As the most common inflicted pathogen causing AGE in children, several biomarkers have been developed and available commercially for the detection of rotavirus. The widely available biomarker platform utilized is the enzyme immunoassay (EIA) to screen for the rotavirus antigen
[1][2][4][6][10][13][17][85][86][87]. Amongst EIA kit used were Premier Rotaclone, Meridian Bioscience Inc., Cincinnati, OH, USA
[1][2][3][10][86][87], RIDASCREEN Rotavirus R Biopharm AG, Darmstadt, Germany
[6][86], and ProSpect Rotavirus Test, Oxoid Ltd., UK
[13][86]. Rotavirus antigens can also be detected by using enzyme-linked immunosorbent assay (ELISA)
[3][7][9][11][19][22] which includes ELISA kits such as Premier Rotaclone, Meridian Bioscience, Inc.
[3], Fecal Rotavirus Antigen ELISA Kit (EDI, CA, USA)
[7], ProSpecTM Rotavirus Microplate Assay, Oxoid
[11] and Rota Antigen Test Device, Cambridge
[19]. ELISA can also be used in the detection of rotavirus-specific IgM
[21]. Other methods in detection of rotavirus antigen were immunochromatography
[16][18] and latex agglutination
[14][85][88]. In addition, polyacrylamide gel electrophoresis (PAGE) was carried out to determine the electropherotype of rotavirus strains
[1][10][85]. Moreover, samples that were rotavirus positive for ELISA or EIA were sent for genotyping using reverse-transcription polymerase chain reaction (RT-PCR) to determine whether they belong to particular G/P genotypes
[2][7][10][11][16][21][89][90]. A multiplex real-time RT-PCR is an advanced approach for a high-throughput rotavirus genotype characterization for monitoring circulating rotavirus wild-type strains, which is more robust in identifying a novel strain
[91].
2.2. Norovirus
Viral RNA and antigens are the main biomarkers for detection of norovirus infection. Real-time quantitative polymerase chain reaction, Multiplex Gastrointestinal Platforms, enzyme immunoassays (EIAs) and genotyping are the main methods used in laboratory diagnosis of norovirus
[92]. Cepheid Xpert
® Norovirus kit automates sample processing, nucleic acid extraction, and real-time reverse transcription polymerase chain reactions (RT-PCRs) for detection and differentiation of norovirus GI and GII, which account for the majority of norovirus infections worldwide
[93][94]. Another real-time PCR platform, RIDA
®GENE Norovirus, can also be used as an alternative in detecting the virus
[95]. Although PCRs are highly sensitive and specific, they are expensive and require specialized techniques and equipment. Rapid diagnostic tests are usually carried out during outbreak screening and patient management, which include immunochromatographic test, enzyme immunoassay (EIA), enzyme-linked immunosorbent assay (ELISA) and fluorescence immunoassay (FIA). RIDA
®QUICK Norovirus (R-Biopharm AG, Darmstadt, Germany) is one of the most used rapid immunochromatographic tests to detect norovirus
[96][97][98]. Other immunochromatographic tests that are still used include QuickNaviTM—Norovirus 2
[99][100]. RIDASCREEN
® Norovirus 3rd Generation is an example of ELISA that is still currently in use
[101][102]. For FIA, the Automated Fluorescent Immunoassay System NORO (AFIAS-Noro) assays (Boditech Med Inc, Gangwon-do, South Korea) are newly developed diagnostic tests for norovirus infections
[88].
2.3. Astrovirus
Stool samples can be investigated using RT-PCR to detect the presence of human astrovirus (HAstV)
[39][40][47]. One of the available kits is the RT-PCR Luminex Assay, with which a portion of the ORF2 capsid region is targeted by using a set of specific reverse primers labeled with biotinTEG at 5′-ends and specific probes sequences
[103]. A one-step, accelerated, real-time RT-LAMP (rRTLAMP) assay can also be used by targeting the 5′-end of the capsid gene for rapid and quantitative detection of HAstV
[104][105].
2.4. Enteric Adenovirus Serotypes 40 and 41
Adenovirus antigen and hexon-coding gene in enteric adenovirus serotypes 40 and 41 can be recognised and used for screening and detection methods of this pathogenic agent infection. BioNexia RotaAdeno and RIDA Quick Rota-Adeno-Combi R-Biopharm, which are the immunochromatographic tests (ICT) and LIAISON Adenovirus chemiluminescence immunoassays (CLIA) can be utilised to detect enteric adenovirus antigen
[106][107]. The samples from ICT and LIAISON CLIA can subsequently undergo RT-PCR for genotyping of hexon-coding genes by using a specific TaqMan Array Card, which is a 384-well singleplex real-time PCR format that has been recognised to detect multiple infection targets
[108][109].
2.5. Salmonella
As for
Salmonella infection, the virulence genes include flagellin (
filcC),
invA,
invF,
sitC,
hilAgene,
sipC,
sipF genes as well as heat stable enterotoxin gene,
parE [110]. Multiplex real-time PCR such as RIDA GENE-gastrointestinal kits, EntericBio real-time Gastro Panel I, and Seeplex Diarrhea ACE detection has allowed a more rapid detection of multiple targets in a short period of time and some of the tests was followed by hybridisation to microarray/macroarray to achieve multiparametric detection of AGE aetiological agents
[111]. In terms of sensitivity and specificity, RIDA GENE-gastrointestinal kits were reported to have 25% sensitivity and 99.7% specificity
[112][113][114]. As for EntericBio real-time Gastro Panel I, its sensitivity and specificity were much higher, which were 100% and 97.8%, respectively
[113]. Seeplex Diarrhea ACE has a sensitivity of 40–100% and specificity of 96–100%
[112][115][116].
2.6. Escherichia coli
Most of the current omics approaches were focused on the detection of Shiga Toxin-producing
Escherichia coli (STEC) infections. This is due to the fact that accurate diagnosis of STEC infection is very crucial because appropriate early treatment decreases the risk of serious complications and improves overall patient outcome, especially in children
[117][118]. Although non-O157 serotypes account for the majority of STEC infections, they are significantly under-reported because frontline microbiology laboratories mainly focus on the detection of O157 STEC using specific agar-based methods
[119]. CHROMagar STEC is a new chromogenic medium invented to improve detection of STEC, which detects O157 and non-O157 STEC through a chromogenic substrate
[119][120]. However, PCR is a more sensitive test than culture
[119][120]. RIDA
®GENE real-time PCR kits EAEC, EHEC/EPEC, and ETEC/EIEC (R-Biopharm, Darmstadt, Germany) all can be used to detect the
aatA and
aggR,
eae, and
elt and
estA genes of Enteroaggregative, Enteropathogenic, and Enterotoxigenic
Escherichia coli, respectively
[121]. These will ensure that different pathotypes of diarrheagenic
Escherichia coli can be detected and differentiated successfully.
2.7. Entamoeba histolytica
Entamoeba histolytica infection can cause a significant decrease in serum leptin and has been suggested to be a potential biomarker for this pathogenic infection
[122], which can be detected using the ELISA technique (kit supplied by RayBiotech.Inc, Guangzhou, China). Moreover, there was also a marked increase in HDL, obestatin, calprotectin and SIgA concentration level with a concurrent decrease in cholesterol, triglyceride, LDL and VLDL concentration levels. All of these serums can be analysed and measured using ELISA techniques
[123]. ELISA (Techlab II
Entamoeba histolytica) can also be used to detect
Entamoeba histolytica antigen presented in stool with a specificity of 100% but with a low sensitivity of 19.2%
[124]. Thus, multiplex PCR is a more favourable option as it has sensitivity of 100% with specificity of 95.8%
[125]. During progression of amoebiasis, a small non-coding RNA known as microRNA (miRNA) is involved in promoting apoptosis in epithelial colon cells and comprehensive profiling of miRNA using Taqman Low-Density Arrays showed a significant interaction between miRNA and parasite presented
[126]. Taqman Low-Density Arrays has a sensitivity of 92% and a specificity of 100% in diagnosis of
Entamoeba histolytica infection
[127].