Health officials should undertake spot checks to make sure schools are clean and infection-free.
That is the verdict of Hugh Pennington in his damning report, published last week, into the 2005 E. coli outbreak that made 157 people ill and led to the death of five-year-old Mason Jones.
In his report, Professor Pennington, a microbiologist, called on local authorities to inspect schools regularly for unsanitary toilets and poor handwashing facilities.
Mason, a pupil at Deri Primary, near Bargoed, died from a deadly strain of E. coli after eating meat supplied by the Bridgend butcher John Tudor Sons.
William Tudor was later jailed for 12 months after he admitted supplying the contaminated meat that made children ill at 44 schools in Bridgend, Caerphilly, Merthyr Tydfil and Rhondda Cynon Taf.
Last week's report blamed Mr Tudor entirely for the outbreak.
But the inquiry also uncovered serious flaws in the handling of school meal contracts and a failure of the Assembly government to deal with school hygiene concerns.
The inquiry heard that complaints from school meal supervisors and health inspectors about the quality and hygiene of the meat - some of which was found with insects on it - had been ignored.
Professor Pennington's report also criticised the government's failure to follow the recommendations of Peter Clarke, the former children's commissioner for Wales, in a 2004 report that lamented the poor state of school toilets.
Professor Pennington wrote: "The provision of adequate facilities in schools is a basic requirement and it takes on a particular importance in terms of preventing the spread of infection."
He accepted that money had been spent to improve toilets and other facilities in the four authorities affected. But this had been after the outbreak, not before.
In Merthyr Tydfil, schools now have hygiene checklists for toilets and qualified officers undertake regular inspections. It has also appointed procurement experts to handle contracts for school meals.
Professor Pennington previously held an inquiry into an E. coli outbreak in Scotland. He was disappointed that Wales had not learnt lessons from this, and he called for a review of food hygiene laws within the next five years.
First Minister Rhodri Morgan said the government would carefully consider Professor Pennington's proposals. "Our aspiration is that the chances of a repeat of this kind of outbreak will be minimised, even if the risk can never be wholly eliminated," he said.
The Welsh Local Government Association said lessons would be learnt from the outbreak.