What is a Stool GPMP (Gastrointestinal Pathogen Panel)?
A stool Gastrointestinal Pathogen Panel (GPP or GPMP) is a multiplex molecular diagnostic test that simultaneously detects multiple bacterial, viral, and parasitic pathogens causing infectious diarrhea from a single stool specimen, providing results much faster than traditional culture methods. 1
Technology and Capabilities
The GPP uses nucleic acid amplification testing (NAAT) to detect a broad range of enteric pathogens simultaneously 1:
Bacterial pathogens: Typically 7-14 organisms including Salmonella, Shigella, Campylobacter, enterotoxigenic E. coli (ETEC), enteroaggregative E. coli (EAEC), Shiga toxin-producing E. coli (STEC), Yersinia, Vibrio, and Clostridium difficile 1, 2, 3
Viral pathogens: 3-5 viruses including norovirus, rotavirus, adenovirus, sapovirus, and astrovirus 1, 2
Parasitic pathogens: 2-4 parasites including Giardia lamblia, Cryptosporidium, Entamoeba histolytica, and Cyclospora 1, 3
Available Commercial Panels
Several FDA-approved multiplex panels exist 1:
Luminex xTAG GPP: Detects 15 pathogens (9 bacteria, 3 parasites, 3 viruses), though it notably lacks EAEC and Cyclospora cayetanensis 1
FilmArray GI Panel: Detects 22 enteropathogens with integrated system requiring only 5 minutes of sample handling and providing results in 1 hour 1, 2
BioCode GPP: Detects 17 pathogens (11 bacteria, 3 viruses, 3 protozoa) with sensitivity of 96.1% and specificity of 99.7% 3
Clinical Performance
GPP testing demonstrates significantly higher pathogen detection rates compared to traditional methods 2, 4:
In prospective studies, multiplex panels detected pathogens in 30-33% of samples versus only 8.3% by routine culture, microscopy, and antigen testing 2
Overall sensitivity exceeds 90% for most targets, with specificity of 98.5-99.7% 3, 5
Mixed infections are detected in 12.5-21% of positive samples by GPP versus only 8.3% by conventional methods 2
Critical Limitations and Pitfalls
The major concern with molecular GPP testing is that it may detect colonization rather than active infection, making clinical interpretation difficult 1:
High sensitivity can identify asymptomatic pathogen shedding, particularly in tropical settings where >50% of asymptomatic controls test positive 6
GPP testing does not allow for antimicrobial resistance characterization, which may be critical for directing therapy 1
Clinicians may need to order both culture-based and molecular tests to fully evaluate the patient and identify optimal therapy 1
When to Use GPP Testing
The Journal of Travel Medicine and IDSA guidelines recommend microbiologic testing (including GPP) in returning travelers with severe or persistent symptoms, bloody diarrhea, or mucus in stools 1:
Molecular testing is preferred when rapid results are clinically important or when non-molecular tests have failed to establish a diagnosis 1
Testing should be reserved for high-risk patients (immunocompromised, elderly, very young, pregnant) or those with signs of invasive disease 1
However, no clinical trials have demonstrated that using GPP improves patient outcomes or is cost-effective 1
Specimen Requirements
GPP panels can test stool in Cary-Blair transport medium or unpreserved stool 2, 3:
- FilmArray GI panel requires 200 μL of Cary-Blair stool 2
- Luminex GPP is FDA-cleared for 100 μL raw stool 2
- BioCode GPP accepts both unpreserved stool and stool in Cary-Blair medium 3
Public Health Considerations
All specimens testing positive for bacterial pathogens by GPP should be cultured at clinical or public health laboratories to ensure outbreak detection and investigation 1:
- Culture is required when antimicrobial susceptibility testing would affect care or public health responses 1
- Both E. coli and Salmonella infections are reportable diseases requiring notification of local public health authorities 7
Complementary Testing Still Needed
GPP does not replace all traditional methods 1, 6:
- Microscopy for helminths and intestinal protozoa remains necessary to cover the full etiological spectrum, particularly in tropical settings 6
- Specialized testing for Strongyloides may require Baermann technique or agar plate culture 1
- Antigen detection for specific parasites like Cryptosporidium and Giardia may still be performed alongside GPP 1