San Francisco public health authorities confirmed Friday that a café worker must have spread typhoid fever between April 16, 17, 18, 20 or 27 when he was diagnosed with a bacterial infection.

The Guardian Express reports that anyone who ate at Nordstrom Café at Stonestown Galleria Mall in San Francisco between those periods will be at risk of becoming ill. However, it is still unknown how many people have been infected.

Typhoid bacterial infection can be caused by Salmonella Enterica serotype Typhi bacterium, which is very rare in the United States. The Centers for Disease Control and Prevention said that typhoid fever was life-threatening with about 5,700 cases annually. Symptoms of the illness according to the SF State’s Student Health Center include weakness, fever, headache, nausea, vomiting, stomach pains, and diarrhea. And in other cases, it could cause flat rose-colored skin spots.

The worker must have contracted it when he was traveling outside the U.S. Individuals with typhoid fever carry the bacteria in their intestinal tracks and blood streams. However, a small number of individuals called carriers may recover yet continue to carry the infection.

It is still unclear how many people dined at Nordstrom Café around those dates, but employees were already informed about the case on Friday. Kara Darrow, Nordstrom’s spokesman said they are looking through their customer’s credit card records, so they can offer free typhoid testing to those who might have been exposed.