In 2007, an outbreak of multidrug-resistant Salmonella Newberg infection that sickened at least 42 people was linked to ground beef sold by Safeway in four western states. The source of the contaminated meat was never found.

Now, a new study in the August edition of the Journal of Food Protection shows that tracing back the ground beef to its origin might have been possible had the supermarket taken two key steps: 1. Kept meat from different suppliers separate, and 2. Maintained more detailed grinding records.

Researchers found that because the supermarket chain (not named in the study) ground and then mixed meat from multiple sources, “it is likely that individual ground beef products were routinely commingled with the next batch of ground beef, although incomplete grinding logs at some store locations hindered conclusive findings on this point.” 

The drug-resistant bacteria most likely would not have contaminated so many batches of beef  — and might not have resulted in so many illnesses — had it been isolated to its original source, the authors say.

Food producers who grind meat on-site should know exactly where all the batches came from, as well as record when they were ground, so that customers’ purchases can be traced back more efficiently during investigations of foodborne illness, the study suggests.

On a positive note, the authors said that in the 2007 outbreak, access to customer’s “loyalty,” or “club” card histories was instrumental in helping investigators determine where the ground beef had been purchased. But they hit a dead end trying to figure out who supplied the retailer with bad meat.

“Detailed grinding logs are essential for the successful traceback of contaminated beef when implicated in outbreaks and to allow focused, detailed, and prompt recalls to prevent additional infections,” says the report.

The review also pointed out that Safeway’s grinding outlets did not clean their meat grinders between batches, another factor that likely contributed to the comingling of contaminated beef with clean beef, and made it impossible to identify the source of the tainted meat.

Supermarkets should change their protocol to include these precautionary measures, the authors recommend.

Taking steps to avoid cross-contamination becomes even more important when it comes to drug-resistant bacteria, because these so-called “super-bugs” can cause particularly virulent infections in humans.  While antibiotics themselves are not generally used to treat Salmonella patients, except the most severe cases, antibiotic-resistant Salmonella tend to be much more dangerous, causing a higher rate of hospitalizations and deaths.  

Of the more than 1 million confirmed cases of Salmonella each year, about 20,000, or .00002 percent of those, result in hospitalization, according to a 2011 report from the Centers for Disease Control and Prevention.  

However, during the 2007 outbreak of Salmonella Newport, almost half (46 percent) of the 42 outbreak victims were admitted to hospital, according to the study.

For this reason, the authors recommend that “state and national level surveillance systems for MDR [Multidrug-Resistant] Salmonella Newport need to be maintained to enhance detection of outbreaks.”

And in order to prevent the growth of drug-resistant bacteria in the first place, the report also suggests that antibiotics be used in food-animal production only when necessary.


“The judicious use of antibotics in animal agriculture is important to decrease the emergence of resistant pathogens,” say the authors.