Asymptomatic reservoirs a potential source of norovirus outbreaks
Asymptomatic reservoirs appear to be able to transmit large amounts of norovirus (NoV) on their stools, a recent study from Indonesia shows. Thus, this may be a potential source of NoV outbreaks.
Reverse transcription-polymerase chain reaction (PCR) was carried out in 512 stool samples obtained from 18 asymptomatic individuals (aged 20 to 42 years; 66 percent female). NoV viral load was determined using real-time PCR of viral RNA.
Of all stool samples, 14 tested positive for NoV, resulting in an overall detection rate of 2.7 percent. These samples were collected from seven different participants (38.9 percent) who did not significantly differ in sex (p=0.36), use of western toilets (p=0.36) and educational background (p=0.64) from those who did not have NoV-positive stools.
The viral loads were low for most of the positive subjects, with titres ranging from <101 to 105 copies/g.
The month with the highest NoV prevalence was determined to be July, followed by April, August and November. The remaining months had relatively low levels of NoV prevalence with the months of June, May and March having no observed infections. The interval of duration between reinfections were 1 to 4 months.
All 14 identified NoV strains from the healthy participants belonged to genogroup II (GII). Majority of the NoV strains (71.4 percent; n=10) were classified as GII.2 while 14.3 percent (n=2) were classified as GII.17. GII.4 Sydney 2012 and GII.1 were each assigned one strain.
“[O]ur findings demonstrated that asymptomatic NoV infections are common in Surabaya, Indonesia, and some of the asymptomatic individuals shed large amounts of viruses similarly to symptomatic cases, suggesting that the excretion of NoV from healthy individuals is one of the sources of NoV outbreaks,” said researchers.