Rachel M. Burke
Surveillance data show that norovirus outbreaks caused by a single genotype, GII.4, and those occurring in health care facilities include higher rates of severe outcomes — findings that should guide vaccine development, researchers said.
“The CDC linked information from two different surveillance systems to analyze 3,747 norovirus outbreaks reported by health departments from 2009 to 2016,” Rachel M. Burke, PhD, MPH, an epidemiologist in the CDC’s Viral Gastroenteritis Branch, told Infectious Disease News. “Our study provides a comprehensive description of norovirus outbreaks from the epidemiology and laboratory perspectives, using the National Outbreak Reporting System and CaliciNet, respectively.”
Burke and colleagues analyzed the data to determine differences in genotype, hospitalization and mortality rates.
Most outbreaks — 62.8% (n = 2,353) — were caused by the GII.4 genotype. These outbreaks were associated with health care settings (OR = 3.94; 95% CI, 2.99-5.23); the months of November through April, encompassing winter (OR = 1.55; 95% CI, 1.24-1.93); and older age, with at least 50% of patients aged 75 years or older (OR = 1.37; 95% CI, 1.04-1.79). GII.4 outbreaks also were more likely to result in severe outcomes (hospitalization rate ratio = 1.54; 95% CI, 1.23-1.96; mortality RR = 2.77; 95% CI, 1.04-5.78), as were outbreaks that occurred in health care settings (hospitalization RR = 3.22; 95% CI, 2.34-4.44; mortality RR = 5.65; 95% CI, 1.92-18.70).
“To prevent the most severe outcomes from norovirus, future vaccines should provide protection against GII.4, and potentially target individuals in health care settings,” Burke said. “Health care providers should be vigilant for possible severe outcomes from norovirus outbreaks in health care settings, outbreaks caused by GII.4, and when novel GII.4 strains emerge.
“The best ways to protect against norovirus are to wash hands often; clean and disinfect surfaces with bleach; rinse fruits and vegetables and cook shellfish thoroughly before eating; and when sick, stay home and don’t prepare food for others until 2 days after symptoms stop.”
In a related editorial, Geoffrey A. Weinberg, MD, professor of pediatrics and clinical director of the Pediatric Infectious Diseases & Pediatric HIV Program, at the University of Rochester School of Medicine & Dentistry and Golisano Children’s Hospital, wrote that Burke and colleagues “present new findings on the ‘epidemiologic triad’ affecting norovirus disease outbreaks — the triad being comprised of viral, host, and environmental factors. Their data confirm that the notion of noroviruses simply being ‘a cruise ship virus’ or an occasional foodborne winter vomiting illness is outdated.”
“Today, the leading nonbacterial (viral) acute gastroenteritis across the globe are much better defined than they were in the past; the majority of acute gastroenteritis is caused by rotaviruses and noroviruses, and because of the effectiveness of rotavirus vaccination, there is an ongoing shift in proportions of disease caused by each,” Weinberg told Infectious Disease News. “Now, in the [United States] and in other areas, noroviruses are very likely to be the leading cause of acute gastroenteritis.” – by Bruce Thiel
Disclosures: The authors report no relevant financial disclosures.