Epidemiology of norovirus infections among diarrhea outpatients in a diarrhea surveillance system in Shanghai, China: a cross-sectional study.

Background: Norovirus is an important cause of gastroenteritis both in children and adults. In China, few studies have been conducted on adult populations. This study aimed to determine the contribution of norovirus to gastroenteritis, characterize the features of norovirus infections, compare them with other pathogens, and test the effectiveness of the surveillance system.

Methods: A citywide surveillance network on diarrhea patients was established. Samples were collected with intervals from both children and adults among diarrhea outpatients in hospitals and tested for viruses using rRT-PCR and for bacteria in CDCs. Patient information was acquired through interviews and recorded into a dedicated online system. The Pearson χ2 test, multivariate logistic regression models and discriminant models were fitted into its comparisons with the non-norovirus group and other pathogens.

Results: Norovirus was detected in 22.91% of sampled diarrhea patients. The seasonal distribution of norovirus infections was different from non-norovirus patients (p<0.001), with a half-year peak. Higher proportions of males (p=0.001, OR=1.303, 95% CI=1.110-1.529), local citizens (p<0.001) and officials/clerks (p=0.001, OR=1.348, 95% CI=1.124-1.618) were affected with norovirus when compared with non-norovirus patients. Diarrhea patients affected with norovirus featured nausea (p<0.001, OR=1.418, 95% CI=1.176-1.709) and vomiting (p<0.001, OR=1.969, 95% CI=1.618-2.398), while fewer manifested fever (p=0.046, OR=0.758, 95% CI=0.577-0.996) and abdominal pain (p=0.018, OR=0.815, 95% CI=0.689-0.965). Children were more vulnerable to rotavirus (p=0.008, OR=1.637, 95% CI=1.136-2.358) and bacteria (p=0.027, OR=1.511, 95% CI=1.053-2.169) than norovirus. There was a seasonal difference between the GI and GII genotypes (p<0.001). Officials or clerks were more easily affected with GI than GII (p=0.006, OR=1.888, 95% CI=1.205-2.958).

Conclusions: This study was based on a citywide hospital-sentinel surveillance system with multiple enteric pathogens included. Norovirus was recognized as the most prevalent enteric pathogen in Shanghai. The seasonal peak was from October to April. Males had a higher prevalence than females. Local citizens and officials/clerks were more vulnerable to norovirus than other pathogens. Compared with rotavirus and bacteria, children were less frequently affected by norovirus. Nausea and vomiting were typical of norovirus, whereas fever and abdominal pain were uncommon symptoms of this pathogen. GI and GII infections were centered in different seasons. Officials and clerks were more easily affected by GI than GII.