Beijing ? They walked from the hospital into the morning sunlight after four months, their gaits tentative but their faces betraying delight — a college student and a middle-aged woman, China’s last two SARS patients, finally going home.

Not a surgical mask was in sight Saturday as government officials and battalions of nurses in crisp white uniforms sent Sun Zheng and Lu Zhiyan on their way. But the celebrations and self-congratulations Saturday were tempered by a message: The struggle to figure out the mysterious disease goes on.

“Our message is this: Stay vigilant,” said Han Demin, deputy director of the Beijing Health Bureau. “Is it lurking around, waiting to come back? At this point, we just don’t know.”

More than 800 people around the world died of severe acute respiratory syndrome before it subsided in June, most in Asia. In mainland China, 5,327 people were sickened and 349 died from the disease. More than half of those were in Beijing, the hardest-hit city in the world.

At Ditan Hospital, which became one big SARS ward, the staff treated more than 300 of those patients since March — including some of their own colleagues who fell ill while treating other SARS victims. Many worked long days under quarantine and could not see loved ones for weeks.

“It hasn’t been an easy five months,” said Zhao Chunmei, a nurse. “For so long, we didn’t know what was happening.”

Saturday morning, though, was a time for optimism. A red banner at the hospital gate said, “No more SARS — let’s turn our attention to tomorrow.”

Sun, 19, and Liu, 45, carrying elaborate bouquets, greeted the assembled crowd with good humor and a bit of bewilderment. Sun, summoned to the stage to speak, called his nurse, Liu Shaodong, to join him and gave her a bear hug.

The spread of SARS during April and May turned Beijing into a ghost town, with many fleeing to the countryside and stores and restaurants shutting their doors as those who walked the streets did so with their faces shrouded by surgical masks. But the city bounced back and today appears outwardly normal.

China's last two SARS patients, Sun Zheng, center, and Lu Zhiyan, left, celebrate after receiving presents during a ceremony in Beijing. The two finally went home Saturday. SARS has killed 349 people in mainland China.

“This fight has brought our society to a new level and made us more able,” said Niu Youcheng, a Beijing health official.

The Chinese government declared SARS under control last month and the World Health Organization lifted a travel warning to Beijing that had been in place since springtime.

But medical investigators, who believe the virus jumped from animals to humans, say it could remain rampant among wildlife. Researchers have warned the disease could re-emerge when cold weather returns.