Objective:

To quantify the intersection of acute rubella and parvovirus B19 infections with rheumatoid arthritis suspicion and identify misclassification risks, emphasizing the clinical significance of these findings.

Approach:

Key Findings:

• 2.1% of adults tested positive for rubella IgM; these patients had higher rates of arthritis-related ICD-10 codes and same-day RA biomarker testing, but no significant association with subsequent RA diagnosis.
• Rubella IgM-positive adults showed higher biomarker positivity rates (26.4% vs 11.1%) but no statistically significant association with subsequent RA diagnosis.
• 2.1% of adults tested positive for B19V IgM; these patients had significantly higher rates of arthritis-related diagnostic codes.
• B19V IgM positivity was associated with a 33% increased risk of future suspected RA diagnosis, likely reflecting persistent joint symptoms rather than progression to RA.

Interpretation:

Acute rubella can prompt RA evaluation but does not predict RA development, while parvovirus B19 may mimic RA without leading to joint erosion typical of RA, highlighting the importance of accurate diagnosis.

Limitations:

• The study relies on serologic evidence and diagnostic coding, which may not capture all cases accurately and could introduce biases.
• B19V viraemia typically resolves before arthritis onset, complicating diagnosis.

Conclusion:

Differentiating between B19V arthritis and RA is challenging, emphasizing the need for timely identification of B19V IgM during acute illness to avoid misclassification.

Sources:

• BMJ Open
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