Comparable Norovirus Shedding in Symptomatic and Asymptomatic Individuals: A Hospital-Based Study in Bangladesh

The frequent detection of norovirus in the stool of healthy people may be due to prolonged norovirus shedding after recovery from illness or asymptomatic infections. We describe norovirus shedding patterns in symptomatic and asymptomatic persons in Bangladesh.

We enrolled acute gastroenteritis (AGE) cases and non-AGE controls from 2 hospitals from January to September, 2023. Fecal samples were tested for norovirus by rapid antigen testing and confirmed by real-time reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Positive persons were retested at days 20, 40, 60, and 120 by RT-qPCR. Shedding duration was calculated as the number of days from enrollment to the midpoint between the last norovirus-positive and first norovirus-negative specimens. Cycle threshold (Ct) values served as an inverse proxy for the viral load.

Among 16 persons confirmed infected with norovirus (11/32 AGE cases; 5/28 non-AGE controls), a total of 74 stool samples were collected from enrollment through follow-up, of which 28 (38%) were norovirus positive. Of these, 20 (71%) were typed as GII.4 Sydney[P16], 1 as GII.3[P16], and 7 as GII untypeable. The median duration of norovirus shedding was similar between AGE cases (10 days, interquartile range [IQR], 9.5-29 days) and asymptomatic controls (9.5 days, IQR, 9.5-49 days). Norovirus Ct values varied substantially between persons and overlapped significantly among AGE cases and non-AGE controls.

Norovirus shedding quantity and duration were similar between AGE cases and asymptomatic controls, complicating the attribution of norovirus infection to AGE in Bangladesh. Larger longitudinal studies would more accurately characterize norovirus shedding in resource-limited settings.