Tracking and tackling foodborne germs.

Food poisoning sickens millions of people-and kills thousands-in the United States each year. Estimated costs of treatment and lost productivity associated with these cases run to $22 billion a year, according to a report released last week by the General Accounting Office, a congressional agency. Researchers report, however, that they are homing in on the germs that cause food poisoning and are experimenting with novel strategies to keep them from spreading. The scientists spoke in New Orleans this week at a meeting of the American Society for Microbiology.

One research team revealed that kitchen sponges and dishrags may develop into rich reservoirs of germs. Carlos Enriquez and his coworkers at the University of Arizona in Tucson cultured microbes from 325 cellulose sponges and 75 cotton dishrags taken from households. Most harbored large numbers of virulent bacteria that commonly infect animals and people, as well as pathogens that cause illness only in infants or persons with unusually weak immune systems.

Moreover, Staphylococcus aureus turned up in 20 percent of the sponges and cloths. Each year, this bacterium causes 1.5 million cases of food poisoning and about 1,200 deaths in the United States. Another 14 percent of the sponges and cloths hosted Salmonella, bacteria that the GAO report linked to as many as 3,800 U.S. deaths in 1993.

Enriquez concludes that unless sponges and other cleanup materials are disinfected regularly, they may spread the germs they were meant to remove. In hopes of reducing human exposure to eggs contaminated with Salmonella enteritidis, immunologist Peter S. Holt of the Agriculture Department's poultry research lab in Athens, Ga., has turned his attention to the spread of infection in the hen house. He recently showed that a common method of rejuvenating aging hens takes a toll on the birds' immune system.

After producing an egg a day for 30 or 40 weeks, a hen's output can wane dramatically. Farmers often put such a bird on starvation rations. Her weight can drop 30 percent in just 2 weeks, she molts, and her egg laying grinds to a halt. When returned to full feed after several weeks, Holt explains, "these molted birds can produce about 90 percent of what their optimum was before." While unmolted hens usually have to ingest about 50,000 Salmonella cells to become infected, molted birds need fewer than 10, Holt found.

Once infected, these hens shed far more germs in their feces than unmolted birds and are more likely to lay contaminated eggs. Moreover, Holt reports this week, Salmonella spread through the air among the molted birds, despite the conventional wisdom that this germ infects animals solely through ingestion of contaminated feces.

This finding argues, he says, that farmers should find less stressful ways to increase egg production and become especially vigilant about preventing infections in molted hens. At Texas A&M University in College Station, Steven C. Ricke and his colleagues have taken another tack. They found that a new antibacterial bath significantly reduces the number of Salmonella associated with eggs.

Brandt Rice of the Naval Medical Research Institute in Bethesda, Md., reported preliminary success with another approach to limiting foodborne pathogens: treating young broiler chickens with a human vaccine against Campylobacter, a bacterium that can cause severe diarrheal disease in people. Before cooking, 40 to 80 percent of retail poultry products in the United States harbor the pathogen, Rice says.

His data indicate that vaccinated birds exposed to Campylobacter do not host as many bacteria as exposed birds that have not been vaccinated-sometimes only 17 percent as many. Finally, Gordon E. Schutze of Arkansas Children's Hospital in Little Rock points to the need for household sanitation that extends well beyond the kitchen. He reports tracing salmonellosis in infants to fecal contamination from infected family members-including several with symptomfree disease. In one house, a vacuum cleaner picked up Salmonella from the dust.