Because norovirus can spread so rapidly under certain environments and conditions (the classic “cruise ship bug” example), and because current methods of diagnosis require stool or blood collection, a minimally invasive and rapid test that can detect infection and identify genotype could help with rapid diagnosis and help clinicians control outbreaks much sooner, before they reach epidemic proportions.
Investigators at the Johns Hopkins Schools of Public Health and Medicine have developed a saliva-based assay that correctly detected the infecting norovirus genotype with 96% specificity compared with polymerase chain reaction (PCR)-diagnosed norovirus infections. Their findings
appeared in The Journal of Infectious Diseases
earlier this month.
“Saliva collection is minimally invasive, does not require clinical personnel, and can be implemented easily in any setting including remote areas and community-based settings,” investigators reported in the study. “Saliva harbors pathogen-specific immunoglobulin A and immunoglobulin G antibodies, and immunoassays based on saliva can detect pathogen exposure with similar sensitivity and specificity as blood-based immunoassays in adults.”
Norovirus, was responsible for an estimated 19 to 21 million cases of acute gastroenteritis (AGE) in the United States last year. Currently, methods of diagnosis include stool or blood collection, both of which can present difficulty in non-clinical settings.
“Stool sample collection and testing is a feasible method in clinical settings where patients with severe AGE present seeking care; however, patients and family members are inconvenienced by stool collection and handling and often do not provide appropriate samples,” investigators determined. “An alternative approach to diagnose infection is measuring pathogen-specific antibody levels in blood. But blood collection is invasive, usually requires clinically trained personnel, and has practical constraints among young children.”
The new saliva-based assay measures the salivary immunoglobulin G responses to the 5 most common norovirus genotypes (GI.1, GII.2, GII.4, GII.6, and GII.17). Investigators tested acute and convalescent saliva samples from Peruvian children younger than 5 who had already been positively diagnosed via PCR. Their method correctly identified norovirus infection and correctly assigned genotype with 71% sensitivity and 96% specificity.
“This is, to our knowledge, the first study to systematically validate a salivary norovirus assay for its performance to (1) identify norovirus infection among children with known infection status in a highly endemic setting and (2) discriminate the 5 most common genotypes using saliva samples from children <5 years of age,” investigators wrote.
“Future studies should investigate if a salivary anti-norovirus immunoglobulin A assay could be used to identify acute infection without the need for repeat sampling. Salivary immunoassays to monitor norovirus infections at the genotype level could be implemented in epidemiological studies in community settings, in outbreak investigations, and in high-risk settings such as schools or health care facilities to monitor transmission,” they concluded.
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