The E. coli O55 mystery continues in Dorset, UK.

It first emerged in July 2014, when two children were hospitalized with acute kidney problems and has since caused outbreaks of infectious diarrhea.

To date the O55 strain has affected 30 people, 10 of them children in areas including Bournemouth, Poole, Weymouth, Blandford and Christchurch. It also affected two cats.

All 10 children and one adult were hospitalized after they developed the complication of hemolytic-uremic syndrome (HUS) which affects the kidneys.

Noeleen McFarland, from Public Health England, told BBC’s Inside Out South: “When it was confirmed we knew we had uncovered something unusual that hadn’t been seen in the UK before.”

Despite an investigation, tests and screening, the source of the strain, which produces a toxin that can lead to fatal kidney failure, has never been traced.

Public Health England said any previous cases of the O55 strain in the UK had been associated with travel.

Following the outbreak, officers were sent out to investigate and test play parks, swimming pools and restaurants visited by those infected seven days prior to them being ill.

“Everything we investigated, tested and sampled was all negative,” Mrs McFarland said.

Isaac Mortlock, aged four, from Bournemouth, was hospitalized after contracting the strain.

Isaac’s mum Gabrielle Archer said: “His kidney function didn’t return to normal and we’ve been told he will need a transplant in the future.”

A new test is being developed to detect the O55 strain and it is hoped the test will be ready for use on animals in the new year.

The new test is being worked on by scientists at the Animal and Plant Health Agency (APHA), based in Surrey using microscopic magnetic beads which picks out the E. coli O55.