The outbreak of rare Salmonella in Iowa, first reported in late July, still has investigators stumped looking for its source. At least 31 people across 19 Iowa counties fell ill with a “relatively uncommon” strain of Salmonella Enteritidis, though more than a week has passed since the last illness was reported, according to Dr. Patricia Quinlisk, medical director at the Iowa Department of Public Health. “Our number of cases has decreased significantly,” Quinlisk said. “There were no common exposures nor any links to anything happening nationally.” In an earlier report, the health department had suspected chicken or eggs might have caused the outbreak, but that lead does not appear to be producing results. Iowa has also been hit hard in recent months by a massive outbreak of Cyclospora connected to salad served at Olive Garden and Red Lobster restaurants. That outbreak has sickened at least 548 individuals, including 153 in Iowa, according to the latest count by the U.S. Centers for Disease Control and Prevention. Salmonella is a toxic bacteria that can cause diarrhea, fever and abdominal cramping within 12 to 72 hours of infection. Cyclospora is a single-celled parasite with symptoms that include diarrhea, vomiting and nausea within several days to several weeks after infection.