ABxSure for differentiating bacterial from viral Infection

The paper introduces ABxSure, a deployable diagnostic device that utilizes CD64, CD169, and total leukocyte count biomarkers to accurately differentiate between bacterial and viral infections, thereby addressing the clinical challenge of symptom overlap and reducing the overprescription of antibiotics.

The Gist

Imagine you have a fever, a cough, and feel terrible. You go to the doctor, but here's the problem: bacteria and viruses often throw the exact same "party" in your body, making you feel sick in identical ways.

Because the symptoms look the same, doctors often play it safe. They prescribe antibiotics just in case it's bacteria, even if it's actually a virus. This is like calling a plumber to fix a leaky faucet when the problem is actually a broken lightbulb. It doesn't help, and worse, it teaches the "bad guys" (bacteria) how to become immune to the medicine, leading to superbugs that are hard to kill.

Enter "ABxSure": The Detective for Your Blood.

The researchers in this paper built a new, tiny machine called ABxSure to solve this mystery. Think of it as a smart, automated blood detective that can tell the difference between a bacterial invader and a viral one in just 20 minutes.

Here is how it works, using some simple analogies:

1. The "ID Cards" (The Biomarkers)

Your white blood cells (the body's security guards) wear different "ID cards" depending on who they are fighting.

• The Bacterial Badge (CD64): When bacteria attack, your neutrophils (a type of guard) put on a giant, glowing "Bacterial Alert" badge. The more bacteria, the bigger and brighter the badge.
• The Viral Badge (CD169): When viruses attack, your monocytes (another type of guard) put on a different, specific "Viral Alert" badge.
• The Crowd Count (Total WBC): The machine also counts how many guards are on duty in total.

2. The "Magic Cartridge" (The Lab in a Box)

Usually, checking these badges requires a massive, expensive machine in a big hospital lab (like a Flow Cytometer) that takes hours and costs a lot of money. It's like needing a full forensic team to check a single fingerprint.

ABxSure is different. It uses a microfluidic cartridge (a tiny plastic chip with microscopic channels).

• The Process: You put a tiny drop of blood (like a finger prick) into the cartridge.
• The Cleanup: Inside, a special fluid acts like a "red blood cell eraser," dissolving the red cells so the white blood cells (the guards) stand out clearly.
• The Tagging: The machine automatically mixes the blood with special glowing dyes. These dyes are like high-lighter pens that stick only to the specific ID badges (CD64 or CD169).
• The Filter: The blood flows through a tiny sieve (a membrane) that catches the guards while letting the liquid wash away.

3. The "Flashlight Reader" (The Device)

Once the guards are caught on the sieve, the ABxSure device shines a specific light on them.

• If the guards are glowing bright red, it means they have the Bacterial Badge.
• If they have the Viral Badge, they glow differently.
• The device counts the glow and tells the doctor: "This is a bacterial infection" or "This is a viral infection."

Why is this a Big Deal?

• Speed: It takes about 20 minutes from the finger prick to the answer. Traditional lab tests can take 24 to 48 hours.
• Simplicity: It's automated. You don't need a PhD to run it; a nurse or even a clinic worker can do it.
• Cost: It's designed to be cheap and portable, unlike the giant, expensive machines currently used.
• The Result: If the test says "Virus," the doctor knows not to give antibiotics. If it says "Bacteria," they know to start treatment immediately.

The Bottom Line

The researchers tested this new "detective" against the expensive, gold-standard hospital machines. The results were nearly identical (about 89% correlation).

ABxSure is like upgrading from a slow, expensive, manual typewriter to a fast, affordable smartphone. It helps doctors make the right call quickly, stops the overuse of antibiotics, and helps us fight the growing threat of superbugs. It turns a complex, days-long mystery into a quick, clear answer right at the patient's bedside.

Technical Summary

1. Problem Statement

• Diagnostic Gap: Bacterial and viral infections present with overlapping symptoms (fever, fatigue, cough), making clinical differentiation difficult based on visible signs alone.
• Consequences: This ambiguity leads to the empirical overprescription of antibiotics for viral infections to avoid missing severe bacterial cases (e.g., sepsis). This misuse is a primary driver of Antimicrobial Resistance (AMR), projected to cause 10 million deaths annually by 2050.
• Limitations of Current Diagnostics:
  • Standard Blood Tests: Markers like WBC count, neutrophils, and CRP lack specificity for distinguishing infection types.
  • Microbiological/Nucleic Acid Tests: Blood cultures take 24–48 hours, and PCR requires specific pathogen detection which can be delayed or impossible if the pathogen is inaccessible (e.g., pneumonia).
  • Gold Standard (Flow Cytometry): While flow cytometry can quantify specific immune biomarkers (CD64 and CD169), it is expensive (~$30/test), time-consuming, requires centralized labs, and needs trained personnel, limiting its utility in Point-of-Care (PoC) settings.

2. Methodology and System Design

The authors developed ABxSure, a deployable, automated PoC diagnostic system designed to quantify specific host immune biomarkers to differentiate infection types.

A. Biological Markers

The system targets three key indicators:

1. CD64 (FcγRI): Expressed on neutrophils. Its expression increases 8–10 fold within 4–6 hours of bacterial infection due to stimulation by IFN-γ and G-CSF. It serves as a specific marker for bacterial infection.
2. CD169 (SIGLEC-1): Expressed on monocytes. Its expression increases exponentially in response to Type I Interferons (IFN-α) during viral infections.
3. Total Leukocyte Count (WBC): A general health indicator.

B. Device Architecture

ABxSure integrates a microfluidic cartridge with an automated optical detection device.

• Microfluidic Cartridge:
  • Fabrication: 3D printed using stereolithography (SLA) with polypropylene assembly and polycarbonate (PC) covers.
  • Components: Includes a sample chamber (pre-loaded with RBC lysis buffer), wash chamber, three sample wells, mixing loops (252mm serpentine channels), and polycarbonate track-etched membranes (3μm pore size) for cell capture.
  • Workflow:
    1. Lysis: Whole blood is lysed to remove RBCs and reduce viscosity.
    2. Splitting: The lysate is split into three wells (100 μL each).
    3. Labeling: Cells are mixed with fluorophore-conjugated antibodies (anti-CD64-PE, anti-CD169-PE) and a nucleic acid dye (Syto85 for total WBC) via back-and-forth peristaltic pumping for 15 minutes.
    4. Capture & Wash: Cells are captured on the membranes; unbound reagents are washed away.
    5. Readout: The optical reader quantifies fluorescence on the membranes.
• Hardware & Electronics:
  • Optical Module: Uses a 565nm LED (Green Light) for excitation and a 633nm emission filter to detect Phycoerythrin (PE) and Syto85 fluorescence.
  • Control: A microcontroller manages pneumatics (positive/negative pressure) for fluid handling, a touchscreen GUI for user interaction, and an ADC for signal conversion to Relative Fluorescence Units (RFU).

C. Validation Strategy

The system was validated against two commercial standards:

1. Multimode Plate Reader: For fluorescence intensity comparison.
2. Flow Cytometer (BD Fortessa X20): Using PE quantification beads to calculate antibodies bound per cell (Gold Standard).

• Samples: Clinical leftover whole blood samples from IIT Delhi hospital and in-vitro differentiated HL60 cell lines (simulating neutrophils and monocytes).

3. Key Contributions

• Novel PoC Device: Development of a fully automated, cartridge-based device that eliminates manual steps, making it accessible to non-experts.
• Multiplexing: Simultaneous quantification of three distinct biomarkers (CD64, CD169, and Total WBC) from a single finger-prick or small blood sample in one run.
• Cost-Effective & Rapid: Reduces turnaround time to ~20 minutes and aims to lower costs significantly compared to flow cytometry.
• Biomarker Strategy: Demonstrates that total CD64 expression on WBCs (driven largely by neutrophil upregulation) is a robust linear indicator of bacterial infection, even without sorting specific cell populations.

4. Results

• Biomarker Responsiveness: In-vitro models confirmed that IFN-γ stimulation significantly upregulates CD64, while IFN-α upregulates CD169.
• WBC Quantification:
  • ABxSure showed a strong correlation ($r = 0.93$) with hospital CBC reports for total WBC counts.
  • Bland-Altman analysis showed a mean bias of -266 cells/mL with 95% limits of agreement within acceptable ranges.
• CD64 and CD169 Quantification:
  • vs. Plate Reader: Correlation coefficients were 0.899 for CD64 and 0.89 for CD169.
  • vs. Flow Cytometer: Correlation coefficients were 0.85 for CD64 and 0.89 for CD169.
  • Agreement: Log-ratio Bland-Altman analysis indicated that after calibration, systematic bias was eliminated. CD169 showed particularly tight agreement (0.86–1.16 fold difference) compared to the plate reader.
• Cellular Insights: Analysis revealed that while neutrophils are fewer in number than monocytes in some contexts, the massive upregulation of CD64 on neutrophils during bacterial infection makes total CD64 a highly sensitive marker.

5. Significance and Impact

• Clinical Utility: ABxSure provides clinicians with rapid, objective data to distinguish bacterial from viral infections, directly addressing the root cause of antibiotic overprescription.
• AMR Mitigation: By enabling precise diagnosis at the point of care, the device supports "right-sizing" antibiotic therapy, thereby slowing the development of antimicrobial resistance.
• Accessibility: The device is designed to be compact, inexpensive, and easy to operate, bridging the gap between high-end centralized diagnostics and resource-limited settings.
• Future Potential: The platform is adaptable; reagents and membrane pore sizes can be modified for other biomarkers, making it a versatile tool for future infectious disease surveillance.

Conclusion: The paper successfully demonstrates that ABxSure is a viable, high-performance alternative to flow cytometry for quantifying immune biomarkers, offering a rapid, cost-effective solution to the critical global challenge of differentiating bacterial and viral infections.