Hélène Campbell, the Ottawa double-lung transplant recipient and viral-video sensation, has been readmitted to Toronto General Hospital after experiencing shortness of breath.

The apparent setback for the 21-year-old organ donation crusader began Saturday when she experienced a shortness of breath.

She returned to hospital Sunday night when she was taken to the emergency room due to reduced oxygen saturation, according to a blog posting late Wednesday by Campbell's mother, Manon.

"Most of the shortness of breath was felt when walking and some while at rest. So, as advised and taught before her discharge, she went to the emergency department," Manon Campbell wrote on the website A Lung Story, which has been providing updates on Hélène's treatment and recovery.

The blog entry noted that the possibility of infection and rejection of the new organs remain major risk factors, as is common for many transplant patients recovering from surgery.

Even so, her family said Campbell has kept up the bubbly personality that made her an internet phenomenon, attracting followers on Twitter such as pop star Justin Bieber and U.S. talk-show host Ellen Degeneres and engaging thousands to her cause.

'Strong and positive' attitude

Ontario's Trillium Gift of Life Network recently credited the patient's efforts to a noticeable spike in new registrations for organ donors, up to 3,000 a week from 350.

"While waiting for more tests and results, Hélène’s attitude remains strong and positive," her mother wrote. "We have run into some of the other families from the lung transplant waiting list and Hélène thoroughly enjoys catching up with them."

The blog entry added that Campbell's medical team expects that she should be returning to her family's Toronto apartment "sooner rather than later" to catch up on DVD episodes of I Love Lucy.

Before she was admitted to hospital on Sunday, Campbell managed to surprise her family members over the weekend by singing happy birthday to a relative, going on a short walk, and even showing up with a birthday cake with lit candles — something she could not have done months earlier. She had been advised to stay away from lit candles because of her oxygen requirements.

"We are very thankful for the fact that we had most of the weekend together — we also know that there will be many more to come," Manon wrote.