ROME—The coronavirus has killed more people in Italy than in China over the past week. Doctors are warning that a shortage of beds to treat the severely ill could push the Italian death toll higher still.

In less than three weeks, Italy has gone from having just three coronavirus cases to the biggest outbreak after China. And the data point to a troubling trend: Those infected in Italy appear more likely to die.

Incomplete data, especially on total infections, makes mortality rates uncertain at this point in the global epidemic. But Italy’s high number of deaths has health experts worried. Many say that, if Italians are more likely to die, then demographics are probably a big part of the reason.

By Monday, Italy’s total confirmed infections reached 9,172 of whom 463, or 5%, had died. In Lombardy, the worst-affected region, the death rate is 6%. Globally, about 3.5% out of 109,578 people with confirmed cases have died, according to the latest data from the World Health Organization. Many experts say the real mortality rate may well be lower, because many infection cases aren’t known.

“From a biological point of view, it’s inexplicable,” said Giorgio Palù, a virologist at the University of Padua. “The only thing we know for sure is that Italy’s population is one of the oldest in the world.”