Norovirus transmission mediated by asymptomatic family members in households

Abstract

The transmission of human norovirus excreted from infected persons occasionally causes sporadic infections and outbreaks. Both symptomatic patients and asymptomatic carriers have been reported to contribute to norovirus transmission, but little is known about the magnitude of the contribution of asymptomatic carriers. We carried out a 1-year survey of residents of a district of Bangkok, Thailand to determine the percentage of norovirus transmissions originating from asymptomatic individuals. We screened 38 individuals recruited from 16 families from May 2018 to April 2019 for GI and GII genotypes. Norovirus was detected every month, and 101 of 716 stool samples (14.1%) from individuals with no symptoms of acute gastroenteritis were norovirus-positive. The average infection frequency was 2.4 times per person per year. Fourteen genotypes were identified from the positive samples, with GII.4 being detected most frequently. Notably, 89.1% of the norovirus-positive samples were provided by individuals with no diarrhea episode. Similar to cases of symptomatic infections in Thailand, asymptomatic infections were observed most frequently in December. We detected 4 cases of NV infection caused by household transmission, and 3 of the 4 transmissions originated from asymptomatic individuals. We also identified a case in which norovirus derived from an asymptomatic individual caused diarrhea in a family member. These results suggest that asymptomatic individuals play a substantial role in both the maintenance and spreading of norovirus in a community through household transmission.

Virus Etiology, Diversity and Clinical Characteristics in South African Children Hospitalised with Gastroenteritis

“…Due to the large disease and economic burden of noroviruses, an effective vaccine is in demand for high-risk populations, such as young children, the elderly, and immunocompromised individuals [ 11 ]. Understanding the prevalence and diversity of asymptomatic norovirus infections is also important as asymptomatic individuals may facilitate the transmission of this virus [ 12 ].…”

Spread of genetically similar noroviruses in Bangkok, Thailand, through symptomatic and asymptomatic individuals

“…AGE patients with only symptoms other than diarrhea, such as vomiting, were not included in this study. The hospital is located approximately 30 km from the Klong Toei district, where the community survey was conducted ( Phattanawiboon et al., 2020 ). Specimens from minors were obtained with the consent of their parent(s) or guardian(s).…”

“…The second PCR products were run on an agarose gel and purified using NucleoSpin Gel and PCR Clean-up (Macherey-Nagel, Dueren, Germany). The primer sequences used were described previously ( Phattanawiboon et al., 2020 ). The nucleotide sequence of the PCR product was determined using sequencer Model 310 (Applied Biosystems, Foster City, CA, USA).…”

“…The copy numbers of NV in the stool specimens were determined by real-time RT-PCR as described previously ( Phattanawiboon et al., 2020 ).…”

“…A meta-analysis of epidemiological studies of healthy individuals showed that asymptomatic NV infections occur in a population of individuals ( Qi et al., 2018 ). In our recent study of residents of a community in Bangkok, nearly 90% of NV infections detected were derived from individuals who had not experienced an episode of diarrhea within the past month ( Phattanawiboon et al., 2020 ). The study identified GII.4 as the most common genotype in asymptomatic individuals.…”