As of Friday, she was staring at a spreadsheet with 187 infected at Harper’s Restaurant and Brew Pub.

“The tables were six feet apart, but no one stayed there,” she said. “The DJ was playing music so people were shouting, the dance floor started to get crowded. We had flattened the curve and then boom.”

The East Lansing case is what’s known as a superspreading event — possibly the largest so far in the United States among the general public. Many scientists say such infection bursts — probably sparked by a single, highly infectious individual who may show no signs of illness and unwittingly share an enclosed space with many others — are driving the pandemic. They worry these cases, rather than routine transmission between one infected person and, say, two or three close contacts, are propelling case counts out of control.

More than 1,000 suspected clusters — ranging from the single digits to thousands — have been logged in a database compiled by a coder in the Netherlands. A megachurch in South Korea. A political rally in Madrid. An engagement party in Rio de Janeiro. Nearly all took place indoors, or in indoor-outdoor spaces.