Juice drinkers might want to take note: Unprocessed juices can be dangerous to children, the elderly and anyone with a weakened immune system.

So dangerous, in fact, that earlier this month the Food and Drug Administration started requiring a warning on fresh apple juice and apple cider that hasn't been processed.All other unprocessed fruit and vegetable juices will begin carrying the same warning by Nov. 5. (Initially, companies can meet the requirement by placing the warning statement on signs that are displayed next to the products.)

According to FDA spokeswoman Judith Foulke, only about 2 percent of all juices sold in the United States have not been processed to kill harmful microbes. Most of those are sold at cider mills and farm markets, although some are carried in grocery stores.

But the danger, while small, is very real, she said. Between 16,000 and 48,000 cases of foodborne illness have been traced back to unprocessed juices each year. Among the most serious illnesses linked to the juices are E. coli, which causes severe illness and even death.

Symptoms of E. coli are diarrhea, nausea, cramping and fever.

Until now only orange juice has been required to say whether it has been pasteurized.

The FDA is considering a requirement that all manufacturers of packed fruit and vegetable juice change their production process to prevent microbiological, chemical and physical contamination of their products. The desired result would be a 100,000-fold reduction in the number of harmful microbes found in juices. If that requirement is implemented, it will also eliminate the need for the warning statements on juice.