After analyzing data from 2002 to 2008 on flu cases in 603 cities in the United States, researchers have determined that a city’s size and structure plays a significant role in how flu epidemics occur and expand.
Researchers from Oregon State University, University of Cambridge, Pennsylvania State University and Princeton University have found that large, densely populated cities experience a steady accumulation of cases throughout ‘flu season’. On the other hand, smaller, less crowded cities experience an intense surge of flu cases in winter.
Factors besides population density also come into play. The report, published in the international journal Science, found that air conditions seem to be the main driver in smaller cities. Dry air helps flu viruses survive longer and go on to infect more people. This is why less populated areas experience a surge in flu cases during the dry winter months.
In concentrated areas, however, there is never a dearth of new hosts for the virus to infect, allowing it to spread steadily without having to wait for the dry season. This also explains why some cities face more intense flu epidemics than others year after year. The evolution of individual strains of the virus is also a significant factor.
Study co-author and population biologist Benjamin Dalziel of Oregon State University has said that understanding how the urban environment impacts the spread of infectious disease could help predict epidemics and control outbreaks when they occur.
According to the Centre for Disease Control and Prevention (CDC) — the US’s leading national public health institute — 80,000 Americans died from flu and flu related complications during the 2017-2018 flu season. This was the greatest number of influenza related fatalities recorded in over a decade.
Not only could research like this help prevent outbreaks from reaching pandemic levels, it could also help in designing smarter cities that make it harder for viruses to infect a large number of hosts.