Researchers from the Centers for Disease Control and Prevention carried out the largest systematic review and meta-analysis to date on noroviruses and acute gastroenteritis, and found the estimates are higher than previously thought, highlighting the need for norovirus vaccines.
They publish their results in The Lancet Infectious Diseases.
Gastroenteritis is an infection of the gut that involves vomiting, diarrhea, stomach cramps, aching limbs or fever. According to the study authors, gastroenteritis causes the second greatest burden of all infectious diseases worldwide, estimated at 89.5 million disability-adjusted life-years (DALYs) and 1.45 million deaths globally each year.
Though low-income countries are most affected by the infection - more than 25% of deaths in children under 5 years are attributable to acute gastroenteritis in Africa and southeast Asia - in the US, acute gastroenteritis as a result of norovirus causes roughly 70,000 hospitalizations and 800 deaths each year.
The prototype norovirus, known as Norwalk virus, was first identified in 1972 from an outbreak of acute gastroenteritis at an elementary school in Norwalk, OH. During this time, 50% of the students and teachers were infected in 2 days, demonstrating how quickly norovirus outbreaks can spread.
Lead study author Dr. Benjamin Lopman, from the Centers for Disease Control and Prevention (CDC), explains further:
"Norovirus spreads from person to person and through contaminated food or water and contact with contaminated surfaces. The virus is so contagious that as few as 18 viral particles may be enough to infect a healthy person, while more than a billion viruses can be found in a single gram of an infected person's stool."
He adds that, currently, there is no norovirus vaccine or treatment.
Estimates higher than previously thought
To further investigate the prevalence of norovirus in individuals with acute gastroenteritis, Dr. Lopman and his team analyzed 175 published reports from 1990-2014.
Norovirus was found in cases of gastroenteritis in developing countries, such as Africa, at 14-19%, but it was also found at 20% in developed nations.
Overall, they found that noroviruses are responsible for 18% of acute gastroenteritis cases worldwide, across all age groups.
In detail, they also discovered that norovirus was more common in cases of acute gastroenteritis in the community (24%) and outpatient (20%) settings than in emergency department visits and hospitalizations (17%).
The team says this supports the idea that norovirus is a more common cause of mild disease.
Additionally, norovirus was found in cases of gastroenteritis in developing countries - at 14-19% - and in developed nations - at 20%. As such, the team says this shows that norovirus cannot be controlled by simply improving water and sanitation.
Though previous reviews have endeavored to make accurate estimates, the researchers say their review "included more than five times as many studies from almost twice as many countries than did a similar review based on the data available less than 5 years ago."
With their fuller evidence and more precise estimates, the researchers point to the need for a solution to the problem. Dr. Lopman says:
"Our findings show that norovirus infection contributes substantially to the global burden of acute gastroenteritis, causing both severe and mild cases and across all age groups. Diarrhea remains one of the leading causes of death of children in developing regions of the world. We have much to learn about norovirus in those settings, and how it can best be controlled."
Limitations prompt need for further study
The team used data from 48 countries involving more than 187,000 cases of gastroenteritis.
However, in a linked comment, Dr. Ulrich Desselberger and Prof. Ian Goodfellow, from the University of Cambridge in the UK, point to some limitations of the study.
Firstly, they point to "inconsistent age stratification across studies," which prevented a full analysis of the burden in people aged 65 or older. They add that this age group is typically more susceptible to complications from the virus and are at a greater risk of death, as a result.
Additionally, they say that many countries have not conducted an in-depth investigation into the prevalence of noroviruses, which may mean the burden estimates are not entirely reliable.
"Therefore," they write, "additional high quality studies in these settings will be crucial to improve disease estimates."
Medical News Today recently covered a report from the CDC that suggested in the US, most norovirus outbreaks from contaminated food happen in restaurants, giving many diners reason to pause before eating out.