Study Reveals How an Influenza Epidemic Travels
Geography, commuting patterns affect spread, suggest better response
Washington – The way commuters travel to work every day is a key factor in the transmission of a flu virus, according to a study announced April 19 by the Fogarty International Center (FIC) of the National Institutes of Health (NIH).
The research, based on more than 30 years of data from annual influenza outbreaks, could help in making decisions on community health responses for future disease patterns.
“We can correlate interstate spread with population size, commuting and virus type,” said Dr. Mark Miller, FIC’s associate director for research. “We synthesize long-term data about disease incidence and human movements using [mathematical] models.”
What FIC found is that disease spreads more rapidly across the country if it first is introduced in a state that has strong connections with other parts of the world, and many workers flow back and forth across its borders.
California – with its connections to the Asia-Pacific community, huge economy and population – is such a state. Wyoming – a landlocked agricultural state with a fraction of California’s population – is not.
Earlier studies have emphasized the role that children can play in influenza transmission, but this study takes a different approach, suggesting that adults primarily are responsible for the regional movements of infection because travel across such distances is routine in many adult lives.
An April 19 NIH press release on the new research cautions about applying this model to the potential transmission of serious pandemic influenza.
A highly virulent influenza strain, to which no one has immunity, may not move the same way as the common forms of flu, which were the basis of the FIC study.
Still, the researchers predict that pandemic disease introduced in California could spread to all 50 U.S. states in four weeks or less. A disease introduced into a less-connected state might take up to seven weeks to spread across the country.
The next step in this work will be to study how specific actions – closing schools or workplaces or restricting travel might – slow down disease transmission.
Identifying the most effective control strategies might be an important way to save lives in a serious pandemic influenza.
BIRD FLU UPDATE
The latest work from NIH comes at a time when international health authorities warn about the potential outbreak of a global influenza pandemic due to a highly pathogenic form of avian influenza that started spreading through Asia in late 2003.
The disease has affected almost 200 people in nine countries, with 110 deaths.
The latest fatality reported by the World Health Organization (WHO) April 19 comes from Indonesia. A 24-year-old man died from exposure to the H5N1 virus in early April. Indonesia has suffered the second-largest number of human disease cases with 32.
Vietnam has experienced the most human cases of avian influenza – 93 cases of disease and 42 lives lost.
WHO also reports a new human case in China. A 21-year-old male developed symptoms April 1 and is now hospitalized in critical condition.
How this migrant worker in Hubei province could have exposed to the disease is being investigated. No poultry outbreaks have been reported in that region since November 2005.