Fulminant psittacosis requiring mechanical ventilation and demonstrating serological cross-reactivity between Legionella longbeachae and Chlamydia psittaci.

Chlamydia psittaci infection typically causes a mild respiratory illness in humans. Severe respiratory failure requiring mechanical ventilation or intensive care therapy is an uncommon development. The aetiological agents causing severe community acquired pneumonia often remain undetermined. Serological tests may aid in diagnosis. We present two cases of fulminant psittacosis, one demonstrating early cross-reactivity with Legionella longbeachae.