As infection rates have risen in recent years, policymakers have increasingly sought to improve the accuracy of the CDC’s “Influenza-like Illness Index” (LIII), which uses population size, climate, and other data to estimate flu activity nationwide. Yet the LIII, which includes data since 2008, is widely reported as derived from 2012 data. The CDC reportedly identifies active and mild flu outbreaks in every U.S. county regardless of LIII publication date. (The CDC offers no official dates for LIII publication.) The error may be negligible. But when local officials want to measure population responses to disease outbreaks, it can be crucial.

Now an outbreak of E. coli blamed on imports of raw tomatoes, colloquially known as the E. coli 0157:H7 virus, which has been identified in 18 states, is being reported as spreading to North Korea, according to STAT’s Daniella Diaz. North Korea has been subject to a travel ban since 1991. Its two nuclear tests, in 2006 and 2013, outraged the world and angered neighboring countries, which responded with higher sanctions and isolation.

Although the virus has been linked to red pepper, Russ Lammers, a senior epidemiologist at Minnesota’s Carver County Health Department, says it may be significantly larger: “The disease has the potential to be on par with the Blue IV outbreak,” which began in August 2001. It was the deadliest United States outbreak of E. coli at that time, with 230 people infected and 23 hospitalized; the three people who died were 14-year-old boys from southwestern Minnesota.

Some officials fear that the severity of the current outbreak, which occurs every seven years or so, may explain the lingering isolation of North Korea.

The CDC estimated in 2007 that an influenza outbreak may occur once every four years and may cause between 2,500 and 6,000 hospitalizations annually. Prior to the outbreak, North Korea was recognized as being at one of the highest risk of an influenza pandemic; one of the CDC’s global pandemic centers is located in Minneapolis-St. Paul.

The plant at the center of the outbreak, Mexican beef, is a staple of North Korean meals. While investigators are still trying to identify the precise source of the E. coli 0157:H7 outbreak, experts speculate it could have originated in Mexico, where not all of the beef caught the disease in Mexico. Since 2003, North Korea has been burdened with a separate outbreak of E. coli 0157:H7, from imported beef, which caused 614 illnesses.

For more information, see a Q&A and a full review of the outbreak and its source.