Many of us have heard of the “stomach flu” but not the actual virus that causes it: Norovirus. Norovirus has been in the news lately when a long-term outbreak occurred among more than 220 rafters and hikers in the Grand Canyon National Park from April to mid-June of this year. Less well known is 448 norovirus cases reported in the U.S. from Aug 2021 to March of this year. That was six times the number of cases reported during the same time the year before.
We personally an experience with the virus a few years ago when my wife sampled “The World’s Best Hot Dog” at a street stand in New York City while visiting our daughter. Believe me, it’s no fun, and considering that norovirus can be found everywhere from the Big Apple to the Grand Canyon, the family medic should know about it.
The National Foundation for infectious diseases reports that noroviruses are the most common cause of acute stomach and intestinal infections in the United States, The U.S. reports 19 million to 21 million cases a year. Humans are, apparently, the only hosts of the virus. It affects people of all ages, but it’s particularly dangerous in the elderly, the very young, and those with weakened immune systems. Except for this year, winter is the most common time for outbreaks.
The virus was formerly known as the Norwalk virus because the first known outbreak took place at an elementary school in Norwalk, Ohio. Scientists identified the virus in 1972 from stool samples and renamed it “norovirus.” Since then, it’s been identified everywhere from cruise ships to nursing homes.
Norovirus is very contagious (just 5-20 viral particles can cause illness) and is easily transmitted through contaminated food or water, close personal contact, and even by air droplets from vomit, contaminated kitchen counters, and even toilet flushes. Infection can be passed from person to person for a time even after apparent recovery.
Here’s how contagious the norovirus is: In one outbreak reported in 1998, 126 people were dining at a restaurant when one person vomited onto the floor. Despite a rapid cleanup, 52 customers fell ill within three days. More than 90% of the people who later dined at the same table reported symptoms. More than 70% of the diners at a nearby table got sick; at a table on the other side of the restaurant, the rate was still 25%.
Norovirus is a hardy microbe, and is known to survive for long periods outside a human host. It can live for weeks on countertops and up to twelve days on clothes. It can survive for months in still water. Disinfectants containing chlorine, however, like bleach will quickly eliminate it, as will sufficient heat.
SYMPTOMS OF “STOMACH FLU”
The symptoms of the stomach flu include nausea and vomiting, watery diarrhea, and (sometimes severe) abdominal pain, usually within 12 to 48 hours of exposure. Along with this, muscle aches, headache, and fever may be seen. Luckily, life-threatening illness is rare, with dehydration being the main danger in those infected with the virus. Symptoms may last several days before eventually subsiding.
Unlike some viruses, immunity to norovirus is only temporary. Antibodies against the virus at thought to last up to six months after recovery. Also, there are various types of noroviruses, getting one doesn’t protect you against others.
Outbreaks of norovirus infection often occur in closed spaces such as cruise ships, nursing homes, schools, camps, and prisons. Shellfish, such as oysters, and salad ingredients are the foods most often implicated in norovirus outbreaks (except, of course, “the World’s Best Hot Dog”).
As is the case with most viruses, there is no known cure for norovirus infection. Antibiotics will not be effective, as they are meant to kill bacteria, not viruses. Treatment involves staying well-hydrated. Suspect dehydration if you see these signs and symptoms:
· Dry mouth
· Decrease in quantity or dark color of urine
· Dizziness when standing up
· Decreased elasticity of skin (it “tents” when pulled)
· No tears when crying or unusual irritability in infants
Using antidiarrheal meds like loperamide (Imodium) and anti-vomiting drugs like Ondansetron (Zofran) may also help.
A cure may not be available but prevention is another issue. To decrease the chance of norovirus infection:
· Wash your hands frequently with soap and water (norovirus is relatively resistant to alcohol), especially after using the restroom or handling food. Be especially sure to do this for 2 weeks after becoming infected (yes, you can be contagious for that long).
· Wash food before cooking; cook shellfish thoroughly.
· Frequently disinfect contaminated surfaces with a bleach solution (the EPA recommends 5-25 drops of bleach per gallon).
· Keep sick individuals away from food preparation areas.
· Avoid close contact with others when you are sick, and don’t share utensils or other items.
· Wear disposable gloves while handling soiled items.
· Immediately remove and wash clothes that may be contaminated with vomit or feces. Machine dry if possible.
It may be difficult to completely eliminate the risk of norovirus infection, but careful attention to hand and food hygiene will go a long way towards avoiding the stomach flu.
Joe Alton MD
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