The New York Times

Enthusiasm for Elena Ferrante’s novels runs so high that it has been described in epidemiological terms, making the phenomenon sound almost like an infectious disease.

And judging by the latest sales figures from her publisher, so-called Ferrante fever appears to have spread around the world.

Her Neapolitan novels — a four-book series that follows two female friends living on the outskirts of Naples from childhood through adulthood — have sold about 5.5 million copies worldwide, according to Europa Editions. Publication rights have sold in nearly 50 countries, including Estonia, Turkey and Indonesia.

In North America, the four novels have sold nearly two million copies — making them a rare commercial blockbuster from an anonymous author in translation. They have sold more than a million copies in Ms. Ferrante’s native Italy, and have climbed the best-seller lists in France, Germany and Britain. Worldwide sales in English now top three million.

Part of the mystique surrounding Ms. Ferrante stems from her enigmatic persona. She writes under a pseudonym, and is fiercely protective of her privacy. Theories about her identity have been frequently floated and debunked.

This fall, the Italian investigative journalist Claudio Gatti published a forensically detailed report in The New York Review of Books arguing that the Rome-based translator Anita Raja was behind the Ferrante novels. The revelation was met with outrage from Ferrante fans, who said the author’s privacy had been violated. Devoted readers fretted that Ms. Ferrante would never write again.

Her publisher declined to confirm or deny the report. “To us it remains simply more speculation about her identity of the kind that we have always been uninterested in either denying or confirming,” a spokeswoman for Europa said in an email.

If anything, though, the revelation and the ensuing furor have only heightened interest in her work. This November, Europa released an English translation of “Frantumaglia,” a collection of interviews, correspondence with editors and other ephemera from her career. People began picking over the discrepancies between her self-described background as the daughter of a Neapolitan seamstress, and the conflicting portrait that Mr. Gatti put forth.

Given the choice between Mr. Gatti’s version and the myth of Elena Ferrante, most of her readers seem to prefer the myth.

“I had no desire at all at the end to know who the real Ferrante is,” the British novelist Lisa Appignanesi wrote in a glowing review of “Frantumaglia” in The Guardian. “I feel I already know.”