Norovirus: An Old Virus Seeking New Public Health Actions

Norovirus--3D rendering

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First identified by Albert Kapikian and colleagues in Norwalk, Ohio, in 1972, Norovirus continues to cause infections and disease outbreaks in the US over 50 years later.¹ It is the most common cause of epidemic gastroenteritis, causing 19 to 21 million cases per year, and is responsible for 2.27 million outpatient visits, 465,000 emergency room trips, 109,000 hospitalizations, and 900 yearly deaths.² The virus is particularly dangerous in children under 5 years, adults over 85, and immunocompromised people. These groups have a higher risk for severe disease and are responsible for most outpatient or emergency room visits.²

Outbreak potential, transmission, and symptoms

Norovirus outbreaks are likely to become more common without definitive public health action such as a widely available vaccine. “People are traveling more, which facilitates the spread of the virus to new areas. Norovirus’ genetic diversity and rapid evolution can lead to the emergence of new strains that may cause more outbreaks. Climate change might also be playing a role in outbreak patterns and where outbreaks happen,” says Raj Dasgupta, MD, FACP, FCCP, FAASM, a board-certified physician in internal medicine, critical care, pulmonology, and sleep medicine and chief medical advisor at Sleep Advisor.

Norovirus has many nicknames, including stomach flu, gastric flu, winter vomiting virus, and the cruise ship virus. But it’s not related to the common flu caused by influenza viruses. There are several strains of the Norovirus, but they all belong to the Caliciviridae family, which consists of nonenveloped, positive-sense, single-stranded RNA viruses. They are highly contagious, and 10 viral particles can cause an infection. The primary way the virus spreads is through food-related transmission. Food contaminated by food service workers during preparation is a common source of infection. Outbreaks from eating contaminated fruits and vegetables, as are those from fish and oysters, are common. Person-to-person spread is also possible when droplets from infected people’s vomit or stools infect others. Contaminated surfaces are also part of its spread.³

The virus mutates fast, and the CDC has said new strains are responsible for 50% more infections.² “Norovirus is quite a shape-shifter,” said Dasgupta. This constant evolution means new strains pop up from time to time, which could affect how outbreaks happen and how effective preventive measures are,” he added.

Two people testing positive for the Norovirus is regarded as an outbreak. In the US, there are 2000 outbreaks yearly, most of which occur between November and April.2 Outbreaks have happened in several settings, including health facilities, cruise ships, military barracks, schools, care homes, and resorts. The incubation period for Norovirus is 12 to 48 hours, with 33 hours being the median.

The most common symptoms are nausea, vomiting, and diarrhea. But people also report body pains, headaches, abdominal pain and cramping, and chills. Fever is a less common symptom that has also been reported. Symptoms last for 1 to 3 days and may resolve on their own. Immunocompromised people, those who recently received transplants, older adults, and neonates have a higher risk of fatal illness and need extra attention.³

Prevention and control, trusted methods, and newer options

The mainstay of prevention is proper handwashing. Studies show that washing hands with soap and running water for 20 seconds is the most effective hand hygiene for eliminating the virus.³ Alcohol-based sanitizers are less effective. Though they can reduce the viral count on the hands, they are best used alongside proper handwashing.

Decontamination of surfaces also plays a vital role in infection control. During diarrhea and vomiting episodes, the virus is inadvertently sprayed into the air and on surfaces. Sinks, toilets, beds, chairs, counters, doors, faucet handles, and floors are all potential sources of infection. All potentially contaminated surfaces must be decontaminated, and any items that cannot be decontaminated must be discarded.³ The pathogen can survive on surfaces for 2 weeks. It can also survive freezing temperatures and warm water but dies when exposed to temperatures of 145 degrees Fahrenheit (62.7 degrees Celsius).

Bleach kills the virus. Five to 25 tablespoons of chlorine bleach in a gallon of water creates an effective disinfection solution that can be used to disinfect surfaces and bedding.⁴ Bipolar ionization is a newer technique that has also been used to reduce infectivity and kill the virus.

"In addition, because Norovirus can reside on touchable surfaces like a doorknob, phone, computer keyboards, handrail, or other surface that a contagious person has recently touched, adding Bipolar ionization to your home or office HVAC system can help kill surface contamination in public spaces as it continuously sanitizes surfaces thereby lessening the risk of infection," said Philip M. Tierno, Jr, PhD, professor of microbiology and pathology, NYU Grossman School of Medicine and NYU Langone Medical Center:

To control infections, people sick with Norovirus also need to be excused from work, Tierno added. Most people stop shedding the virus within 3 days, but immunocompromised people can keep shedding it in stool for months.⁵ Allowing sick people to work endangers the public. One sick person can infect hundreds because of how contagious the virus is. But it's often challenging to enforce this because many food handlers do not get paid sick leave. Lawmakers need to do more to provide legislation mandating paid sick leave for workers in the interest of public health.

What’s next for Norovirus control?

For years, the Norovirus couldn’t be cultured in laboratories, but recent advancements have allowed scientists to grow them on gut-like tissue enriched with bacteria. It is hard to culture in the lab, hindering research on killing, controlling, and detecting it. Disturbing, considering the illness costs the US 7.6 million in direct costs and 165.3 million in productivity losses each year.⁶

There’s no treatment for Norovirus yet. In most people, it is a self-limiting illness that resolves after about 3 days. The focus of care is maintaining adequate hydration and treating symptoms. Probiotics may help control diarrhea, but this is still being investigated. Extreme fluid loss is possible and can lead to complications such as dehydration, hypokalemia, hyponatremia, metabolic acidosis, hemolytic uremic syndrome, and kidney failure.³

This year, scientists reported clinical improvements in 4 immunocompromised people infected with chronic norovirus treated with favipiravir, including in combination with nitazoxanide. The drugs reduced infectivity, but more extensive studies are needed to ascertain safety and utility in larger populations.⁷

No widely available vaccine for Norovirus is available, but several contenders are undergoing clinical trials. One of the most promising candidates was created by researchers from Washington University School of Medicine, who merged recombinant forms of norovirus with existing rotavirus vaccine and elicited an immune response to both viruses from mice.⁸ It remains to be seen if this result can be duplicated safely and effectively in humans.

Perhaps because most people recover without incident and the annual death toll remains below 1000, Norovirus does not receive as much attention as it should. But concerted efforts to fast-track vaccine development and identify agents that reduce infectivity could be lifesaving for vulnerable groups and help reduce the enormous annual cost implications of norovirus outbreaks.

References

1. Lucero Y, Matson DO, Ashkenazi S, George S, O'Ryan M. Norovirus: Facts and Reflections from Past, Present, and Future. Viruses. 2021;13(12):2399. Published 2021 Nov 30. doi:10.3390/v13122399
2. Norovirus Burden and Trends | CDC. https://www.cdc.gov/norovirus/burden.html
3. Capece G, Gignac E. Norovirus. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513265/
4. Preventing norovirus. Centers for Disease Control and Prevention. Published May 10, 2023. https://www.cdc.gov/norovirus/about/prevention.html
5. Norovirus. National Collaborating Centre for Infectious Diseases. Published January 25, 2023. Norovirus.
6. Bartsch SM, O’Shea KJ, Lee BY. Corrigendum to: The clinical and economic burden of norovirus gastroenteritis in the United States. The Journal of Infectious Diseases (Online University of Chicago Press)/the Journal of Infectious Diseases. 2021;224(4):741. doi:10.1093/infdis/jiab197
7. Kreins A, Roux E, Pang J, et al. Favipiravir induces HuNoV viral mutagenesis and infectivity loss with clinical improvement in immunocompromised patients. Clinical Immunology. 2024;259:109901. doi:10.1016/j.clim.2024.109901
8. Kawagishi T, Sánchez-Tacuba L, Feng N, et al. Mucosal and systemic neutralizing antibodies to norovirus induced in infant mice orally inoculated with recombinant rotaviruses. Proc Natl Acad Sci U S A. 2023;120(9):e2214421120. doi:10.1073/pnas.2214421120