Data: CSSE Johns Hopkins University, National Center of Health Statistics, U.S. Census Bureau; Chart: Andrew Witherspoon/AxiosThis wave of coronavirus infections is hitting rural areas especially hard. While big cities have more total cases, rural areas are seeing more cases per capita — and they're at greater risk of running out of hospital capacity as cases pile up.Why it matters: What started as an urban problem in the spring is now everyone's problem.Between the lines: Rural communities in the U.S. have more vulnerable health care systems and more vulnerable populations. Many are on the verge of becoming overwhelmed by coronavirus patients as caseloads continue to grow. Coronavirus patients are occupying the highest portions of hospital beds in Midwestern and Mountain West states. And hospitalizations tend to trail cases by a few weeks, meaning the burden on hospitals is only likely to get worse.As the outbreak also continues to grow in big cities, rural systems may end up with nowhere to send patients after they run out of room to treat them.Health care workers are less likely to be able to temporarily relocate to hotspots, as they'll be needed in their own communities. Zoom in: Childress County, Texas, has the highest per capita case rate in the country, with 91 cases per day in a county of just over 7,200 people — or 1,265.3 cases per 100,000 people.The bottom line: "We have legitimate reason to be very, very concerned about our health system at a national level," Lauren Sauer, an assistant professor of emergency medicine at Johns Hopkins University, told NPR.