Denmark is investigating an increase in the number of registered cases of a type of E. coli reported in the past month.

Enteroinvasive E. coli (EIEC) is usually associated with travel diarrhea but the patients in the current outbreak have not been abroad, which suggests a common food may have made people sick, according to the Statens Serum Institut (SSI).

Between Nov. 23 and Dec. 16, 63 infected people with EIEC or ipaH-positive were registered at the Statens Serum Institut and 18 of them have been hospitalized.

EIEC was isolated from 22 patients and the remaining 41 are PCR positive for the invasion plasmid antigen H (ipaH) gene, which is specific to Shigella species and EIEC.

Patients live all over the country, and there are 43 women and 20 men sick. They are aged from 1 to 91 years old with a median age of 53.

Hovedstaden has the most cases with 23, Sjælland has 19, Midtjylland has 14 and seven live in Syddanmark.

The Statens Serum Institut, Danish Veterinary and Food Administration (Fødevarestyrelsen) and DTU Food Institute are trying to find the source of infection.

About EIEC

EIEC can cause intestinal infections and is typically seen among travelers. It is closely related to Shigella. EIEC is transmitted from person to person or through drinking and bathing water as well as foods contaminated with human or animal feces. Microscopic amounts of feces can cause illnesses.

The time between being infected and symptoms occurring is typically one to three days. Infection can cause diarrhea, stomach pain, nausea, vomiting or a fever lasting several days and usually goes away on its own. Plenty of fluids are important to prevent and treat dehydration related to diarrhea and vomiting. In case of severe diarrheal disease, consult a doctor.

EIEC primarily infects children in the developing world. There is no formal surveillance system for diarrheagenic E. coli and most laboratories are unable to identify them, according to the Centers for Disease Control and Prevention (CDC).

In 2018, the first confirmed U.S. outbreak of EIEC was found since 1971. More than 50 people were sick after a potluck party in North Carolina, but the source was not clear. Contaminated vegetables were implicated in outbreaks in Italy in 2012 and the United Kingdom in 2014. Leafy greens were linked to an outbreak in Sweden in 2017 with 83 sick.