Norovirus, like Hannukah, is early this year. It already has hit the headlines, decimating a school in Southern California with its signature symptoms of vomiting and diarrhea, and now is touring the country at large: We have recent dispatches from Wyoming, Arlington, Va., and Santa Fe. Plus there appears to be a whopper of an outbreak on board one of those cruise ships full of whoever it is who goes on cruises, though the ship’s management is denying it.

But it’s not even winter yet. And norovirus, which is fondly known as “winter vomiting disease,” usually saves its worst for the deep cold. It became famous fast: we have known about noro only since 1968, when it knocked a bunch of school kids for a loop in Norwalk, Ohio. A Centers for Disease Control researcher saved many stool specimens from that outbreak, and when the investigative techniques had evolved sufficiently, went back to the specimens four years later. There, under a super-high-powered electronic microscope, he saw “small round structured viruses” or “SRSV” as they were tagged in the painfully cautious and literal medical literature.

These little round viruses, though, have proven all too hardy and extremely transmissible. Able to survive hours on surfaces such as door handles and desk tops, norovirus is now known to cause 23 million episodes of stomach and intestinal misery a year, resulting in 65,000 hospitalizations. Though it makes a person extremely uncomfortable for a day or two, it seldom is life-threatening—only 300 people die annually of the infection, usually the already frail elderly, for whom dehydration may prove fatal.

But wait—there’s more. Noro has only begun: it causes about 90 percent of all outbreaks of GI trouble in the U.S., and has proven polymorphously perverse in its countless ways of spreading person to person. Reports have come from cruise ships (many, many reports, including outbreaks so large and overpowering as to force ships back to dock to let customers and staff recuperate elsewhere), as well as from people who ate tainted food—the record is 364 people who consumed food from the same place. Indeed, norovirus is the lead viral cause of “food poisoning”—this is why you want the restaurant cook and staff to wash those hands, a lot, and to stay away when ill. It also has attacked U.S. soldiers in various wars, including Afghanistan and Iraq, so that a strain type has been dubbed Desert Shield strain. Its presence on the battlefield has in fact led some to worry about its potential as a weapon of bioterrorism (PDF).

In many of the outbreaks, at least 10 percent of all the people present who ate the bad food or floated on the bad cruise ship have become ill. Norovirus’s secret is simple: It takes only the tiniest amount of ingested virus to get sick: about 20 virus particles seem to do the trick. Compare this with something like HIV, where we consider “undetectable” a viral count less than 50 viral particles per millimeter of blood. And also consider this—an infected person has about 70 billion viral particles per gram of stool, enough to infect most of the world’s population if distributed thoughtfully. Plus it doesn’t clean up so easily—owing to its unusual quasi-outer membrane, alcohol (i.e., Purell and like products) may not punch it out so readily. More certain to sanitize the hands are old-school soap and water; bleach is used in hospitals or on cruise ships that have experienced an outbreak.

Symptoms usually develop a day or two after exposure, and hit suddenly and fiercely, then stick around for 24 or 48 hours. Typical is nausea and vomiting at the start, progressing to bad, though not life-threatening, diarrhea. Maybe a little fever, maybe some aches. Mostly people want to curl up and be left alone to die, but after a while suddenly realize a bite of that cold spaghetti wouldn’t taste so bad. One other problem—like influenza, colds, and other common viruses, we don’t seem to develop effective immunity from this year that will protect us when things start up again next winter. This dampens optimism for a vaccine. If our own immune response weren’t adequate to protect us year-to-year, why would a shot in the arm work? Nevertheless, several candidates are under development.

The lessons learned from this sort of public-health calamity are few. This one isn’t really about poor public-health infrastructure or global warming or man’s inhumanity to man. It just happens. It seems to be happening more often now because we can diagnose it so much more easily in the last few years than we could in the 1970s, when an electron microscope and an unnaturally patient microscopist were required.

But norovirus does serve as an important reminder that we are still at war—not with the terrorists or cyber-thieves or across political fissure lines, but with the microbial world, the world of relentless, brainless, disinterested viruses and bacteria and all the rest.

They have the numbers—trillions and quadrillions and whatever is bigger than quadrillions of them versus a few poor homo sapiens who, despite our big frontal cortex and opposable thumbs, our Rose Bowl parade pageantry and seven (eight?) words for snow, are just a way station for their ongoing smash-hit production. They use our machinery to rev up from a pinch to a zillion, then go off to get the next guy. It’s simple. They were here long before we climbed out of the tree to scoot around the veldt munching bananas, and will be here as brainless and disinterested as ever, long after we have globally warmed ourselves into oblivion.