https://www.yahoo.com/news/us/articles/dozens-hikers-suddenly-fall-sick-211249845.html

> norovirus

Interesting. The most common water treatment method on the trail is a 0.1 micron Sawyer filter. That handles parasites like giardia, bacteria like salmonella and so forth, but of course does not handle viruses.

Some people use UV treatment, which kills everything, but doesn't filter out sediment and similar contaminants.

> drinking from sealed water bottles.

Which may be the most useless hygiene advice ever given to hikers. Let me just carry 5 gallons in sealed bottles for the next 100 miles of trail.

The military used to have water treatment (chemical) tabs for troops in the field, probably still do, but I don't know what bugs they kill.  Still better than nothing.

In an emergency, iodine, so many drops per gallon, will add some protection but I forget the ratio.

You can still get treatment tans and iodine. They kill everything, but most people don't like the aftertaste, iodine stains and you have to wait to drink.

We keep a couple in our emergency kit. But for people on the trail for 100 days, it's rare to use them. Of course, if norovirus is a big issue...

That said, there are some studies that show that people who get sick on the trail usually bring the bugs with them. It's usually one person in the party who has a toddler in daycare.

So we now prioritize hand washing over water filtration. Obviously we try to do both, but a small drink from a high Sierra creek in spring flow is almost guaranteed safe. Having dinner in a group of four and sharing food and pots? Not so much. People often let hand hygiene slip on the trail.