A study examining thousands of cases of ultrasound-guided procedures, such as biopsies, found infections only occurred in about one out of 1,000 procedures.

The study, published Tuesday in the American Journal of Roentgenology, is one of the first examining the risks of a variety of common ultrasound-guided procedures, the researchers said.

For the study, doctors at the Mayo Clinic looked at more than 13,534 procedures performed between January 2006 and December 2007. These included biopsies, fine-needle aspirations, drain placement and pseudoaneurysm thrombin injections. The researchers found infections by combing through patient's electronic records and through the radiology department's follow-ups up to one year after treatment.

Despite looking at thousands of cases, the researchers found only 14 infections, with 11 likely and three probably associated with ultrasound-guided procedures, for an infection rate of 0.1 percent. Of the infections, there was only one known fatality, of a patient who died five days after a parecentesis, from multiple organ failure.

"We found that the incidence of a serious infection after ultrasound-guided intervention is low," wrote the researchers, led by Dr. John M. Knudsen, an assistant professor of radiology with Mayo Clinic in Rochester, Minn. "Nearly all patients with an infectious complication improved on antibiotics alone."

Breaking down the data, the researchers found the highest incidence occurred after ultrasound-guided core organ biopsies - 10 infections out of 5,487 procedures. Of these, liver transplant biopsy had the highest incidence, close to one percent. However, the researchers said these results could be distorted by the small number of cases.

The researchers also cautioned that the study had some limitations: because they coded infections by looking at microbiology records and examining hospital admission data, some infections, especially minor ones like cellulitis, might have been missed.

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