Hamburgers are a classic American food, but a new report released Tuesday said over one in 10 burger products sold in the United States are "problematic," including a few with rat DNA.

Clear Labs, a private US food testing company, performed a genomic analysis of 258 anonymized samples of ground meat, frozen patties, fast-food burger products, and veggie-burger products from 79 brands and 22 retailers in the United States.

The results, which were not peer-reviewed, showed that 13.6 percent of the products had problems with unexpected or missing ingredients, hygienic issues or pathogenic contamination.

Vegetarian products especially did not fare well. Of the 89 vegetarian products they sampled, 23.6 percent showed some form of discrepancy between product and label.

That included two detections of meat in vegetarian products and one detection of no black beans in one black bean burger.

One of the biggest concerns is that 4.3 percent of the samples, or 11 of the 258 products, contained DNA of pathogens such as Yersinia pseudotuberculosis, which can cause tuberculosis-like symptoms, and Aeromonas hydrophila, which can cause gastroenteritis.

Michael Doyle, professor of food microbiology of the University of Georgia, however, said that the weakness of the genomic analysis is that it cannot differentiate between live and dead cells and that finding the DNA of Salmonella or E.coli from a dead cell is not very helpful.

In addition, the pathogens found in the new research are not of common concern in foods or unable to cause illness unless they are present at high enough levels, said Doyle.

"I think their results may be a bit misleading in that sense," he said.

The analysis also detected human DNA in one sample of frozen vegetarian burger and rat DNA in three samples, including one fast food burger, one vegetarian burger, and one ground meat sample.

"While unpleasant, it's important to note that it is unlikely that human DNA or rat DNA is harmful to consumer health," the report said.

"What many consumers don't know is that some amounts of human and rat DNA may fall within an acceptable regulatory range. The amounts we detected in our research most likely fell within the acceptable regulatory range as we understand them."

Doyle expressed similar views. "It's not surprising to find some rat or human DNA in foods," he said. "It sounds gross, but you have to put that in perspective. It's more of an aesthetic concern than one relevant to human health."