An investigation has been launched after 23 cases of e.coli food poisoning were identified in the south Wales valleys, mostly among children.
It is believed the cases in 12 schools in the Rhondda Cynon Taf and Merthyr Tydfil council areas are linked.
Initially there were seven reported cases, but that has now increased. The source of the outbreak is being hunted.
A helpline has been set up with five lines, on 029 2040 2520, open from 0900 to 2100 BST until Friday.
The National Public Health Service for Wales is interviewing those affected to find out the source.
The service said the e.coli 0157 cases had been identified in the past few days. A new case was confirmed on Monday afternoon.