Detection of a Vibrio paracholerae Case in a Diarrheal Disease Outbreak in Costa Rica

This paper reports the first documented detection of *Vibrio paracholerae* in a Costa Rican foodborne outbreak, highlighting the limitations of conventional diagnostic methods and emphasizing the critical need for genomic surveillance to accurately identify emerging enteropathogens.

The Gist

The Story: A Mystery in the Kitchen

Imagine a non-profit home in Costa Rica that cares for people with severe disabilities. In late April 2025, several residents suddenly got very sick with bad stomach bugs (diarrhea). The local health detectives (from INCIENSA) were called in to figure out what happened.

They collected samples from the sick people and from the food served in the kitchen, specifically a vegetable blend. Their job was to play "detective" and find the germ responsible.

The First Suspects: The "Wrong" ID Cards

When the lab technicians first looked at the samples, they used standard tools to identify the germ:

• The PCR Test: This is like a quick ID card scanner. It told them, "This is Vibrio cholerae," but a harmless version that doesn't cause the famous cholera disease.
• The MALDI Test: This is like a fingerprint scanner. It also said, "Yep, that's Vibrio cholerae."
• The BAX System: Another machine used on the vegetable blend gave the same result.

At this point, everyone thought they had solved the case. They believed the vegetable blend contained a specific type of Vibrio cholerae.

The Plot Twist: The High-Definition Camera

But the detectives weren't 100% sure. The standard tools (the ID card and fingerprint scanners) are good, but sometimes they can't tell the difference between two very similar twins. To get the truth, they used Whole Genome Sequencing.

Think of this as taking a high-definition, 4K video of the germ's entire DNA library, rather than just looking at a blurry photo. They compared this super-detailed DNA map against a massive library of known bacteria.

The Real Culprit Revealed

The high-definition DNA analysis revealed a surprise:

• The standard tools had made a mistake. They thought the germ was Vibrio cholerae.
• The DNA analysis showed the germ was actually Vibrio paracholerae.

The Analogy: Imagine you have two brothers who look almost identical. One is named "Cholera" and the other is "Paracholera." The standard tools were like squinting from far away and saying, "That's definitely Cholera!" But the DNA analysis was like zooming in with a microscope and realizing, "Wait, that's actually Paracholera! They look alike, but they are different people."

The Smoking Gun

The DNA analysis did two more important things:

1. It confirmed the source: The germ found in the sick people and the germ found in the vegetable blend were genetically identical. They were like two photocopies of the same document. This proved the vegetable blend was indeed the source of the outbreak.
2. It drew a family tree: The scientists built a "family tree" of the bacteria. The new germ sat on a branch with other V. paracholerae bacteria, far away from the branch where V. cholerae lives. This confirmed the standard tools had misidentified the species.

The Big Lesson

This paper claims two main things:

1. First Time: This is the first time anyone has officially found Vibrio paracholerae causing a foodborne outbreak in Costa Rica.
2. The Tools Need an Upgrade: The paper warns that the standard "quick" tests (PCR, MALDI, BAX) are not sharp enough to tell the difference between these two very similar bacteria. They can get confused.

The Conclusion: To catch these tricky, emerging germs accurately, health labs need to upgrade from "squinting photos" to "high-definition DNA videos" (genomic surveillance). This ensures they know exactly what they are fighting so they can protect the public correctly.

Technical Summary

Technical Summary: Detection of a Vibrio paracholerae Case in a Diarrheal Disease Outbreak in Costa Rica

Problem and Context
In late April 2025, the Costa Rican Institute for Research and Teaching in Nutrition and Health (INCIENSA) responded to an acute diarrheal disease outbreak at a non-profit foundation in Alajuela, Costa Rica. Initial surveillance efforts identified Rotavirus A in clinical samples and, critically, detected Vibrio cholerae non-O1, non-O139 (ctxA negative) in both clinical stool samples and a vegetable blend food sample using conventional methods (BioFire FilmArray, BAX Q7 system, and MALDI-TOF). However, the taxonomic identification of these Vibrio strains proved ambiguous, as conventional PCR and MALDI-TOF methods are known to struggle with distinguishing between closely related species within the Vibrio genus.

Methodology
To resolve the taxonomic uncertainty and confirm the genomic relationship between the clinical and food isolates, the authors performed Whole Genome Sequencing (WGS).

• Sequencing: Libraries were prepared using the Illumina DNA Prep kit and sequenced on an Illumina MiSeq system (250-cycle paired-end run).
• Bioinformatics Pipeline: De novo genome assembly was conducted using Shovill within the thiaprok_illumina_pe_PHB pipeline on the Terra.Bio platform.
• Identification Tools: The study employed multiple computational tools for species identification, including Average Nucleotide Identity (ANI) via mummer, Gambit, Kmerfinder, and Ribosomal MLST (rMLST).
• Phylogenetic Analysis: A Neighbor-Joining analysis was performed to compare the query strains against a reference set of 56 core genome sequences from various Vibrio species, including a reference sequence for V. paracholerae (O75TS_SAN5442A2).

Results
The study yielded discordant results between different identification methods:

• Conventional vs. Genomic Tools: While ANI and Kmerfinder classified the strains as V. cholerae, the Gambit tool and rMLST characterized them as V. paracholerae.
• Phylogenetic Resolution: The phylogenetic analysis provided the highest resolution, demonstrating that both the clinical and food isolates clustered within a monophyletic group specific to V. paracholerae, distinct from the V. cholerae branch. The isolates were closely related to the reference V. paracholerae strain and showed zero Single Nucleotide Polymorphism (SNP) differences between the food and clinical samples, confirming a common source.
• Epidemiological Link: The analysis confirmed the vegetable blend as the source of the outbreak and established the first documented presence of V. paracholerae in a foodborne disease event in Costa Rica.

Key Contributions and Claims
The primary contribution of this work is the first documented detection of V. paracholerae in a foodborne outbreak in Costa Rica, linking clinical cases directly to a contaminated vegetable blend. The authors highlight the limitations of current standard surveillance tools (PCR, MALDI-TOF, and BAX Q7 systems) in accurately discriminating between V. cholerae and V. paracholerae.

Significance
The paper asserts that these findings underscore the necessity for national reference centers to adopt genomic surveillance tools. The authors argue that relying solely on conventional methods may lead to misidentification of emerging enteropathogens. By integrating next-generation sequencing and bioinformatics, public health systems can more accurately characterize persistent and emerging pathogens, thereby supporting more effective epidemiological surveillance and outbreak response. The study was conducted as part of routine public health surveillance under the legal mandate of INCIENSA and the Ministry of Health of Costa Rica.