 days||Screening, preventive therapy||Immunisation or varicella-zoster immuno-globulin||Clearance antibiotics||Preventive antibiotics||No||Variable|
|No||Seats in same row, 2 rows forward and 2 rows behind||Seats in same row, 2 rows forward and 2 rows behind, if flight >8 hours||No||Seat beside if >8 hours||No||No||Consider for viral haemorrhagic fevers, plague, avian influenza|