Bay Area leaders were first in the nation to take dramatic action aimed at curbing the spread of the coronavirus.Many thought it was going too far. But in the days and weeks following the shelter-in-place orders here, governors and mayors across the country followed the Bay Area and California’s lead.

The Chronicle examined weekly coronavirus case rates, or how many new cases were reported per 100,000 people, for major U.S. metropolitan areas to see how the Bay Area’s curve compares to the rest of the country.

These charts suggest that early, aggressive physical distancing restrictions led to a “flattened curve” — what one researcher called our “crushed” curve. Compared to hard-hit areas, like New Orleans, New York and Detroit, what we’re seeing in the Bay Area looks less like a curve, and more like a flat line.

Flattening curves

Here’s a look at some metro areas where charts show hopeful signs of a flattening curve and, like the Bay Area, have lower weekly case rates than the U.S. average. Testing capacity has varied greatly across states and regions, but these regions appear to have avoided worst-case scenarios seen elsewhere.

Los Angeles issued its own stay-home order on March 19, the same day Gov. Gavin Newsom imposed the most far-reaching shelter-in-place order in the nation. Los Angeles County has the largest concentration of cases in the state and accounts for nearly half of the deaths in the state so far. But its weekly case rate shows signs of leveling off.

In Texas, the Houston area (Harris County) reported its first two coronavirus cases on March 5, and perhaps benefited from the virus arriving later than in other major urban areas. Houston’s largest event, the Houston Rodeo, was shut down on March 11 after pressure from community members. Harris County Judge Lina Hidalgo issued a stay-home order on March 24, and public health leaders have said the data show a flattening curve.

Washington state is home to the country’s first known coronavirus case, announced on Jan. 21. Gov. Jay Inslee issued a statewide stay-home order on March 23, and law enforcement has been strict to enforce the measure. The Seattle-Tacoma area was the nation’s first epicenter, but Inslee today said case data look hopeful, and announced a road map for reopening Washington’s economy.

The Phoenix area (Maricopa County) reported one of the first U.S. cases in late January, but it wasn’t until March 3 when the next case arrived. The governor’s stay-home order went into effect on March 31, and public health leaders there recently announced the growth rate of hospitalizations was slowing, pointing to a flattened curve.

Hardest-hit areas

Here’s a look at some of the areas that have become epicenters in the pandemic.

New York state’s stay-home order took effect on March 22, not long after the Bay Area’s order. But cases there surged after that date. New York City’s weekly case rate curve hit its high in the week of April 6-12. Since then it appears to have leveled off. The Bay Area’s line is nearly flat in comparison.

An early explanation for why New York City’s case count was so much higher than the Bay Area’s was that the state was testing far more people — at one point three times as many people as California. But, as the crisis there continued to unfold and overwhelmed hospitals, it became clear there was more at work.

One reason is population density. New York City has the country’s highest population density, with more than 27,000 people per square mile. San Francisco is also a dense city, but far less so: It has nearly 19,000 people per square mile. Another factor could be the high reliance on public transportation there.

Michigan reported its first two coronavirus cases on March 10, including one in Wayne County. The curve shows the area’s first significant increase the week of March 16-22, sharply rising to hit its peak the week of March 30-April 5 before a steady decline. Michigan’s stay-at-home order took effect on March 24.

Detroit made headlines for its coronavirus cases, spreading through the city’s police and sheriff’s departments. No one is sure why the Midwest city of just over 670,000 with a population density of fewer than 5,000 people per square mile saw such a significant increase, but Mayor Mike Duggan has pointed to the international airport, and health officials have said the city was not equipped to manage a public health crisis of this scale.

The Orleans Parish curve gradually increased from the date of the first reported case in New Orleans on March 9, then dramatically rose during the week of March 30-April 5. Then came an equally sharp drop-off. The Bay Area line is almost completely flat in comparison.

New Orleans’ population density is about 2,300 people per square mile, but many suspect the rapid escalation of coronavirus cases is tied to Mardi Gras season. Hundreds of thousands of people descended in February, packing the city with celebrations for weeks. New Orleans Mayor LaToya Cantrell issued a stay-home order on March 20, and Louisiana followed on March 23.