Marissa Harshman of the Vancouver Columbian reports the number of probable salmonella cases linked to Vancouver’s On the Border restaurant is increasing, but health officials are still unsure of the source of the bacteria.

Clark County Public Health on Tuesday shut down the Mexican restaurant at 1505 S.E. 164th Ave. in response to a Salmonella outbreak. To date, health officials have confirmed 11 cases of salmonella and suspect another 10 people also have the bacterial infection. Lab tests to confirm those probable cases are pending, said Don Strick, Clark County Public Health spokesman.

Dr. Alan Melnick, Clark County health officer, said Tuesday the only thing the ill people have in common is they ate at On the Border between Sept. 20 and Oct. 8. All are adults; two have been hospitalized for dehydration, he said.

Health officials are still investigating the source of the illness. They’re unsure whether the bacteria was spread by a contaminated surface or food product, or whether a food handler passed the illness to customers.