An area within the Angeles National Forest in the San Gabriel Mountains just east of the Los Angeles/San Bernardino County divide near Wrightwood is at the epicenter of an outbreak norovirus, similar to but apparently more intense than what is going on across much of the country.
Norovirus, caused by a stomach bug, is often referred to as the winter vomiting disease. Outbreaks are normally highest in the months from November to February, but can continue well into the spring.
Going back three decades, the lion’s share of norvovirus outbreaks, at least in the United States, have been dominated by one strain of the virus, labeled GII.4 by scientists, Last year, however, a variant GII.17 strain asserted itself, accounting for what is calculated three out of every four outbreaks in the United States in 2025.
Medical researches believe that either the virus mutated into what is now recognized as the GII.17 strain to make itself more transmissible or that withing the human population in certain areas of the globe there have been changes in their environment or lifestyles that have rendered them more susceptible to GII.17 than they were to GII.4.
It appears that GII.17 was introduced into a spring, some other water source or perhaps another place in the mountains where it is able to survive and proliferate in April or perhaps earlier. What is more certain is that along a stretch of the Pacific Crest Trail in the San Gabriel Mountains, infecting at least two dozen and maybe as many as three dozen of hikers who made their way through the area in early to mid-May. Many became moderately ill or worse. Reports are that a spot many of those infected came to in common is an area along the trail near Wrightwood where hikers flock because of the water available there.
Hikers related a rapid onset of intense and uncontrollable vomiting after drinking the water there, and an accompanying fatigue that essentially prevented them from summoning the energy to leave where they were camped. Days of exhaustion ensued in several of the cases. One hiker was so under the weather and weakened that an airlift to get that individual, whose gender was not identified, off the mountain was necessary.
The Pacific Crest Trail Association in a social media posting warned of “gastrointestinal illness” in the Wrightwood area. The San Bernardino County Department of Health was contacted, but has not yet put out an advisory, perhaps because the area in question is not frequented by many visitors and perhaps because the precise location of where the problem originates is not know. The Sentinel was informed at ten of those that came down from the mountain, as many as four days to a week after their symptoms first showed, were confirmed to have norovirus cases. Others who did not get tested until well after their exposure may have no longer been suffering with the condition.
Norovirus, perhaps even in a majority of cases, goes undetected or is indistinguishable from other forms of stomach flu or illnesses. One methodology for detecting its presence are tests on wastewater facilities through which the virus can be detected.
According to monitoring going on in various places around the country where norovirus outbreaks are common, neither California – in the major population areas of San Diego, Los Angeles or the Bay Area – or other major municipal areas elsewhere are seeing an upsurge in cases at present, according to the National Center for Disease Control. For that reason, the 24 or more cases in an isolated spot in the mountains is significant.
Norovirus – as its name states a virus rather than a bacteriological infection, is not generally a serious condition, unless the person beset with it experiences complications. Most of the afflicted recover within one to two weeks without seeking assistance from a healthcare professional.
In the case of GII.17, those who contract it at this point may have more intensive symptoms than those who in recent years encounted GII.4, in that many had previously dealt with a dose of GII.4, which gave them some level of immunity, which mitigates the symptoms. An individual who has experienced GII.4 or GII.17 would retain for a short period of time an absolute immunity from reinfection, but that immunity is relatively short-lived, and within two to three months, a reinfection in a previously infected person could recur.
Norovirus in all of its forms, not just GII.4 and GII.17 is the most common cause of food poisoning in the United States.
Vomiting, diarrhea and stomach cramps usually start 12 to 48 hours after exposure. Some people only complain of diarrhea or vomiting, but the vomiting that does occur is typically quire intense.
Those who appear to be recovered by the third or fourth day may yet be carriers of the disease and could still be spreading the affliction to others for as long as two weeks after being infected themselves.
There is no realistic treatment to overcome norovirus other than to simply ride it out, and antibiotics have no impact on a virus.
Medical professionals recommend that those infected recommend oral rehydration, but those who grow extremely dehydrated would be better served with intravenous fluids, as this bypasses the stomach, which can result in further vomiting. The warning signs of dehydration are decreased urination, dry mouth, dizziness, the sensation of crying without tears actually forming.