Transmission of pandemic (H1N1) 2009 influenza on international flights –

Australia 2009

Acknowledgements

Ruth Foxwell, Leslee Roberts, Kamalini Lokuge, Paul Kelly

• 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

• Passengers closer to index case on aircraft are most at risk

• Air filtration in aircraft has been upgraded

• Different disease different dynamics

Respiratory disease transmission on aircraft

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

Background

• 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

Methods

• 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

Case Definitions

Total passengers identified from 2 flights

n = 738

Total potential passengers contacted

n = 603 (82%)

Contact details either insufficient or not available

n = 143 (18%)

Total surveys returned

n = 319 (response rate = 43%, participation rate = 53%)

Results – defined population

Additional 5 ILIs (23%) and 2 cases (20%) of pH1N1 identified through

triangulation process

Flight 1

Flight arrival in Sydney

Pre-flight ILI - infectious in-flight

Results – ILI onset dates

Results - pH1N1 transmission on aircraft

Disease onset of index case Proximity to index caseRisk 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