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FRIDAY, October 5, 2018 – A new study suggests that large cities with large numbers of people commuting daily tend to have longer and more severe flu seasons.
The researchers found that the flu season in a city would last longer if the city's population increased and the workplaces became more focused, said lead researcher Benjamin Dalziel, a population biologist at the University of Ottawa. Oregon State University.
"Big cities have more organized movement patterns, and these patterns connect pockets of high population density," Dalziel said. "We found that this structure influences the spread of flu at different times of the year."
Armed with this knowledge, public health experts could better predict the impact of an influenza season by examining early infection rates in large cities, said co-investigator Cecile Viboud. She is a staff member of the Fogarty International Center of the US National Institutes of Health.
"If we could strengthen surveillance in these cities, we would have an earlier window on the severity of outbreaks and we could use that data to help predict epidemics at the regional or national level," Viboud said.
Such an advantage could be crucial as US health authorities announced last week that flu had killed about 80,000 Americans during last winter's influenza season, making it the deadliest season ever since. forty years old.
A particularly virulent influenza strain, H3N2, has ravaged the country during the 2017-2018 season, causing a record number of deaths and hospitalizations, reported the US Center for Disease Control and Prevention.
The flu vaccination rate also dropped last year, officials said, leaving more people vulnerable to the virus and making influenza vaccines even more imperative in this influenza season.
In general, the flu season is experiencing peaks during the winter due to the drop in humidity, Dalziel said.
"The flu is passed from person to person by virulent moisture droplets that an infected person exhales, coughs or sneezes.This creates what you may consider as a cloud of risk moving around." an infected person, "said Dalziel.
During the winter, the humidity decreases "and thus, the virus remains viable longer in the air, which effectively widens the cloud of risk," he explained.
Researchers have found, however, that in large cities, where people are stormed, dry weather in winter is less important.
"If an infected person is sitting right next to you, the specific moisture content does not matter," said Dalziel. "It helps the virus to find a host even when the weather is not optimal."
Dalziel and his colleagues combined six years of influenza case data with census data showing where people live and work in 603 different cities across the United States.
Investigators have found that in large metropolitan areas, influenza cases are more prevalent, including at the beginning and at the end of the season when the weather is not conducive to transmission. New York and Miami are examples of cities where the flu season is longer, said the study's authors.
On the other hand, small towns tend to have short, well-grouped influenza seasons around the usual peak in winter. Atlanta and Nashville are examples, where the flu hits for a more concentrated period.
The researchers noted that the risk of contracting influenza remains the same in all cities.
Viboud said, "This does not show that some cities are safer than others against the flu, it shows the relative difference in the timing of the cases."
The data shows that public health officials must take into account the structure of their metropolitan area when planning each influenza season, the researchers suggested.
Large cities with longer influenza seasons will have to prepare for cases to start appearing earlier, for example.
"On the other hand," said Viboud, "in small towns, a more intense epidemic could overburden the health care system, making it particularly difficult to cope with epidemics."
The study shows how the rise of megacities could make a new influenza pandemic more likely, said Dr. Amesh Adalja, senior researcher at the Johns Hopkins Center for Health Security in Baltimore. He was not involved in the new study.
"Influenza in big cities behaves differently with longer transmission chains, longer seasons, and less vulnerability to changes in humidity compared to smaller cities," said Adalja.
"This study underscores the need to intensify pandemic preparedness efforts in the world's largest cities, as they may well be the main drivers of the threatening influenza pandemic," he added.
The study was published on October 5 in the journal Science.
More information
US Centers for Disease Control and Prevention have more about influenza.
Copyright © 2018 HealthDay. All rights reserved.
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