Not a chance that the Italian case numbers are close to accurate. They must have some 5 times the numbers of cases reported. I live in Norway, and people coming home from Winter holiday in Italy are infected left and right. Not a chance that they all happened to meet one of the 5000 sick in a country of millions. So the "serious case or deadly case" rate, purely objectively and not related to a specific country, is lower than you would infer from these numbers. My guesswork based on published data puts it at 0.1%-0.4%, assuming good treatment options, with those above 60 or with pre-existing conditions at the most risk. (Cardiovascular disease, pulmonary disease, immunocompromised, diabetes, hypertension). The latter is a scary wildcard for the US, USA has a high incidence of obesity which often comes along with these.
That said, I second that this is likely to impact the macro economy. The testing rate of the US is worse than Italy's, based on the number of dead there so far. The US has much more cases than officially reported, and the number of cases is currently doubling every 4-6 days.