October 2006
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Research
Flu control: a public health lesson
In recent years, flu has tended to peak around February 17 (blue line). But international flight volume (in red) plummeted after the 9/11 attacks, delaying the peak until March 2. Air travel restrictions after the attacks of September 11, 2001, may have had an unexpected healthful effect: They slowed the spread of flu, delaying the 2001-2002 U.S. flu season by nearly two weeks. An analysis by John Brownstein, PhD, and Ken Mandl MD, MPH, of the Children's Hospital Informatics Program, suggests that limiting air travel could buy critical time during a flu pandemic.
"For the first time, we've been able to show that airlines help spread the flu, and that you can impact its spread by slowing down air travel," Brownstein says.
While other researchers have used simulation to study air travel's effect on flu, Brownstein and Mandl used real data from the Centers for Disease Control and Prevention. Analyzing nine consecutive flu seasons beginning with 1996-1997, they found that flu consistently peaked on or around February 17 during the first five seasons. But in 2001-2002, it didn't peak until March 2. In the following years, the peaks occurred in the usual February time frame.
"At first we thought there was a problem with the data," says Mandl. "But then we realized we were seeing the shadow of September 11 cast upon the influenza season."
During the 2001-2002 flu season, it took 53 days for flu to spread across the United States, compared with the usual 33-day average, the researchers found. In contrast, in France, where flight restrictions were not imposed, there was no post-September 11 delay in flu activity.
Brownstein and Mandl also showed that domestic airline volume during November is an especially strong predictor of how flu spreads, confirming suspicions that Thanksgiving travel helps spread new flu strains across the country. For international flights, passenger volume in September was the strongest predictor of flu spread, suggesting that September is when foreign flu strains are introduced to the United States.
Given fears about bird flu, both the U.S. government and the World Health Organization are now considering flight restrictions should we have a flu pandemic. The researchers hope their findings, published September 12 in the online journal PLoS Medicine, will influence their decisions.
An all-nighter drug?
People who need to stay awake—soldiers, pilots, truckers, students, doctors, parents of newborns—might someday benefit from drugs that prevent nitric oxide gas from building up in the brain. Research conducted jointly at Children's Hospital Boston and the University of Helsinki in Finland finds that accumulation of nitric oxide, which is produced naturally in the basal forebrain, is both necessary and sufficient to produce sleep."This new understanding might provide a basis for completely new drugs to prevent excessive sleepiness or to promote sleep," says Paul Rosenberg, MD, PhD, a researcher in the Neurobiology Program at Children's who also sees patients at the hospital's Center for Pediatric Sleep Disorders.
Rosenberg and his Finnish collaborators found that nitric oxide production in the basal forebrain increased by 50 to 150 percent in rats that were mildly sleep-deprived. When agents inhibiting nitric oxide production were injected into their basal forebrains, the rats were able to stay awake. The same was true when the researchers injected a compound that removed nitric oxide from their brains.
On the flip side, when rats on a normal sleep-wake cycle received an agent that boosts nitric oxide levels, the rats fell into a sleep much like the "recovery" sleep that occurs after prolonged wakefulness.
The results tie in with previous research showing that adenosine accumulation in the brain triggers sleep. In 2000, Rosenberg showed that nitric oxide stimulates adenosine's release. The new studies revealed that nitric oxide inhibitors also prevent adenosine accumulation, while agents boosting nitric oxide production also boost adenosine levels.
The findings appeared in the August 18 issue of the Journal of Neurochemistry and the September 5 issue of the European Journal of Neuroscience.
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