Friday, May 21, 2010

BMJ: Flu Transmission Risks On Airplanes




# 4586



Two years ago I flew to Washington D.C. - during flu season - to attend an HHS sponsored pandemic exercise.  


I changed planes in Atlanta coming and going (if you die anywhere in the southeast, no matter what your final destination, you apparently have to go through Atlanta), and spent nearly 10 hours wedged into economy class seating.  


All around me, people were coughing and sneezing. And you guessed it, 48 hours after my return, I was down with a nasty flu-like illness.  

Whether I picked up my virus in the confines of the plane, or at the flu conference (irony being what it is), or simply waiting in the airport terminal is something I’ll never know.  


But I have my suspicions.


Which brings us to a study which appears in the BMJ today, entitled:


BMJ 2010;340:c2424


Transmission of pandemic A/H1N1 2009 influenza on passenger aircraft: retrospective cohort study

Michael G Baker, associate professor1, Craig N Thornley, medical officer of health2, Clair Mills, senior lecturer3, Sally Roberts, microbiologist4, Shanika Perera, medical officer of health2, Julia Peters, medical officer of health2, Anne Kelso, director5, Ian Barr, deputy director5, Nick Wilson, associate professor1

I’ve reproduced portions of the abstract below.  The entire study is available online at the BMJ.

Objectives To assess the risk of transmission of pandemic A/H1N1 2009 influenza (pandemic A/H1N1) from an infected high school group to other passengers on an airline flight and the effectiveness of screening and follow-up of exposed passengers.


Design Retrospective cohort investigation using a questionnaire administered to passengers and laboratory investigation of those with symptoms.


Setting Auckland, New Zealand, with national and international follow-up of passengers.

Participants Passengers seated in the rear section of a Boeing 747-400 long haul flight that arrived on 25 April 2009, including a group of 24 students and teachers and 97 (out of 102) other passengers in the same section of the plane who agreed to be interviewed.

Main outcome measures Laboratory confirmed pandemic A/H1N1 infection in susceptible passengers within 3.2 days of arrival; sensitivity and specificity of influenza symptoms for confirmed infection; and completeness and timeliness of contact tracing.

Results Nine members of the school group were laboratory confirmed cases of pandemic A/H1N1 infection and had symptoms during the flight.

Two other passengers developed confirmed pandemic A/H1N1 infection, 12 and 48 hours after the flight. They reported no other potential sources of infection. Their seating was within two rows of infected passengers, implying a risk of infection of about 3.5% for the 57 passengers in those rows.

All but one of the confirmed pandemic A/H1N1 infected travellers reported cough, but more complex definitions of influenza cases had relatively low sensitivity. Rigorous follow-up by public health workers located 93% of passengers, but only 52% were contacted within 72 hours of arrival.

Conclusions A low but measurable risk of transmission of pandemic A/H1N1 exists during modern commercial air travel. This risk is concentrated close to infected passengers with symptoms. Follow-up and screening of exposed passengers is slow and difficult once they have left the airport.



No real surprises here, of course, except perhaps that fewer people were infected during this flight than one might have expected.  Of course, the usual caveats apply;  this is one study, of one flight, and is specific to the novel H1N1 virus.  


The report summarizes what this research adds to what we know this way:


What is already known on this topic

Respiratory agents may be transmitted during airline travel, although the level of risk is poorly defined for most agents, including influenza
Screening for influenza is difficult because symptoms are variable and may be mild or absent
Very little evidence exists on the best way to follow up arriving travellers who might have been exposed to influenza during a flight

What this study adds

A low but measurable risk of contracting influenza from infected travellers with symptoms exists during a long haul flight and is concentrated within two rows of infected travellers
Screening for people infected with influenza is likely to be more sensitive if it uses the presence of single symptoms such as cough, rather than more complex case definitions
Identification and management of passengers exposed to infections during a flight should be started before passengers leave the airport or board other flights

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