Well, it has happened again. Nearly two hundred people have come down with intestinal illness in a US wilderness area, Yosemite National Park (https://www.sfchronicle.com/news/article/170-Yosemite-Valley-visitors-fall-fill-14982216.php).
The culprit? It appears to be norovirus, spread by hand contact. Which is not surprising, since this organism and this mode of spread are responsible for virtually all such outbreaks in the US. Granted, the bulk of these folks were staying in a hotel within the park, but they had been using other park facilities, and hiking in the area. This follow on the heels of another report, which I cited earlier, of norovirus outbreaks among Colorado River rafters.
Of note, no one reporting on this outbreak has even mentioned the possibility of water-borne infection. I was elated to see this, as it may demonstrate that folks are finally recognizing that hand to mouth spread of infection is far and away the most common method of spread anywhere. Outbreaks caused by water consumption are exceedingly rare, and mostly limited to faulty municipal water systems.
While norovirus is far and away the most common cause of epidemic vomiting and diarrhea in the US, a host of other organisms, such as giardia and E coli, are occasional causes. All of these are most commonly spread by poor hand hygiene.
If folks choose to continue to carry and use their silly water filters in the backcountry, there is probably no harm done. They just need to be sure that they also pack their soap or hand sanitizer!