Norovirus (NoV) is considered as the major cause of acute gastroenteritis in both children and adults in community-based gastroenteritis, resulting in >267 000 000 annual infections worldwide [1, 2]. The virus is transmitted via food/water and person-to-person spreads [1]. When outbreaks of diarrhea occur, rapid detection of the causative virus is essential. For this reason, rapid and sensitive diagnostic tools, such as immunochromatography (IC) test, is required. Several IC kits for rapid detections of the viruses associated with diarrhea such as rotavirus, norovirus, adenovirus and astrovirus have been developed [3–5]. In this study, we evaluate three commercially available IC test kits (GE test Noro Nissui, Nissui Pharmaceutical Co. Ltd.; ImmunoCatch-Noro, Eiken Chemical Co. Ltd.; and Quick Navi-Noro 2, Denka Seiken Co. Ltd., Japan) with reverse transcriptase-polymerase chain reaction (RT-PCR) and sequencing as standard reference tests.
The NoV-positive stool samples, identified during 2011–12 in Japan, were tested. In addition, samples that were positive for other viruses (rotavirus, sapovirus, astrovirus, enterovirus, bocavirus and parechovirus) as well as negative stool samples had been randomly selected and tested. A total of 50 stool samples were included in this study. The presence of NoV as well as other diarrheal viruses in fecal specimens was detected by RT-PCR using the protocols described previously [6–8]. All of the NoV-positive samples were characterized further for their genotypes by direct DNA sequencing. Genotypes of NoVs were preliminarily assigned using a Web-based NoV genotyping tool [9].
The positive tests of ImmunoCatch-Noro, Quick Navi-Noro 2 and GE test Noro Nissui kits are shown in Fig. 1. From a total of 50 stool samples, 30 samples were confirmed as NoV positive. It was found that three genotypes were detected, namely, GII.3, GII.4 and GII.14. Two samples of mixed infection between human bocavirus (HBoV) with GII.4 and GII.14 were detected (Table 1). In addition, 20 specimens were included as non-NoV samples.
F
ig
. 1.Open in new tabDownload slideResults of NoV detections by ImmunoCatch-Noro (A), Quick Navi-Noro 2 (B) and GE test Noro Nissui (C).
T
able
1 NoV IC.
ImmunoCatch-Noro.
Quick Navi-Noro 2.
GE test Noro Nissui.
Sensitivity (%) 96.7 96.7 93.3 Specificity (%) 100 100 100 Positive predictive value (%) 100 100 100 NoV IC.
ImmunoCatch-Noro.
Quick Navi-Noro 2.
GE test Noro Nissui.
Sensitivity (%) 96.7 96.7 93.3 Specificity (%) 100 100 100 Positive predictive value (%) 100 100 100.
Positive/Negative.
Positive/Negative.
Positive/Negative.
NoV GII.3 (n = 2) 2/0 2/0 1/1 NoV GII.4 (n = 24) 23/1 23/1 23/1 NoV GII.4 + HBoV (n = 1) 1/0 1/0 1/0 NoV GII.14 (n = 2) 2/0 2/0 2/0 NoV GII.14 + HBoV (n = 1) 1/0 1/0 1/0 Non-NoV (n = 20) 0/20 0/20 0/20 Total (n = 50) 29/21 29/21 28/22.
Positive/Negative.
Positive/Negative.
Positive/Negative.
NoV GII.3 (n = 2) 2/0 2/0 1/1 NoV GII.4 (n = 24) 23/1 23/1 23/1 NoV GII.4 + HBoV (n = 1) 1/0 1/0 1/0 NoV GII.14 (n = 2) 2/0 2/0 2/0 NoV GII.14 + HBoV (n = 1) 1/0 1/0 1/0 Non-NoV (n = 20) 0/20 0/20 0/20 Total (n = 50) 29/21 29/21 28/22 Open in new tabT
able
1 NoV IC.
ImmunoCatch-Noro.
Quick Navi-Noro 2.
GE test Noro Nissui.
Sensitivity (%) 96.7 96.7 93.3 Specificity (%) 100 100 100 Positive predictive value (%) 100 100 100 NoV IC.
ImmunoCatch-Noro.
Quick Navi-Noro 2.
GE test Noro Nissui.
Sensitivity (%) 96.7 96.7 93.3 Specificity (%) 100 100 100 Positive predictive value (%) 100 100 100.
Positive/Negative.
Positive/Negative.
Positive/Negative.
NoV GII.3 (n = 2) 2/0 2/0 1/1 NoV GII.4 (n = 24) 23/1 23/1 23/1 NoV GII.4 + HBoV (n = 1) 1/0 1/0 1/0 NoV GII.14 (n = 2) 2/0 2/0 2/0 NoV GII.14 + HBoV (n = 1) 1/0 1/0 1/0 Non-NoV (n = 20) 0/20 0/20 0/20 Total (n = 50) 29/21 29/21 28/22.
Positive/Negative.
Positive/Negative.
Positive/Negative.
NoV GII.3 (n = 2) 2/0 2/0 1/1 NoV GII.4 (n = 24) 23/1 23/1 23/1 NoV GII.4 + HBoV (n = 1) 1/0 1/0 1/0 NoV GII.14 (n = 2) 2/0 2/0 2/0 NoV GII.14 + HBoV (n = 1) 1/0 1/0 1/0 Non-NoV (n = 20) 0/20 0/20 0/20 Total (n = 50) 29/21 29/21 28/22 Open in new tabTo evaluate sensitivity, specificity and positive predictive value, the same set of 50 samples was tested by three IC kits and the results were compared with those obtained by RT-PCR (Table 1). Of the 30 samples that were positive for NoV by RT-PCR, 29, 29 and 28 were detected by the ImmunoCatch-Noro, Quick Navi-Noro 2 and GE test Noro Nissui test kits, respectively. These results indicated 96.7, 96.7 and 93.3% of the sensitivity. For the 20 non-NoV samples, all showed negative results in agreement with RT-PCR. These data indicate that the specificity and positive predictive values were equal at 100% for all test kits.
Because of a lack of tissue culture system for NoV, detection of NoV is therefore based mainly on RT-PCR and sequencing. However, those molecular assays are time-consuming and more expensive. To meet these needs, easy-to-perform tests, such as IC tests, have been developed. For these three IC kits, one false negative was observed by ImmunoCatch-Noro and Quick Navi-Noro 2, while two false negative were observed by GE test Noro Nissui. The discrepancy might be due to a low viral load in stool specimens. To clarify this point, additional testing with large number of samples and with known viral copy number may need to be performed. In conclusion, our study demonstrated that the IC kits could be used as an alternative method for detection of NoV in stool specimens especially during outbreak seasons. In addition, the sensitivity of the IC test kits should be improved before using these kits for the routine diagnostic purpose.
This research was supported by grants-in-aid from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and the Ministry of Health, Labour and Welfare, Japan.
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