What is a significant risk associated with undercooking hamburger?

Undercooking hamburger presents a significant risk because ground beef may harbor harmful bacteria such as E. coli, Salmonella, or Listeria, which are present in the meat if not cooked thoroughly. These bacteria can lead to foodborne illnesses, which can be severe and, in some cases, fatal. When ground beef is not cooked to the recommended internal temperature of 160°F (71°C), it is possible that these pathogens survive, posing a serious health risk to consumers. Proper cooking kills these harmful microorganisms, thus ensuring food safety and reducing the risk of illness.

Regarding the other options, while undercooked hamburger may be chewy or result in spoilage if not handled properly, these concerns are not as critical in terms of food safety as the risk of bacterial survival. Elevated sodium levels primarily relate to the seasoning or added ingredients in the hamburger rather than the cooking process itself, making it less relevant in the context of undercooking.