A 12-year-old boy living in a dengue-endemic Indian city presents with fever on day 3. Dengue IgM is negative but dengue IgG is strongly positive and rising rapidly. Which pattern of infection does this indicate?

• A Secondary dengue infection ✓
• B Primary dengue infection
• C Recent yellow fever vaccination
• D Chikungunya cross-reactivity

Explanation

In secondary dengue, pre-existing cross-reactive IgG from a previous infection rises rapidly and reaches high titres within the first few days, while IgM appears late and may remain low. Primary infection shows the opposite pattern, with IgM rising from day 5 and IgG appearing slowly. Chikungunya does not produce strongly positive dengue-specific IgG, and yellow fever vaccination is not administered in India's routine programme.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.