The Health Department enforces the St Louis City Food Ordinance #68597 - http://www.slpl.lib.mo.us/cco/ords/data/ord8597.htm.
By and large, this ordinance reflects the 2009 FDA Food Code, a national standard published by the Food & Drug Administration - http://www.fda.gov/Food/FoodSafety/RetailFoodProtection/FoodCode/FoodCod...

Specific types of violations are scored by the risk they pose to the public. A point system is used, whereby points are deducted for each violation. A score of 100 is given when there are no violations. Scores are summarized into a general grade for each inspection.

Grade A is for scores 85-100
Grade B is for scores 71-85
Grade C is for scores under 71
Some violations are considered “critical”, and must be immediately remedied. When 2 of these occur during an inspection, the Grade is dropped to “B” or “C”.

Operations that are given a “B” grade must improve within a relatively short time to avoid further sanctions. Often, downgraded establishments decide to suspend operations until they can regain their “A” rating. Operations with a “C” grade must improve immediately to avoid permanent closure. With “C” ratings, the Health department may insist that operations be suspended until problems are resolved.

There are plenty of examples of restaurant inspection violations, scores, and grades on our website.