If you slurped down a dozen oysters this past weekend and spent Monday curled up on the bathroom floor questioning every life choice that led you to that raw bar — you're not alone.

Reports are piling up across the city of San Franciscans getting hammered by norovirus, with a suspicious number of cases tracing back to oysters consumed over the weekend, particularly after last week's midweek rain. Rain runoff is a known culprit for contaminating coastal shellfish beds with bacteria and viruses, and norovirus — the ruthlessly efficient stomach bug that tears through populations like a wildfire — appears to be the unwelcome guest at this particular dinner party.

One local described the scene with vivid economy: "A healthy, normal-looking gentleman got off my bus yesterday and started projectile vomiting repeatedly on the sidewalk, so I have to assume norovirus is going around." Lovely. Welcome to San Francisco, where the street hazards now include biological warfare from bivalves.

Several residents reported a nearly identical timeline — oysters on Sunday, full-blown gastrointestinal misery by Monday morning. One SF parent noted their adult son "ate an oyster Sunday night and had gastrointestinal problems starting Monday morning." Others who didn't eat shellfish at all reported similar symptoms, suggesting the virus may already be spreading person-to-person.

Here's the thing that should bother you: after heavy rains, the risk of shellfish contamination spikes. This isn't new science. So where's the public health advisory? Where's the Department of Public Health getting ahead of this with alerts to restaurants and consumers? We spend enormous sums on our city's public health infrastructure, and yet San Franciscans are left to crowdsource their own outbreak investigation online.

As one chastened resident put it: "TIL you shouldn't eat oysters year-round. I've just been getting lucky." The old rule of thumb — only eat oysters in months with an "R" — exists for a reason, folks.

Bottom line: if you're going to gamble on raw shellfish after a rainstorm, at least know the odds. And maybe our well-funded health agencies could do their jobs and issue a timely warning before half the city is down for the count.