Kate Leong of Phoenixville says that more than 4.3 million visitors have come to her blog, "Chasing Rainbows," for the same reason people stop and watch a car wreck.

"When there's a tragedy," she says, "people need to slow down and look and stay a while."

She underestimates herself and her readers.

Kate, 43, is a gifted storyteller, and her accounts of her son Gavin's life, and death, now draw 25,000 to 30,000 visitors a day. Her blog is raw, honest, and immediate.

She posted from the ICU at 2:30 a.m. April 11 after Gavin, 5, suffered a seizure and cardiac arrest. She took her younger son, Brian, 4, in to see him.

"I kept thinking - if Gavin does die, I want Brian to know that he said goodbye," she blogged. "I sat him on the side of Gavin's bed and he whispered in his ear. I don't know what he said to his big brother, except I heard 'I love you' at the end. It ripped my heart in two."

Responses poured in:

2:59 a.m.: "Can't stop thinking of you and your sweet Gavin. Sending love (it's total stranger love, but as I sit here with tears streaming down my cheeks, it feels pretty real to me)."

5:03 a.m.: "Being in Australia, I have been able to follow your journey. Keep the updates coming Kate as there is a whole world behind Gavin and you."

5:05 a.m. "I can't sleep and you are in my thoughts. Much love from the West Coast."

After Gavin died April 14, Kate asked readers to donate to the child life team at Nemours/Alfred I. duPont Hospital for Children in Wilmington or to Gift of Life Family House in Philadelphia, where families stay awaiting organ donation.

Each got over $13,000. At duPont, scores of baby dolls, rattles, books, and whistles arrive daily.

"We've never experienced this magnitude," said Alaina Norvell, with the duPont child life team.

In just days, she raised $18,000 for the Chester County Intermediate Unit, which helped disabled students like Gavin in school. Kate blogged Tuesday about cleaning out his cubby - his cup, a change of clothes, butterflies other students had made for him with construction paper.

"After I hugged everyone goodbye and walked to my car . . . carrying a bag of the things he left behind . . . the tears started to flow. And they wouldn't stop. All the way home . . . all the way inside . . . all the way to Gavin's room to the rocking chair where I once held him and fed him and sang to him."

Blogging from her kitchen, or the ICU, Kate never realized she was part of a revolution - the rapid proliferation of what are known as patient blogs.

Lisa Gualtieri, a professor at Tufts University School of Medicine, studied 250 patient blogs last year and published her findings in the Journal of Medical Internet Research.

Most blogs are read by few, and a few by many. Most bloggers fit Kate's demographic: Caucasian, age 25 to 55, highly educated, predominantly female.

Gualtieri estimated there are tens of thousands of patient blogs, and disputed Kate's contention that readers come to her blog to rubberneck. She found that readers of patient blogs are quite sincere, and come for inspiration and information.

Of Kate's blog, Gualtieri says, "It's an enormous audience, far beyond what most bloggers have. I think it's wonderful if it helps her and she feels like her telling her son's story has helped others."

Kate longed to be a mother, not a blogger.

The youngest of five from Plymouth Meeting, Kate Gallagher dropped out of nursing school months before graduation.

"I kept getting in trouble for getting too involved with families," she said. "So I became a flight attendant."

She had nearly given up on motherhood when, at 34, she met Ed Leong on a flight to Puerto Rico in 2004. Kate never flew to Puerto Rico because her curly hair would frizz in the humidity. But a colleague begged her to switch, and there was Ed in first class on an upgrade.

Ed, now 42, graduated from the University of Pennsylvania and worked in IT. After they married in 2006, Kate lost a set of twins, got pregnant with twins again, and lost one in pregnancy. Gavin, the other, was born Sept. 29, 2007.

"Believe me when I say - there is nothing in this world worse than a silent delivery room," Kate blogged.

Gavin couldn't breathe on his own, and spent a month in intensive care.

He had such poor muscle tone doctors told Kate he'd never sit up, never feed himself. Doctors eventually lumped his myriad problems into a diagnosis of cerebral palsy, but Kate never accepted it.

In the first days, Kate set up a CaringBridge.org page, as families facing hospitalizations often do, to keep loved ones informed. It was easier than calling everybody. More than 430,000 CaringBridge sites have been created since the website's founding in 1997.

Kate grew to love posting daily updates.

"My writing has always been my therapy," she said. "I know very well what can happen if I keep things inside. I kind of self-destruct."

After a few months, she outgrew CaringBridge and created "Chasing Rainbows" at www.kateleong.com.

"I wasn't really looking for a bigger audience," Kate said. Her thinking early on was: "If people are touched or inspired or given hope, or learn a tip that can help them with their child, that's kind of accidental. I'm really grateful, but it's sort of like extra."

For Ed, having his life so public was jarring. But he realized: "This is so important to Kate. It's more important for her to be happy."

Ed realized that other parents were drawing encouragement from Kate's positive attitude, and readers were sharing ideas, resources, and suggestions.

He added, "I also saw the advantages for other moms, who were reading her, and also for Gavin."

Indeed, Kate's thinking had evolved, and so had her blog.

"It started on CaringBridge with me just keeping family updated," she says. "Then it was totally my therapy - especially on long days with Gavin alone. Then more people started reading and offering advice. Then more special-needs moms joined in and we swapped tips and tricks. I have always said that every visit to my blog, to me, is like another prayer or positive thought for my family and especially for Gavin.

"I do care about my readers and in a way many of them have become like an extended family. . . . I'm grateful to have this platform and over the years it has helped me find ways to help Gavin. And it helped me to help others."

One example: "I did a lot of research on stem cell therapy and wrote about a certain doctor doing clinical trials at Duke University. Gavin wasn't eligible, as it turned out," Kate said, but a reader contacted her. "I put her in touch with the doctor and her son had the stem cell transplant and did very well."

Kate's blog and others like it are emblematic of another big trend in health today - the use of the Internet by patients to change the face of health care. This is known as patient engagement.

WEGO Health, an Internet home of 50,000 health activists, "estimates that there are well over a million health bloggers, and many more people using" social media, said chief executive officer Jack Barrette.

Involvement often goes far beyond blogs.

Breast cancer patients have an extremely active Twitter group, #BCSM, with weekly tweetchats on Mondays. Thousands of the world's sickest patients share information on cures and treatments on www.patientslikeme.com.

The Internet and social media technology have unleashed the power of patients to change health care from the bottom up, said Barrette, whose site is www.WEGOhealth.com.

Six months after Gavin was born, Kate was pregnant again with Brian, now a beautiful 4-year-old. Brian became Gavin's greatest friend and teacher: Gavin would see what his little brother would do, and try to model him.

Ed and Kate felt they should have a third child, a sibling to help Brian with Gavin later in life. Kate has suffered nine miscarriages and a stillborn daughter, Darcy Claire.

She blogged through it all.

Parents Magazine in January nominated "Chasing Rainbows" for an award as the blog "most likely to have you reaching for your tissues." It didn't win, but coverage generated enormous attention.

Another popular blog, "Momastery," asked Kate to write a guest entry. There, on April 3, republished on her blog, she revealed all: "After suffering sexual abuse as an adolescent at the hands of a teacher," she wrote, "I went down a road of self destruction."

She described how she almost died in high school from an eating disorder, then tried to commit suicide, was raped as a flight attendant, and became an alcoholic for five years.

"One day," she blogged, "I was given a choice - marriage or vodka. Lucky for me, I had a choice. Lucky for my family, I chose wisely."

Just a week after that was published, Gavin suffered his seizure and cardiac arrest. And by April 14, he was brain-dead.

On April 13, knowing Gavin was dying - and that her birthday was the next day - Kate asked readers to do an act of kindness in Gavin's name. Many responded - their kindnesses directed at Kate.

One sent her a flag that had flown over the Pentagon. Another said he would run the Broad Street Run in Gavin's honor. Gavin had a favorite fire truck, No. 8, on a kiddie ride at Gillian's Wonderland Pier on the Ocean City boardwalk. Owner Jay Gillian, contacted by a reader of the blog, painted "Gavin" on the fire truck.

Kate has a Facebook page with more than 20,000 "likes," and many of the acts of kindness are listed there.

On her birthday, the day her son would be declared brain-dead, Kate woke up in the bed next to Gavin, knowing, astonishingly, that she was pregnant. She could feel it. She was sure Gavin waited to die until Kate discovered she was pregnant.

She called it "the most unbelievable twist of fate," and blogged, "Gavin has always been generous."

Kate believed that Gavin, a boy who never spoke, had used her and her blog to influence so many people, to help and inspire so many. Even in death this continued. The family donated his organs.

As he was being wheeled into surgery, Kate pasted a sign on his bed: "Superhero Gavin off to save lives."

More than 400 went to the viewing, and 400 to the funeral on April 23. Kate gave the eulogy, also posted on her blog.

"The message here is not 'go home and hug your kids' - because we all do that," she said. "The true message here is don't lose hope. And never let anyone tell you that you can't chase rainbows."

Contact Michael Vitez at mvitez@phillynews.com or 215-854-5639. On Twitter @michaelvitez.