Three government agencies responsible for ensuring food and drug safety and curbing disease have recalled furloughed workers to investigate outbreaks.
The Atlanta-based U.S. Centers for Disease Control and Prevention brought back 10 of roughly 9,000 furloughed employees Tuesday to monitor food-borne disease outbreaks, including a cluster of salmonella cases tied to tainted chicken. It's unclear whether they're being paid.
The same outbreak prompted the U.S. Department of Agriculture to recall one furloughed public affairs worker to put out a health alert Monday.
"This is one of those outbreaks they're worried about," ABC News chief health and medical editor Dr. Richard Besser said. "The number of people hospitalized by this salmonella is higher than they would expect, and the strains of the organism, many of them are resistant to antibiotics."
The U.S. Food and Drug Administration, meanwhile, has "called a couple of technical experts back in to help" investigate an outbreak of nonviral hepatitis in Hawaii linked to the dietary supplement OxyElite Pro, an agency spokesman told ABC News.
"This is very frightening," Besser said of the outbreak of liver disease that has sickened 29 people and killed one. "The company stands by their product, but they said they're recalling it for now. They're not putting any more on the market. If you have OxyElite Pro, don't use it at all."
Besser said he thinks the government shutdown, which is in its ninth day, has affected public health "in a big way."
"I think we are all at great risk here," said Besser, who served as acting director of the CDC during the 2009 swine flu outbreak. "The CDC can call people back to assist when they think there's a national emergency. But their job is to be looking for these in the first place, and they're not able to do that.
"We are all at risk until they get back up to staff."
ABC News' Gitika Kaul contributed to this story.