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Volume 29-12
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ASSESSMENT OF IN-FLIGHT TRANSMISSION OF SARS - RESULTS OF CONTACT TRACING, CANADASevere acute respiratory syndrome (SARS) has been described in Asia, North America, and Europe. SARS is characterized by fever, malaise, cough, dyspnea, and infiltrates on chest radiograph, which may progress to severe atypical pneumonia or acute respiratory distress syndrome (ARDS) in severe cases. Current evidence suggests that a novel coronavirus is associated with the disease. SARS was first identified in Canada on 13 March, 2003. As of 7 May, 2003, there have been 146 probable cases, 183 suspect cases and 23 deaths attributed to SARS in Canada(1). At present, epidemiologic evidence indicates that SARS is transmitted during close contact with an infected person through respiratory secretions, although other routes of transmission are being considered. Given this mode of transmission, there is concern that SARS may be transmitted during air travel. This report provides an overview of the surveillance and policy measures that Health Canada has implemented to address this concern as well as the initial results of passenger contact tracing. Surveillance and Contact Tracing Health Canada's Centre for Infectious Disease Prevention and Control SARS response team, in collaboration with the Centre for Emergency Preparedness and Response (CEPR) and provincial and territorial ministries of health, has been conducting passenger contact tracing to identify any secondary transmission associated with air travel. The relevant provincial or territorial ministry of health initiates the investigation by notifying CEPR of a case who was symptomatic while travelling by air. CEPR requests the flight manifest (including passenger name and seat location) and the passenger contact list from the appropriate airline, then compiles these lists for each jurisdiction, and forwards them to the appropriate provinces and territories. The passenger contact list can be problematic, as it does not always include the passenger's contact information. In some cases, only a booking agency contact (e.g. travel agent) will be provided. Because of the resultant delays, CEPR has recently implemented the collection of passenger contact information on selected flights from Asia (Viet Nam, Singapore and the People's Republic of China, including Hong Kong Special Administrative Region and Taiwan) using a Traveller Contact Information Form (TCIF). This new system was developed in an effort to make contact information more quickly available, so that passenger follow-up could be initiated in a more expedient manner. Once contact information has been received, local health authorities contact appropriate passengers to determine their health status in the 10-day interval (one full incubation period) after potential exposure to a SARS patient on the flight. The results of contact tracing are collated by Health Canada, and summary information is reported back to the provinces and territories. Public Health Measures and Infection Control SARS and Air Travel Guidelines have been developed by the National SARS Public Health Measures Working Group in response to a need for recommendations regarding the follow-up of passengers when a person identified with SARS has travelled by plane. These guidelines were developed on the basis of current knowledge and have undergone revisions as additional information has become available. From 13 to 21 March, 2003, contact tracing of passengers included follow-up of passengers seated close to the probable case (i.e. people seated in the same row as the case, two rows ahead and two rows behind the case). Contact tracing was initiated only if the probable case was symptomatic during travel. Beginning 22 March, contact tracing was expanded to include passenger follow-up when a suspect case of SARS was identified and was known to have been symptomatic during air travel. Beginning 31 March, all passengers were followed up whenever a suspect or probable case of SARS was reported and was known to have been symptomatic during the flight. However, the type of follow-up and the recommendations vary by the status of the case (suspect or probable) and the proximity of seating in relation to the case (Table 1). In addition to the SARS and Air Travel Guidelines, the following infection control policies related to air travel have been developed:
These infection control guidelines and the SARS and Air Travel Guidelines are available on Health Canada's Website (http://www.sars.gc.ca). Results In Canada, there have been a total of five probable cases (5/146 or 3.4%) reported with a travel-related exposure to a SARS-affected area in Asia. Of these, only three were symptomatic during flight and required passenger follow-up. One additional probable case, exposed through household contact, was symptomatic on a flight between Canada and the United States. As of 8 May, 2003, there were 14 suspect cases who were symptomatic during their flight, for a total of 18 cases known to be symptomatic during air travel. Ten (56%) of them travelled on two or more flights, for a total of 29 implicated flights requiring follow-up. |
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Passenger contact information has been obtained and processed for 17 of the 29 flights. For the remaining 12 flights, investigation is ongoing. This report summarizes contact tracing results for the first 17 flights. All but two of these came from an affected area in Asia. Forty-one percent (7/17) of the implicated flights were direct flights arriving in Canada from a SARS-affected area in Asia, and seven were connecting flights (via the United States and other cities in Canada) from an affected area in Asia. The remaining flights included two between Canada and the United States. As of 8 May, a total of 338 passengers from the 17 flights have been contacted. Of these passengers, 112 were seated within two rows of the index case, 207 were seated beyond two rows, and seat locations were unknown for the remaining 19. None of the passengers reported symptoms compatible with either the suspect or probable case definition of SARS (Table 2). Additional passenger follow-up was initiated for six flights associated with 20 passengers who were initially classified as SARS cases. These individuals were later excluded (de-listed) on the basis of other causes of their illness. A total of 210 passengers were followed up from these six flights before the individuals were de-listed as cases. Follow-up was terminated once cases had been de-listed. The cases on one of the flights (China Airlines) are described in the next section. |
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SARS-like Illness Associated with Influenza A on In late April, a cluster of 23 individuals with fever and cough in eight households was reported by the Fraser Health Authority of British Columbia; 22 met the national case definition for a suspect case of SARS, and one met the definition for a “person under investigation”. Sixteen of these individuals had travelled to Asia, and the remainder were their household contacts. The first of the travel-related cases were reported on 21 April in two family members whose illness began on 20 April. The remaining 14 had symptom onset between 19 April and 22 April. On April 19, all 16 had travelled on the same China Airlines flight from
New Delhi to Vancouver with a 1-hour layover and change of aircraft in Taipei
airport, Taiwan. Since the stopover location was a WHO SARS-affected area
and the incubation period of the illness was consistent with SARS, these cases
met the national case definition. The flight manifest for the Taipei to Vancouver
flight listed 252 passengers. Passenger contact information was available
from the TCIFs, which had been collected upon landing. A total of 167 passengers
were contacted successfully on 24 and 25 April. As a result of contact tracing,
six additional passengers with one or more symptoms associated with the SARS
prodrome were identified, and local public health authorities were notified
of them for further investigation. However, none was deemed to meet the SARS
case definition of a suspect or probable case. Nasal and throat swabs from nine of the cases were tested for human SARS-coronavirus
(HCoV-SARS) by means of nested RT-PCR (polymerase chain reaction) at the BC
Centre for Disease Control using the National Microbiology Laboratory protocol,
and they were negative. Influenza A virus was isolated in cell culture from
eight individuals, four of whom had been immunized against influenza in the
2002/3 season. The diagnosis of influenza in several of this group of 23 people was in keeping with the clinical syndrome of fever and cough that did not progress to severe respiratory illness. As well, the travel-associated cases were from India, which was not recognized as a SARS-affected area in April 2003. Their infections were likely acquired in India before departure, although some of the travellers may have acquired it during the flight, as nine travel-associated cases sat within three rows of each other on the flight from Taipei to Vancouver, and the median interval from the date of the flight to the date of onset of symptoms was 1 day. No additional people with influenza-like-illness were identified among fellow passengers through the passenger follow-up process. Other features of the cluster consistent with influenza were the high number of secondary cases in the households and the rapid resolution of symptoms after a 48-hour illness. Discussion There is currently no evidence of in-flight transmission of SARS on any flights arriving in Canada from international or domestic ports. Internationally, however, there are some preliminary reports suggesting that in-flight transmission of SARS may have occurred. One of the challenges in establishing a chain of transmission on an aircraft is the difficulty in confidently ruling out transmission before boarding takes place. If a passenger seated close to a case develops SARS, the most likely mode of transmission would be by respiratory droplets. If SARS were detected in a passenger seated at a distance from the index case, other epidemiologic or environmental co-factors would have to be investigated. With the previously documented evidence of transmission of tuberculosis on an aircraft(2,3) and the hypothesized mode of transmission of SARS, the public health measures and infection control precautions recommended by Health Canada and the provincial and territorial ministries of health will continue. However, the extent of the passenger contact tracing will be reviewed by the Public Health Measures Working Group as a result of the findings highlighted in this report. Public health and infection control measures will develop in parallel with the global epidemiology of this disease and will reflect the current state of knowledge about the condition. The TCIFs were employed for the Taipei flights, and this resulted in a more rapid turnaround (within 48 hours) for disseminating passenger contact information. These forms will be further implemented for all incoming flights from Asia and will contain contact information for the 14-day period after passengers disembark in Canada. This will allow rapid and more complete access to passenger contact information when required. References 1. Health Canada. SARS case definitions (updated 4 April 2003). URL: <www.sars.gc.ca>. Accessed 23 April, 2003. 2. Kenyon T, Valway S, Ihle W et al. Transmission of multidrug- 3. CDC. Exposure to passengers and flight crew to Mycobacterium tuberculosis on commercial aircraft, 1992-1995. MMWR 1995;44:137-40. Source: J Flint, MSc, S Burton, BSc, JF Macey, MA, MSc, SL Deeks, MD, MHSc, TWS Tam, MD, A King, MD, MHSc, Immunization and Respiratory Infections Division, Centre for Infectious Disease Prevention and Control (CIDPC), Health Canada; M Bodie-Collins, BScN, Quarantine, Travel and Migration Health, Centre for Emergency Preparedness and Response, CIDPC; M. Naus, MD, MHSc, D. MacDonald, MHSc, C McIntyre, BScN, M Krajden, MD, M Petric, PhD, British Columbia Centre for Disease Control, Vancouver, BC; C Halpert, BScN, L Gustafson, MD, MHSc, A Larder, MD, Fraser Health Authority, BC. * An “affected area” as defined by the World Health Organization is an area in which local chain(s) of transmission of SARS is/are occurring as reported by the national public health authorities. |
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Last Updated: 2003-06-15 |  |
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