The Health Protection Agency (HPA) is working with Birmingham City Council to investigate an outbreak of e.coli at Sutton Park in Sutton Coldfield.
Of the seven patients identified as being infected with E. coli O157 in recent weeks, five were children under eight and at least one is known to have been hospitalised.
The HPA said the strain of the bacteria was often associated with contact with rural environments that may have been contaminated by animal faeces.
– Dr Roger Gajraj, HPA's West Midlands East Health Protection Unit
The council is increasing hand-washing facilities at the park and the city council and HPA are issuing leaflets and displaying posters to warn visitors of the risks and advise on preventative measures.
The best protection against E. coli is to always wash your hands, especially after contact with animals, after going to the toilet and immediately before eating. I would also advise cyclists and walkers to wash their tyres, footwear and their hands after visiting Sutton Park as an extra precaution.