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Transmission of pandemic (H1N1)
2009 influenza on international flights –
Australia 2009
Ruth Foxwell, Leslee Roberts, Kamalini Lokuge, Paul Kelly
Acknowledgements
Background
•
Emergence of influenza H1N1 variant – Mexico/USA – March 2009
•
WHO pandemic level 5 - 29 April 2009
•
Australian response phases initiated 29 April 2009
•
2.35 million passengers by air – Mexico  164 countries March/April 2008
Background
Respiratory disease transmission on aircraft
• Passengers closer to index case on aircraft are most at risk
• Air filtration in aircraft has been upgraded
• Different disease  different dynamics
Background
Major issues
• Policies for passenger follow-up based on tuberculosis and SARS*
• Limited resources  response priorities
Aim
• Investigate transmission of pandemic influenza (H1N1) 2009 on
international flights arriving in Sydney in May 2009
*WHO technical advice for case management of Influenza (H1N1) in air transport, Geneva 2009
Methods
• Retrospective cohort study on flights arriving Sydney - weekend 23/24 May 2009
• One from country with documented community transmission
• One from country with no documented community transmission
•Data collection
• Surveyed passengers 3 months following flight arrival
• Questions: symptoms ILI, onset date, co-morbidities, movement in-flight,
other potential exposure to ILI; anti-viral prophylaxis, isolation/quarantine,
contact with health professionals following flight
• Triangulated information with national notifications of pandemic (H1N1) 2009
• Ethics approval – DoHA, ANU
Case Definitions
• Influenza-like illness (ILI)
• At least one of cough, sore throat, headache, runny nose, muscle aches,
diarrhoea, lethargy
• Time periods specified for: 7-14 days pre-flight, during flight, 7 days post
flight
•Pandemic (H1N1) 2009
• ILI + Laboratory confirmation
Results – defined population
Total passengers identified from
2 flights
n = 738
Contact details either insufficient
or not available
n = 143 (18%)
Total potential passengers
contacted
n = 603 (82%)
Total surveys returned
n = 319 (response rate = 43%,
participation rate = 53%)
Additional 5 ILIs (23%) and 2 cases
(20%) of pH1N1 identified through
triangulation process
Results – ILI onset dates
Flight 1
Flight arrival in Sydney
Pre-flight ILI infectious in-flight
Results - pH1N1 transmission on aircraft
Disease onset of index case
Proximity to index case
Risk of contracting
pH1N1
Before/during flight
2 + 2 rows
1.4%
Before flight
2 + 2 rows
3.6%
Before flight
2 + 2 seats
7.7%
Timeliness of Public Health Action
• Total passengers followed up by public health officers = 145
• Survey results (from 52 of 145)
• 67% of people contacted by public health ≥ 3 days after flight arrival
• Serial interval of disease = 2.9 days(average)
 Only 33% of passengers followed through in optimal time period
Summary – pandemic (H1N1) 2009
Public Health action for passengers on international flights:
• more timely follow-up required to effectively prevent community spread
from infectious individuals
• travel restrictions for symptomatic individuals may be appropriate
• 2+2 square rather than 2+2 rows may assist in prioritizing contact tracing
for influenza
Results – ILI symptom comparison
Self-reporting of symptoms did not distinguish cause of ILI
•
50% of passengers positive for pandemic (H1N1) 2009 had fever
•
44% of passengers negative for pandemic (H1N1) 2009 had fever
•
20% of passengers with ILI but not tested for pandemic (H1N1) 2009 had fever
Number of different symptoms did not distinguish cause of ILI
•
Two or less symptoms not including fever reported for:
• 38% of passengers positive for pandemic (H1N1) 2009
• 44% of passengers negative for pandemic (H1N1) 2009
• 66% of passengers with ILI but not tested for pandemic (H1N1) 2009