Enlarge / A Wendy's old-fashion burger. Romaine lettuce on Wendy's burgers is thought to be the cause of the outbreak. (credit: Getty | Francis Dean)

We will never know for certain what caused a large, multistate outbreak of E. coli O157:H7 infections linked to Wendy's restaurants late last year, according to a new study led by investigators at the Centers for Disease Control and Prevention.

The study, highlighting weaknesses in our ability to respond to foodborne outbreaks, lands amid a separate report published by the CDC finding that, in general, we're also failing to prevent outbreaks. In fact, cases from some common foodborne pathogens have increased relative to pre-pandemic levels.

In the outbreak last year, which spanned from July to August, at least 109 people in six states fell ill, with 52 needing to be hospitalized. Eating at Wendy's was a clear link. But it wasn't enough to crack the case.

Enlarge / Chicken eggs are disposed of at a quarantined farm in Israel's northern Moshav (village) of Margaliot on January 3, 2022. (credit: Getty | JALAA MAREY / AFP))

The ongoing bird flu outbreak in the US is now the longest and deadliest on record. More than 57 million birds have been killed by the virus or culled since a year ago, and the deadly disruption has helped propel skyrocketing egg prices and a spike in egg smuggling.

Since highly pathogenic avian influenza (HPAI) A(H5N1) was first detected in US birds in January 2022, the price of a carton of a dozen eggs has shot up from an average of about $1.79 in December 2021 to $4.25 in December 2022, a 137 percent increase, according to data from the US Bureau of Labor Statistics. Although inflation and supply chain issues partly explain the rise, eggs saw the largest percentage increase of any specific food, according to the consumer price index.

And the steep pricing is leading some at the US-Mexico border to try to smuggle in illegal cartons, which is prohibited. A US Customs and Border Protection spokesperson told NPR this week that people in El Paso, Texas, are buying eggs in Juárez, Mexico, because they are "significantly less expensive." Meanwhile, a customs official in San Diego tweeted a reminder amid a rise in egg interceptions that failure to declare such agriculture items at a port of entry can result in penalties up to $10,000.