The total number of people sickened by an E. coli outbreak linked to romaine lettuce grown on California’s Central Coast has risen to 52.

On Dec. 6, the United States Centers for Disease Control and Prevention added nine people to the original total of 43. People from 15 states have fallen ill, many seriously, though no deaths had been reported as of Dec. 6. Nineteen people have been hospitalized.

The CDC expects to learn of additional illnesses.

Government investigators have yet to trace the outbreak to a common grower, supplier, distributor or brand. CDC continues to advise consumers not to eat and retailers and restaurants not to serve or sell any romaine lettuce from the Central Coast regions of northern and central California.

Some romaine lettuce products are now labeled with a harvest location by region and are being sold at retail.