A recent salmonella outbreak has infected over a hundred people in half of the United States, and health officials have not determined what is causing it.

On Friday, the Centers for Disease Control issued anotice it was investigating an outbreak of the strain Salmonella Oranienburg. On Sept. 2, the CDC identified 20 infections, but the outbreak has grown rapidly since then.

According to CDC data, reported cases have stretched across the U.S. mainland, with Texas, 45, and Minnesota, 13, having the most reported cases. The infected people have ranged from less than a year old to 82-years-old, and 59% of sick people are females.