A second wave of cities, including Boston, Detroit, New Orleans and Philadelphia, are seeing increases in confirmed coronavirus cases, and could become epicenters for the outbreak if they're not able to bring those cases under control soon.

Why it matters: Whether these cities can prevent their outbreaks from spiraling out of control will be a major test for the U.S.' ability to contain the virus.

New Orleans in particular is nearing a crisis, with hospitals already becoming overwhelmed and supplies of medical safety gear running low, per the NYT.

Orleans Parish has experienced the highest number of deaths per capita of any county in the U.S.

What we're watching: Other cities may have even higher numbers of cases, but just haven't tested enough people to know it.

Between the lines: The U.S. has finite medical resources, including personnel as well as medical supplies like ventilators. The more hotspots we have at one time, the higher the demand for these resources.

The bottom line: State or city borders will not contain the virus. It moved from a market in Wuhan, China to all 5o U.S. states within three months.

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