Instead we're told to...
1. Call the suspect(s)
But as you can see from the Chronicle story, restauranteurs aren't likely to believe you and you're accusing them of hurting your health which is guaranteed to put all but the most cool headed operator on the defensive.
2. Call the Dept of Health
Sounds like 4 or more people need to be affected for any investigation to occur. Seems unlikely that 4 people would take the time to call in unless a restaurant was making a large number of people sick.
Set up a website that allows consumers to quickly report cases of poisoning and possible culprits. Make this page easy to find and prominent on the Health Department's site (I couldn't find anything about reporting food poisoning on the front page or via a quick search). If you lower the barriers to report, you'll get more information, and more information means you'll have a shot at identifying problems.
Just a thought...