Health officials in Pennsylvania are advising customers of Stump Acres Dairy in York County to discard any raw milk purchased from the dairy after a sample tested positive for Listeria monocytogenes, local news station WHPTV reports. The Pennsylvania Department of Agriculture collected the sample on April 24 and confirmed the presence of the Listeria bacteria Thursday. No illnesses have been reported. Symptoms of Listeria infection generally take three days to three weeks to appear. In 2007, raw milk from Stump Acres caused a Salmonella outbreak that sickened 29 individuals, which prompted the agriculture department to revoke the dairy’s raw milk license. Pennsylvania state law allows for licensed dairies to sell raw milk, though Stump Acres has reportedly been operating without a license since the 2007 outbreak. The Pennsylvania Department of Health is advising anyone who drank milk from Stump Acres and experiences symptoms of Listeria poisoning to contact a healthcare provider.