This story was originally published in October 2015 and has been updated.

(CNN) Sex workers do business in every state, but only in Nevada is prostitution legalized, specifically in brothels.

Nevada's bordellos gained attention after former NBA and reality TV star Lamar Odom collapsed inside one, the Love Ranch in Crystal, about 60 miles outside Las Vegas, in October 2015.

Here are a few things to know about Nevada's sex-trade establishments.

Kris Jenner, left, and Kim Kardashian leave Sunrise Hospital & Medical Center in Las Vegas where Odom was being treated on Wednesday, October 14.

Kris Jenner, left, and Kim Kardashian leave Sunrise Hospital & Medical Center in Las Vegas where Odom was being treated on Wednesday, October 14.

Odom plays for Spanish basketball club Laboral Kutxa during a Euroleague game in Vitoria, Spain, in February 2014.

Odom plays for Spanish basketball club Laboral Kutxa during a Euroleague game in Vitoria, Spain, in February 2014.

From left, Rob Kardashian, Odom, Khloe Kardashian, Kourtney Kardashian and Kim Kardashian pose for photographers during an event in Los Angeles in April 2011. Odom was married to Khloe, and he was featured in the reality show "Keeping Up With the Kardashians" as well as the couple's own reality show, "Khloe & Lamar," which lasted two seasons.

From left, Rob Kardashian, Odom, Khloe Kardashian, Kourtney Kardashian and Kim Kardashian pose for photographers during an event in Los Angeles in April 2011. Odom was married to Khloe, and he was featured in the reality show "Keeping Up With the Kardashians" as well as the couple's own reality show, "Khloe & Lamar," which lasted two seasons.

Odom receives the Sixth Man of the Year Award from Lakers general manager Mitch Kupchak in April 2011. The award honors the NBA's best player in a reserve role.

Odom receives the Sixth Man of the Year Award from Lakers general manager Mitch Kupchak in April 2011. The award honors the NBA's best player in a reserve role.

Chauncey Billups, left, and Odom hold a trophy after the U.S. team won at the 2010 World Championships.

Chauncey Billups, left, and Odom hold a trophy after the U.S. team won at the 2010 World Championships.

Odom hoists the Larry O'Brien Trophy while riding in the Lakers' victory parade in June 2010. The Lakers defeated the Boston Celtics for a second straight championship.

Odom hoists the Larry O'Brien Trophy while riding in the Lakers' victory parade in June 2010. The Lakers defeated the Boston Celtics for a second straight championship.

Odom sits next to the Larry O'Brien Trophy during the Lakers' flight back to Los Angeles in June 2009. The Lakers defeated the Orlando Magic for the NBA championship.

Odom sits next to the Larry O'Brien Trophy during the Lakers' flight back to Los Angeles in June 2009. The Lakers defeated the Orlando Magic for the NBA championship.

Odom speaks to the press as a Los Angeles Laker in October 2005.

Odom speaks to the press as a Los Angeles Laker in October 2005.

Odom plays for the Miami Heat in December 2003.

Odom plays for the Miami Heat in December 2003.

Odom huddles with his Clippers teammates before a game in December 2002.

Odom huddles with his Clippers teammates before a game in December 2002.

Odom goes for a dunk during a game in 2000.

Odom goes for a dunk during a game in 2000.

Odom shakes hands with NBA Commissioner David Stern during the 1999 NBA Draft. Odom was drafted by the Los Angeles Clippers.

Odom shakes hands with NBA Commissioner David Stern during the 1999 NBA Draft. Odom was drafted by the Los Angeles Clippers.

Odom laughs during a game with the University of Rhode Island in November 1998.

Odom laughs during a game with the University of Rhode Island in November 1998.

Lamar Odom dribbles the ball during an NBA game against the Denver Nuggets in November 2010. Odom, who won two championships during his career and later married reality TV star Khloe Kardashian, was hospitalized Tuesday, October 13, after he was found unconscious at a brothel in Nevada. On October 19, Odom was transferred to a Los Angeles hospital where he is reportedly breathing on his own.

Lamar Odom dribbles the ball during an NBA game against the Denver Nuggets in November 2010. Odom, who won two championships during his career and later married reality TV star Khloe Kardashian, was hospitalized Tuesday, October 13, after he was found unconscious at a brothel in Nevada. On October 19, Odom was transferred to a Los Angeles hospital where he is reportedly breathing on his own.

Brothels not legal in big cities

That means no legal prostitution in Clark County, where Las Vegas is. County law prohibits brothels in Washoe County, home to Reno, and several other counties.

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Nevada provides a tolerant atmosphere toward prostitution, and though illegal today in Las Vegas, the city remains renowned for its ongoing sex trade -- as well as its slogan of "What happens in Vegas, stays in Vegas."

Nineteen brothels operate in Nevada, down from 36 in the peak years of the mid-1980s, according to the Las Vegas Review-Journal. The brothels are open for business in eight counties, though four more counties allow brothels but don't have any, the newspaper said.

There are three kinds: the small frontier brothel along remote stretches of highway, the small brothel in an isolated small town, and the large, urban-like bordellos outside Las Vegas, Reno, Lake Tahoe and Carson City, according to a University of Nevada, Las Vegas, study.

Testing aims to prevent STIs

The state board of health requires sex workers to undergo testing for sexually transmitted infections.

Brothels cannot employ prostitutes until test results "do not show the presence of infectious syphilis, gonorrhea, chlamydia trachomatis or infection with the human immunodeficiency virus (HIV)," the state regulations say.

Monthly blood testing is required for HIV and syphilis.

Sex workers must also require patrons to use condoms.

How the deal for sex is made

UNLV sociologists Barb Brents and Kate Hausbeck described how the brothels operate in a 2006 paper.

In general, initial contact takes place in a central parlor. Customers approach women from a lineup or at the brothel's bar.

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The price for sex is negotiated "behind closed doors in the individual prostitute's room," the sociologists said.

Female sex workers reported they can refuse clients, and one common way is setting too high a price.

"The more elite prostitutes had the most control over who they service. Some reported that they only dealt with regulars," the UNLV report said.

Brothel stars in HBO reality show

One brothel had its own HBO series, and it featured Dennis Hof, also the owner of the brothel where Odom fell ill and became unconscious.

Nevada's Moonlite Bunny Ranch outside Reno has been the subject of the series "Cathouse." HBO said the series began after the brothel was featured in two specials in 2002 and 2003 that became the network's "highest-rated adult documentaries."

The episodes utilize "hidden cameras in the brothel's 'party rooms' to eavesdrop on customers and 'working girls' before, during and after sex," HBO's website said.

Brothels' advertising is limited

Nevada brothels can't advertise in any city or county that doesn't allow prostitution.

Arguing the law violated the First Amendment, the ACLU won in a federal trial court, but lost in federal appeals court.

The U.S. Supreme Court later refused to hear the case in 2011, allowing the law to stand.

Nevada lawmakers didn't leave a legislative history, making it difficult "to speculate about what motivated legislators nearly a century ago," Balboni wrote.

"It is reasonable to presume that their intent related in some way to preserving the health, safety, welfare and morals of the state's citizens," she wrote.

Meanwhile, as every Las Vegas tourist knows, escort services and their promoters pass out advertisements to passersby on the Strip today.