# 5244
In March of 2008 I flew from Orlando to Washington D.C. (changing planes in Atlanta) to attend an HHS sponsored Flu conference. As this was prime cold & flu season, passengers on all 4 legs of this trip were sneezing and coughing around me.
And as is appropriate for returning from an influenza conference, two days later I came down with the the `flu’ (actually an Influenza-like Illness).
I’ve no idea exactly where I picked up this nasty viral hitchhiker. It could have been aboard the planes, or it may well have been at the conference (a lot of conversational huddles and handshaking going on), or at the hotel, or during the several hours of waiting in the airport terminals.
Surprisingly, during the 2009 influenza pandemic I made two similar airline trips (to Washington D.C. & Minneapolis) to flu conferences, and managed to evade illness both times.
Go figure.
Which brings us to a study that recently appeared in BMC Infectious Diseases, that looked at the incidence of ARI (Acute Respiratory Infection) presenting within 5 days of train or tram travel in the UK.
First a link, and some excerpts from the abstract, then some discussion on why this is interesting on several levels.
Is public transport a risk factor for acute respiratory infection?
BMC Infectious Diseases 2011, 11:16 doi:10.1186/1471-2334-11-16
Joy Troko, Puja Myles, Jack Gibson, Ahmed Hashim, Joanne Enstone, Susan Kingdon, Chris Packham, Shahid Amin, Andrew Hayward, Jonathan Nguyen-Van-Tam
ABSTRACT
Background:
The relationship between public transport use and acquisition of acute respiratory infection (ARI) is not well understood but potentially important during epidemics and pandemics.
Methods:
A case-control study performed during the 2008/09 influenza season. Cases (n=72) consulted a General Practitioner with ARI, and controls with another non-respiratory acute condition (n=66). Data were obtained on bus or tram usage in the five days preceding illness onset (cases) or the five days before consultation (controls) alongside demographic details. Multiple logistic regression modelling was used to investigate the association between bus or tram use and ARI, adjusting for potential confounders.
Results:
Recent bus or tram use within five days of symptom onset was associated with an almost six-fold increased risk of consulting for ARI (adjusted OR=5.94 95% CI 1.33- 26.5).
The risk of ARI appeared to be modified according to the degree of habitual bus and tram use, but this was not statistically significant (1-3 times/week: adjusted OR=0.54 (95% CI 0.15-1.95; >3 times/week: 0.37 (95% CI 0.13-1.06).
Conclusions:
We found a statistically significant association between ARI and bus or tram use in the five days before symptom onset. The risk appeared greatest among occasional bus or tram users, but this trend was not statistically significant. However, these data are plausible in relation to the greater likelihood of developing protective antibodies to common respiratory viruses if repeatedly exposed. The findings have differing implications for the control of seasonal acute respiratory infections and for pandemic influenza.
The complete article is available as a provisional PDF. The fully formatted PDF and HTML versions are in production.
One of the difficult questions that public health officials must contend with are what precautions they should recommend to the public during an epidemic.
As we saw early in the 2009 pandemic, before the risks of the newly emerged H1N1 virus were well established, the CDC was quick to recommend the closing of schools when cases appeared, and a 7-day period of home isolation for infected cases.
Once it became apparent that the virus wasn’t as virulent as first feared - in order to reduce their impact on society - many of those recommendations were relaxed.
In order to make these determinations, much depends on the type and severity of an outbreak, its rate of spread (R0), and the manner in which it is transmitted (ie. aerosolized, large droplet, fomites, orofecal route).
And those are factors that must be established for every novel illness.
Because, if you’ve seen one pandemic . . . you’ve seen one pandemic.
The authors of this BMC study point out that the UK pandemic plan is disrupt the continuity of society as little as possible during a pandemic.
The current UK National Framework for Pandemic Influenza states that during a pandemic, domestic travel should continue to operate normally but users should adopt good hygiene measures, stagger journeys where possible to reduce overcrowding; and stay at home altogether if symptomatic with pandemic influenza [1].
This advice reflects the need to maintain, as far as possible, business continuity and near normal functioning of society, but acknowledges that some data exist about the transmission of influenza on board public transport, notably commercial airliners [2].
Not every country is on the same page with this.
In Japan - prior to the 2009 pandemic outbreak - we saw a different tactic being tested; the enforced separation (by 1 to 2 meters) of passengers on public transportation (see Japan: Social Distancing Test On Commuter Trains).
Granted, these Japanese drills were based on an extremely virulent `bird flu’ type virus.
Understanding how readily viruses may be transmitted in an enclosed environment (like a train, plane, or tram) can help pandemic planners better make crucial decisions.
Interestingly, those who were frequent users of public transportation were slightly less likely to consult their GP for an ARI during this study period, than those who were only occasional users.
Since this study was conducted in the month of December, it is possible that more frequent users of public transportation had already been exposed to the `flu’ earlier in the season, although the authors suggest further study on this finding is warranted.
While a six-fold increase in ARI consultations among recent public transport users is compelling, these results must be accepted with caution.
Among other factors: the size of this observational study was small, it was conducted in a single location (Nottingham, UK), and it was conducted during a normal flu season, not a pandemic.
The authors conclude that while the use of public transport is associated with a significant individual risk for acquiring an ARI during the winter, the UK’s current pandemic policy on public transportation during an epidemic is sound.
The findings support current public advice to exercise good respiratory hygiene and existing pandemic guidance to refrain from making unnecessary journeys by public transport when symptomatic.
The findings do not support the effectiveness of suspending mass urban transport systems as a pandemic countermeasure aimed at reducing or slowing population spread because, whatever the relevance of public transport is to individual-level risk, household exposure most likely poses a greater threat [3].
Coincidentally, we are once again about to witness the busiest travel period of the year; Chunyun, or the Spring Festival Travel Season (of which Chinese New Years is a central part)
It is, quite rightfully, billed as the largest annual migration of humans on the planet. Chunyun begins about 15 days before the Lunar New Year and runs for about 40 days total.
This year, the Lunar New year falls on February 3rd, and with it comes a cultural ethic for millions who have moved to the big cities to return home to visit with their families for a few days.
During this time, it has been estimated that well over 2 billion passenger journeys are taken, mostly by bus and train, across Asia.
With H1N1 still making the rounds, epidemiologists will no doubt be watching to see if a post-Chunyun increase in influenza cases is observed during February across Asia.
