Norovirus, a highly contagious disease that causes vomiting and diarrhea, has increased in the Northeast region of the United States in the past few weeks. CDC statistics show that food is the most common transmission vehicle for noroviruses.

Surveillance data shows a nationwide spike in positive test results — as is common for norovirus during the winter months — with northeastern states particularly hit hard, with a three-week average for positive norovirus tests of 13.7 percent. As of December 2023, those tests had a positive rate of more than 10 percent.

Other U.S. states have also seen modest increases in norovirus cases. For the past three weeks, the South has seen a positive test rate of 9.4 percent, the Midwest at 10 percent, and the West at 12.6 percent.

What is norovirus?

The Centers for Disease Control and Prevention (CDC) estimates that noroviruses cause approximately 21 million cases of acute gastroenteritis each year, making norovirus the leading cause of gastrointestinal disease in adults in the United States.

Nature made a clever mistake in norovirus. The round blue ball structure of norovirus is a protein that surrounds the genetic material of the virus. The virus attaches itself to the cells in the intestine and then transfers its genetic material to these cells. After transferring its genetic material, norovirus replicates, eventually killing human cells and releasing new copies, which attach to more cells in the gut.

Humans are the only host of norovirus, which has many mechanisms that allow it to spread quickly and easily. Norovirus affects people in a similar way to an influenza virus infection. In addition to their similar routes of infection, norovirus and influenza also evolve to evade the immune system in similar ways. Both viruses are subject to severe immune selection pressure and antigenic drift, which allows the immune system to evade them, resulting in epidemics. Norovirus can survive at different temperatures and in different environments. Moreover, viruses can spread quickly, especially in close proximity to people, such as cruise ships and airline flights, even for short periods of time.

How is norovirus transmitted?

Norovirus causes nearly 60 percent of all foodborne illness outbreaks. Norovirus is primarily transmitted through the fecal-oral route, and fewer than 100 tiny norovirus particles are needed to cause infection. Transmission occurs from person to person or through contamination of food or water. Of the 232 norovirus outbreaks from July 1997 to June 2000, 57 percent were foodborne, 16 percent were person-to-person, and 3 percent were waterborne. When food is a transmission vehicle, contamination occurs directly through the food handler before eating the food.

People infected with the virus shed more virus particles in their saliva and secretions when they are sick. Aerosolized vomit has also been implicated as a mode of transmission of norovirus. Previously, it was thought that viral shedding stopped 100 hours after infection; However, some individuals continue to shed norovirus long after recovery, in some cases up to 28 days after symptoms appear. It may also precede the symptoms of viral shedding, which occurs in about 30 percent of cases. Often, contaminated food may not even show signs of infection.

What are the symptoms and risks of norovirus infection?

Norovirus disease usually develops within 24 to 48 hours after ingestion of contaminated food or water. The symptoms usually last for a relatively short period of 24 to 48 hours. These symptoms are nausea, vomiting, diarrhea and abdominal pain. Headache and low-grade fever can accompany this disease. People infected with norovirus usually recover within two to three days without serious or long-term health problems.

Although symptoms usually last one to two days in healthy people, norovirus infection can be serious in children, the elderly, and people with weakened immune systems. In some cases, norovirus infection can cause severe dehydration, malnutrition, and even death, especially in children and older, immunocompromised adults in hospitals and nursing homes.

How do you diagnose a norovirus infection?

Diagnosis of norovirus disease is based on a combination of symptoms, especially the prominence of vomiting, low fever and short duration of illness. If a known norovirus outbreak is underway, public health officials may obtain samples from sick people for laboratory testing. These laboratory tests include detecting norovirus under an electron microscope.

How to treat norovirus infection?

There is no specific treatment for norovirus. In most healthy people, the pain is self-limiting and resolves within a few days; But outbreaks among infants, children, the elderly, and immunocompromised populations can cause serious complications for those affected. It can cause death without taking immediate measures. It’s important to replace fluids and minerals like sodium, potassium, and calcium — otherwise known as electrolytes — that are lost due to persistent diarrhea. This can be done by drinking large amounts of fluids or through blood.

How to prevent norovirus infection?

Common norovirus outbreaks include restaurants and events (36 percent), nursing homes (23 percent), schools (13 percent), and vacation or cruise ships (10 percent). The best way to prevent the spread of norovirus is to wash your hands.

Shellfish (oysters, clams, mussels) pose the greatest risk. Any service can be contaminated with norovirus; There is no way to reliably identify an infected oyster, clam, or mussel. Shellfish become infected when their water is contaminated with:example (when raw sewage is dumped by recreational or commercial boats). Shellfish are filter feeders and concentrate virus particles in their environment. With shellfish, only thorough cooking provides reliable protection; Steaming does not kill the virus or prevent its spread.

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