During treatment for breast cancer in 2002, Evelyn McKnight had learnt that she would have to fight a second serious disease: Hepatitis C , CBS News medical correspondent Dr. Emily Senay reports.

"We were completely confounded," McKnight said. "We had no idea where I could have gotten that."

Soon her husband Tom, a family physician in Fremont, discovered some of his patients had also been infected.

"The only common denominator was that we were all cancer patients," McKnight said.

And they all were receiving chemotherapy at the same cancer-treatment center.

In the end, 99 people were infected, the largest outbreak of its kind in North American history. The cause: Nurses were discarding used needles, but were reusing the syringes, thereby passing the infection from patient to patient.

"It's a constant worry about am I going to wake up and be jaundiced?" McKnight said. "Is this the day that cirrhosis is going to show up?"

Since 1999, The Centers for Disease Control has tracked 31 outbreaks including Norman Okla., at a pain treatment clinic. In 2002, 71 were infected there. Other outbreaks include:
• Los Angeles, from blood-sugar testing at retirement center (2003-2004).
• Baltimore, Md., at a cardiology center (2004).
• New York City, anesthesia for a colonoscopy (2007).
These known outbreaks could be just the tip of the iceberg.

"There's no excuse for this. It's on the order of driving against traffic on the freeway; it's that reckless," said the Center for Disease Control's Dr. Michael Bell.

He blames these outbreaks on sloppy infection-control practices in out-patient settings, which are not regulated as strictly as hospitals.

"The problem with non-hospital settings, ambulatory settings, is that a lot of times there's less of a framework to make sure people do things right every time," Bell said.

Anesthesiologist Rebecca Twersky of Long Island College Hospital demonstrated one way infection can easily be spread with multi-dose vials designed for use on more than one patient.

"What you shouldn't do is take the same syringe that I just used before go back into that bottle and take out the medication," Twersky said. "Even if you've changed the needle, if you're still using the same syringe."

Then you've contaminated the bottle.

"Then in comes the next patient, and you know you go through the whole process not realizing that patient A might have put their microscopic blood particles into the multi-dose vial," Twersky said.

Evelyn McKnight founded a patient advocacy group and she is now lobbying Capitol Hill to mandate better infection control in outpatient settings.

"You should not feel like looking for healthy care is a high-risk behavior," McKnight said. "Every patient is longing to feel safe when they seek health care."