A 55-year-old poultry worker develops severe pneumonia with lymphopenia and very high ferritin. Rapid influenza test is negative. Nasopharyngeal swab RT-PCR detects H5 haemagglutinin. Which statement about this virus is most accurate?

• A H5N1 efficiently transmits human-to-human by droplets
• B Oseltamivir is ineffective due to N1 neuraminidase resistance in all H5N1 strains
• C Standard influenza A/B RIDT is as sensitive as RT-PCR for H5N1 detection
• D H5N1 HA binds α-2,3 sialic acid receptors predominant in lower respiratory tract, explaining severe pneumonia ✓

Explanation

H5N1 haemagglutinin preferentially binds α-2,3-linked sialic acid receptors, which predominate on type II pneumocytes and bronchiolar epithelium in the deep lower respiratory tract, explaining severe pneumonia with high mortality; in contrast, seasonal influenza binds α-2,6 sialic acid in upper airways. H5N1 does not transmit efficiently between humans. Most H5N1 strains remain sensitive to oseltamivir, though higher doses are recommended. Standard RIDT has poor sensitivity (<40%) for H5N1.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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