By DEBORAH STARR SEIBEL

May 18, 2008 — Season five of “Project Runway” – coming in July – will be its last on the New York catwalks before the show gets an overhaul by changing networks (Bravo to Lifetime) and locale (New York to Los Angeles). And what will make this last season even more bittersweet is that the one contestant everyone hoped would return – Jack Mackenroth – won’t be on board.

The Harlem-based designer had to exit the “Runway” early last season due to a potentially deadly staff infection. “Bravo said, ‘You certainly can audition again, but there are no promises,’” says Mackenroth, 39, who was hospitalized for five days after leaving in the middle of the fifth challenge.

“To re-audition, I couldn’t have brought the same [clothes]. I would’ve had to make new pieces, which is a huge investment in time and money. In the end, I decided I just couldn’t give up another year of my life.”Bravo hasn’t released the names of the new designers, which begins filming in June. But Mackenroth’s absence will probably be a big disappointment for passionate “Runway” fans.

His story has to be one of the most poignant in the show’s history: After showing great promise by winning the menswear design challenge, Mackenroth entered the sewing room with Tim Gunn and announced that he had a MRSA infection in his nose and would have to quit.

“It was just so scary,” says another season four contestant, Mackenroth’s friend Kit Pistol, recalling his sudden illness. Mackenroth was recently in Los Angeles visiting Pistol, who is the stylist for “Dancing With The Stars” co-host Samantha Harris.

“You’re in this crazy world where you don’t have your cell phone to call home,” says Pistol. “You don’t have your family or close friends and you’re not feeling well. And there’s all this pressure. I know Jack had auditioned [for] season three and then to be accepted [for] season four and not make it through due to health reasons was just crushing.”

But Mackenroth, who is HIV positive, knew he couldn’t take chances. He says, “I’d had this once before, in my leg, and it’s really resistant to antibiotics,” adding that a staff infection is something anyone can get and has no relation to HIV.

“The larger issue,” says Mackenroth, “is that it’s a really contagious bacteria. The producers were trying to make it work. They were going to have a special sewing machine that only I would use. But I was like, ‘Am I going to be selfish and just hope that no one else will get this?’”

So he decided to put his scissors down. “I remember we were standing by the elevators, just before we went in, and Tim was trying to comfort me because I was crying,” says Mackenroth. “And he said, ‘Listen, you’re very talented. Everything happens for a reason.’ And at the time I thought, ‘That’s a load of crap.’ Because at that moment, it didn’t feel that way. But things do happen for a reason. There was an outpouring of support. And a lot of opportunities have come my way.”

Mackenroth has a cameo in the new “Sex & The City” movie. He’s designing a red carpet dress for Heather Tom, a cast member of the soap “The Bold and the Beautiful.” And he’s up for a job with a booming, Tokyo-based, Gap-like company called Uniqlo. “The show was amazing for me,” he says. “For one thing, people answer my phone calls.”