Researchers tend to suspect a “common-source outbreak” when a cluster of cases show seven or fewer allelic differences in the letters of their genetic code. There are 2.5 to three million ...

For the other two outbreaks, posted on March 13 and April 9, the patient counts stand at 30 and 15, respectively. The FDA has not yet determined a source for the pathogen in any of the outbreaks ...

After conducting an investigation, the FDA concluded that contaminated romaine lettuce was the source of the outbreak. The agency also acknowledged a common grower of the lettuce but redacted the ...