boyfriend was beaten during a six-hour abduction aboard a minibus in the famed beach district of Copacabana.
The case grabbed international headlines and drew comparisons to last December's similar gang rape of a young Indian woman in New Delhi, which led to a 25% fall in tourist arrivals.
"Nobody expects to be assaulted in Disneyland. Copacabana is our Disneyland. It rings alarm bells," Alfredo Lopes, president of the Rio Hotels Association, said, according to press reports.
The rape came as Rio pressed on with a campaign to shake off a reputation for violent crime, with a succession of police operations to take control of dozens of favelas, slums once under the sway of drug traffickers or militias.
The Marvelous City, as Rio is known, is to host the Confederations Cup, a dry run for next year's World Cup, in June.
And a month later, the city is to welcome Pope Francis and some 2.5 million people for World Youth Day.
The female American student and her French boyfriend boarded a minibus at around midnight on Saturday in Copacabana headed to Lapa, a trendy area home to popular bars and dance clubs.
Two men who also boarded the minibus ordered the rest of the passengers to get off and handcuffed their victims.
They then proceeded to beat the young man with a metal bar and rape the young woman as they rode around the city, Rio's tourist police (DEAT) said.
After seeing photographs of two of the detained suspects, a young Brazilian woman who was raped on March 23, also in a minibus, identified them as her assailants, DEAT added.
The driver of the minibus may also have taken part in the rape.
The G1 news website said the Frenchman suffered a severe eye injury and a fractured face while the American's nose was broken during the assault.
Minibuses are part of Rio's transportation network and, in a city of six million inhabitants, are considered a convenient means of getting around.
Although the case sparked deep revulsion in Brazil, officials were quick to insist it was an isolated incident.
"It is horrendous, but this is not a routine occurrence in Rio," Rio state security secretary Jose Mariano Beltrame told AFP. "It is unfair to present it as such."
"Such a brutal rape is very spectacular but is generally quickly forgotten. It is not (as) common in Brazil as it is in India," said Augusto Rodrigues, a crime expert at the State University of Rio de Janeiro.
"It is an isolated incident which must not be used as a parameter to measure violence," said Michel Misse, of the Federal University of Rio de Janeiro.
Asked about a 24 percent rise in rapes in Rio from 2011 to 2012 (from 4,871 to 6,029), both experts attributed it to increased reporting by women to special police units set up to assist sex assault victims.
"Before they were ashamed to report such crimes in police stations run by men," Misse said.
The experts insist that, broadly speaking, security has never been better in Rio and in Brazil in general, even though the crime rate remains high compared to European or US norms.
In 2010, the murder rate in Brazil was 21 per 100,000 inhabitants, the 11th highest in the world, compared to 26.7 in 2000, according to the United Nations.
In Sao Paulo, Brazil's most populous city, the murder rate fell to 13 per 100,000 residents, "a reasonable rate," from nearly 60 per 100,000 in 2000, Misse said.
On Monday eight military police officers were arrested in Sao Paulo as part of a probe into the killing of two youths after their fatal shooting was shown on television.
A day earlier, Globo TV had aired security camera footage showing two men on a motorcycle approach three youngsters in the popular Bras neighborhood in Sao Paulo and shoot two of them.
Images from another camera show that, at the time of the executions, a military police vehicle was parked about 50 meters (yards) from where the victims were.