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Probable measles transmission during transatlantic travel
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Editorial Board
Dr D O'Flanagan, HPSC
(Managing editor)
Dr L Kyne, RCPI (Paed)
Prof C Bradley, ICGP
Dr N O'Sullivan, ISCM
Mr E O'Kelly, NVRL
Dr P McKeown, HPSC
Dr L Thornton, FPHMI
Dr C Bergin, IDSI
M Kelly, HPSC
(Editor)

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Probable measles transmission during transatlantic travel

Summary

In January 2010, during a period of high measles activity in Ireland, three Irish children travelled to, and returned from, the USA while infectious with measles.  A total of 321 passengers were potentially exposed during both flights. Public health notification of this event triggered a contact tracing exercise to identify at risk individuals and provide advice and prophylaxis if needed. Two months later a follow up of passengers was undertaken by HPSC to identify if any secondary cases among passengers had occurred as a result of exposure on the plane or in transit. Contact tracing of Irish passengers did not identify any secondary measles cases among Irish residents but contact tracing undertaken by United States (US) authorities identified two cases in US residents.

Background

On January 14th 2010 HPSC was informed by a regional Department of Public Health that three siblings with probable measles had travelled to, and from, the United States during the previous six days. The children, all of whom were unvaccinated with MMR, were symptomatic with cough and sniffles (attributed to a ‘cold’) on the flight from Ireland  to the USA. The following day they developed a rash. They were not seen by a doctor while in the United States. They travelled back to Ireland on the fourth day after rash onset.  Of relevance, an unvaccinated sibling of these children had been diagnosed with measles by a GP eight days prior to this event (‘index case’). The index case in turn was known to attend a school at which a measles case had already been notified a number of weeks before. HPSC considered this incident a significant public health threat to non-immune fellow passengers on both flights.

On January 15th the flight details were provided to the HPSC and these were forwarded to the airline in order to obtain passenger information (passenger numbers, and contact details). HPSC forwarded flight information to U.S. Centers for Disease Control and Prevention (CDC) on January 15th. CDC promptly initiated contact investigations for both flights according to their national protocol (contacts identified as passengers seated in the same row as, the two rows in front of, and the two rows behind the index cases, plus any babes in arms of adults seated anywhere on the plane, and crew members serving passengers in the same cabin as the index cases).  CDC provided names and contact information of Irish citizens or residents identified as contacts to HPSC for contact tracing. Irish passengers were initially contacted by the airline and subsequently by Departments of Public Health and later by the HPSC.  

Methods

Contact tracing of passengers on the same flights as the cases was undertaken in collaboration with the airline on which the cases travelled. The airline obtained the contact details for passengers from their passenger booking information system on the 15th of January. The list was reviewed by HPSC and passengers were characterised by country of residence based on booking information provided; residents of Ireland (Irish passengers), or other countries (non-Irish passengers).

Between January 15th and 17th the airline tried to telephone contact all those Irish passengers who had provided telephone contact details at the time of booking, regardless of where they may have been on the plane (passenger seating information was not available at this time). Airline staff used a standard message that had been developed by HPSC. Contacted passengers were informed that they may have been exposed to measles on the flight and that they, or those they travelled with, if not already immune to measles, may be at risk of developing the disease. If they became unwell they were advised to contact their GP or the HSE. Passengers considered to be at particular risk (infants aged 5-12 months, non- immune individuals or pregnant women), for whom immunoglobulin might be required were advised to contact the HSE and provided with a contact telephone number of a senior HSE staff member. The airline also informed the flight crew of their possible exposure. In the following days, HSE Departments of Public Health attempted to contact those Irish passengers whom the airline had been unable to contact. This was done using telephone, email or postal address (if provided).

CDC contacted those passengers that were US citizens or residents and were identified as being contacts according to US protocol (outlined in the background section of this report).

HPSC informed the national health authorities of non-Irish passengers from Spain and the U.K. so that contact tracing of those passengers could be done according to their national protocols. Spain contact traced the two passengers in their jurisdiction and the UK, following their own risk assessment, did not undertake contact tracing of the passenger in their jurisdiction.  

In addition to the above contact tracing immediately after the event, in April 2010 HPSC sent a standard email to those 130 Irish passengers with email addresses and sought information on rash fever illness among the passengers in the 21 days after travel. The airline was also asked about measles illness among crew for the same time period. Contact was again made with the public health authorities of Spain, the UK and the US to ascertain if they were aware of, or could determine, if any cases had occurred following this exposure.  

Results

Three hundred and twenty one passengers were identified on the passenger booking information lists for the two flights; of whom 159 were identified as being resident in Ireland (based on address or telephone number information). A total of 142 Irish passengers booked on line and 27 booked with travel agents.  

Between January 15th and 17th the airline successfully contacted by telephone 91 (57%) of all the Irish passenger bookings; 68 Irish passengers could not be contacted by telephone (no answer or incorrect telephone number). The airline had contact email addresses for 48 of the 68 Irish passengers who were not contacted by telephone. Departments of Public Health attempted to contact these passengers using either email (n=22), trying phone (again) (n=4) or letter for some (n=5). It was not possible to contact 20 passengers using this method. Although travel agents were informed, it is unclear if they were able to contact their clients as most travel agents do not keep client contact details after the flight has occurred.

For the follow-up in April, 130 Irish passengers with email addresses were identified from the lists provided by the airline. 62 responded (response rate 45%), none of whom reported rash fever illness.

The United States reported that measles was diagnosed in two young, unvaccinated children (babes in arms), aged 12 and 24 months, who were seated 9 and 11 rows from the index cases on the flight from Ireland to the U.S. Rash onset was 15 days after the flight, which was within the incubation period (7-21 days after exposure).

No measles cases were reported for the three passengers from European countries. Spanish authorities had followed up on the two passengers (both adults) in their jurisdiction and reported that neither had developed rash illness (one reported vaccination as a child and another stated that they had measles as a child). The UK did not follow up on the passenger from their country (following UK protocols) but were able to confirm that this individual had not been reported to public health with measles at any time since the flight.

The airline reported that no measles cases were reported among crew staff.

Discussion

Two United States based children developed measles 15 days after return from Ireland. Although neither child was seated in close proximity to the cases the possibility that flight or in-transit exposure occurred cannot be out-ruled and is considered the most likely source for their infection. Exposure to measles virus prior to travel, although possible, is considered less likely, as parents of these children were not aware of direct contact with measles cases while in Ireland.

Although close direct contact between the US cases and the Irish cases was not demonstrated (seating distance was 9 and 11 rows) it is possible that the Irish cases and the US children may have been in close proximity at some point during transit or while on the plane. However, even without closer proximity, measles transmission via aerosolisation has been previously reported, with acquisition reported among cases who attended the same GP surgery within a couple of hours after an index case has left a room but was not in direct contact with the secondary cases.1

The contact tracing effort undertaken in Ireland required close collaboration with the airline. The purpose of the contact tracing was to identify those passengers who might benefit from prophylaxis (immunoglobulin). As more than 72 hours had elapsed since exposure vaccination for non immune individuals was not advised as the vaccine needs to be given within 72 hours of exposure to prevent disease The contact information provided at the time of booking was the only source of information for the contact tracing undertaken in here and was found to be inaccurate for many passengers..The booking information did not provide sufficient information to identify babes in arms (only one infant was identified on the booking list). This young group includes those most likely to be non-immune and who are at particularly high risk of measles infection and complications. Consideration should be given to ensuring that passengers are aware of the need to provide accurate contact information when booking, and also the purposes for which this information may be used. The importance of identifying babes in arms has been highlighted in this event. Dialogue between airlines and public health is needed to determine how such information can be obtained using current information systems.

In contrast to the time and effort used by the airline, HPSC and HSE Departments of Public Health to contact passengers, the United States authorities appear to have been able to obtain and contact the passengers (n=39) in their jurisdiction more quickly. Agreements, regulations, protocols and information systems are well established in the United States and work is currently ongoing in Ireland to increase the capacity to respond more quickly to similar events.

The decision to contact trace fellow passengers after identification of individuals with infectious disease on public transport is based on risk assessment, and the available evidence. The benefits to the individual and public health (preventing disease and onward spread) versus the cost of such an undertaking and the use of valuable resources need to be considered. Identifying those most likely to be at risk is more efficient. In relation to the event described in this report, we highlight two different approaches undertaken. The US approach focused on those passengers in closest proximity to the cases and babies held in arms anywhere in the plane. As the risk for these passengers is most likely to be highest this approach is justified. The Irish approach was to try to contact all Irish passengers and was, in part, based on the recent experience of a national measles outbreak, involving both children, and adults, and an awareness that among the Irish population there are pockets of non-immune individuals in all most age groups. This approach, in the end, was particularly resource intensive and failed to identify any Irish cases. Whether a more targeted approach would have been better should now be considered but would also require more timely and complete information for maximum success. Although the specific cost incurred to the airline and public health has not been defined we estimate that they were considerable, in terms of the time that staff spent on this activity.

The value of having pre-agreed processes in place, such as in the United States between public health authorities, airlines and other agencies would appear to facilitate a more rapid response to contact tracing, and an ability to focus on those considered most at risk (either because of seating proximity or because of age < 2 years). Similar agreements and processes, if pre-agreed in Ireland (prior to such events occurring), could improve the access to this type of information in a timely manner so that future contact tracing activities could be done quickly and efficiently. Although age of passengers is not routinely collected methods of identifying babes in arms more accurately should be explored. 

The fact that these children travelled while infectious could have been avoided if the index case had been notified to public health by the diagnosing GP. As a result of this omission, opportunities to provide MMR to the children, and to provide advice to the parents on the need to be alert to disease and to avoid exposing others to the disease could not be made. It was particularly unfortunate that the parents of these children were not informed of the risk that they posed to other non-immune individuals. These children, none of whom were vaccinated or had a previous history of measles, were at high risk of measles following exposure to the index case and were likely to transmit it to non-immune individuals. Air travel in this instance would not have been advised in these circumstances as transmission has previously been reported (but risk may depend on background immunity of fellow passengers).2-5

 Measles is one of the most infectious diseases known to man. Prior to the widespread availability of a measles vaccine infection was nearly universal during childhood and more than 90% of persons were immune by age 15 years. Measles is still common and often fatal in developing countries. This report highlights the infectiousness of measles and the importance of vaccination in preventing disease. Parents should be informed and made aware of the implications to their children, and to other children and older individuals, when they do not vaccinate their children with MMR. The risk posed to other susceptible children, many of whom may be too young for vaccination is well recognised.

Our experience from this outbreak will inform future contact tracing activities with regard to measles. Additionally, continued efforts are being made to ensure that all children are age appropriately vaccinated with MMR.

Suzanne Cotter, Darina O’Flanagan, Fionnuala Cooney, Lelia Thornton, Paul McKeown, HPSC

Acknowledgements

HPSC wishes to thank the collaboration and support of HSE Departments of Public Health, and Public Health Colleagues from Spain (Spanish EWRS team), the UK (HPA) and the USA (CDC).

References

1. Bloch AB, Orenstein WA, Ewing WM, Spain WH, Mallison GF, Herrmann KL, Hinman AR. Measles outbreak in a pediatric practice: airborne transmission in an office setting. Pediatrics. 1985 Apr;75 (4):676-83.

2. Amornkul PN, Takahashi H, Bogard AK, Nakata M, Harpaz R, Effler PV.Low Risk of Measles Transmission after Exposure on an International Airline Flight. J Infect Dis. 2004 May 1;189 Suppl 1:S81-5.

3. Coleman KP et al. Measles transmission in immunized and partially immunized air travellers. Epidemiology and Infection 2010; 138:1012-1015

4. Dayan GH, et al. The cost of containing one case of measles: the economic impact on the public health infrastructure – Iowa, 2004. Pediatrics 2005; 116: e1–4.

5. de Barros F, et al. Measles transmission during commercial air travel in Brazil. Journal of Clinical Virology 2006; 36: 235–236.

 

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