In terms of routes of exposure, which of the following is not a described route for Chlamydia psittaci infection in humans?

• A. Inhalation of aerosols
• B. Direct contact (beak to mouth)
• C. Ingestion of contaminated water
• D. Exposure to plumage

Answer: (C)

Chlamydia psittaci infection in humans is mainly acquired through inhalation of aerosols or dust containing the organism from infected birds, including dried bird droppings, secretions, or feather dust. Direct contact with infected birds or contaminated materials can also bring organisms to mucous membranes, making exposure through handling beak-to-mouth or contact with contaminated surfaces a possible route. Exposure to plumage fits because feather dust can contain the bacteria and be inhaled or transferred to the eyes or mouth. Ingestion of contaminated water, however, is not a described route for transmission; the primary vehicle is inhalation of aerosols, not swallowing bacteria, so waterborne transmission is not recognized as a common or described pathway for psittacosis in humans.