Monday, September 26, 2005

Flying to the US: me and what else?

Back in the United States after an eight hour plane ride against 150 km/hr headwinds from Milan's teeming Malpensa airport to a US Eastcoast International airport. In the ten or eleven hours I spent in travel, I came into physical proximity and contact with hundreds of people, including pass port control who took my passport and handed it back to me and then did the same thing for thousands of others from all over the world. I then got on a sealed flying tube, with a few hundred other people from disparate locations, breathed recirculated (but HEPA filtered) air, and was serenaded by the occasional coughs of fellow passengers. I repeated the airport process at in the states, then hopped into a taxicab that will in turn be used by hundreds of other city residents and visitors over the next few days. Viruses now travel at 700 km/hour, even against headwinds.

Our highly interconnected network is the skeleton on which contagious disease now travels. Short of a total shutdown in international travel, there seems little we can do about this. Since people are infective with influenza 12 to 24 hours before symptom onset, the measures used in the SARS outbreak of 2003 are of no avail. SARS is a disease most infective in the latter stages of the disease, when the patient is seriously ill. Hence most of the transmission was to health care workers. Even in the epidemiologically most favorable case of SARS, researchers from the UK's Health Protection Agency publishing in the British Medical Journal, conclude that identifying infected airline travelers is essentially fruitless.
This agency is charged with "investigating options for controlling infectious disease and protecting public health using mathematical simulations," lead investigator Dr. Richard J. Pitman told Reuters Health. "We looked to see if passengers developing a fever during flight would be effective way of preventing importation of SARS or influenza into a country."

Based on the incubation periods for influenza and SARS, the researchers estimated the proportion of individuals with latent disease who would develop symptoms during an international airline flight to the UK. They report their results in BMJ Online First.

"Our findings suggest that approximately 90 percent of cases would not develop symptoms en route and so would get straight through," Pitman said. "The 10 percent that would be picked up would be rapidly replaced by those that got through, so at best there would be only a small delay in onward transmission of the epidemic."

Even for passengers from the Far East or Australia, whose flight durations are the longest, the sensitivity would still be too low to be of benefit, the investigators report. (Reuters Health)
Politicians and health officials will undoubtedly try to restrict travel as a means to safeguard their populatin and appear to be doing something the public feels is "common sense." There is probably jno way to stop them. Just as there is no way to stop this virus once it attains the ability to move efficiently from person to person.