The contours not yet found

WHO issues grim 'iceberg' warning

The lion’s share of the crisis is concentrated in China. Yet the ballooning impact of the virus threatens to take a bite out of first quarter earnings — as well as global growth — as a wide range of multinational companies pull back from the country. On Monday, food chain Restaurant Brands International (QSR) announced that half its Burger King locations there had been shuttered.
Meanwhile, continued delays of operations at factories has increased the U.S. economy’s exposure, though analysts say that effect is contained — for now. Wall Street expects to see the impact in the first quarter, and a bounce-back in Q2 and beyond.
“This is a vulnerability for the U.S. economy,” Calvin Schnure, a former Fed economist and current Nareit senior vice president, told Yahoo Finance Monday.

We know to expect onset of symptoms, may one or two weeks.  But in the initial stages, that two week delay holds a lot of uncertainty about the aggregate effect. Hence the iceberg effect.