2. Flu hits smaller cities harder
Smaller cities — especially those that aren't very humid — tend to have higher flu epidemic intensity than larger cities, scientists say in a new study published in Science on Thursday. Conversely, large cities with extensive transportation systems tend to have longer, more consistent flu seasons, they found, Eileen Drage O'Reilly reports.
Why it matters: As seen last season, flu epidemics can be quite deadly and their intensity is caused by several factors. When smaller cities, like Nashville and Atlanta shown above, experience sharp spikes in flu cases, there is a bigger burden placed on their health care systems, which may call for implementing "surge capacity" in treatment centers, study author Cecile Viboud said.
Background: Seasonal flu epidemics are complicated, and there's growing evidence that "outside factors" may play a role.
What they did: The researchers looked at 6 years of medical claims for weekly incidence of influenza-like illnesses in 603 regions of the U.S. They compared the levels of such illnesses with factors believed to play a role in transmission: population size, humidity, residential crowding, median household, vaccination coverage and income.
What they found:
- Epidemic intensity (or the peak level of infections) is actually higher in cities with smaller populations, less residential crowding and lower incomes, co-author Benjamin Dalziel tells Axios.
- Densely populated, upper-income, larger cities, on the other hand, showed lower epidemic intensity despite being a "transmission hub."
- In large cities, what impacts epidemic intensity is the organization of movement patterns and the "hot pockets" of infection.
- In small cities, humidity plays a bigger role, Dalziel says, because the virus droplets have more time to infect people.
Outside perspective: Outside researchers say this is an interesting look at possible factors affecting flu intensity and should inspire further research.
Katelyn Gostic, disease ecologist and Ph.D. candidate at UCLA, tells Axios the study shows interesting patterns.
"[T]his study shows that influenza epidemics in smaller cities burn hot and fast, while epidemics in big megacities burn at more of a year-round smolder," she said.
What's next: Jacco Wallinga, of the National Institute for Public Health and the Environment in the Netherlands, writes in Science Perspectives:
"This is important for policy-makers because it indicates that metropolitan areas should focus on reducing influenza spread, whereas small towns should focus on reducing harm."