What is the primary common source of Giardia intestinalis infection in travelers and campers?

• A. Drinking untreated surface water (e.g., streams or lakes) without filtration or disinfection.
• B. Only direct contact with infected pets and never from water sources.
• C. Eating commercially canned foods while camping that have been properly heated before consumption.
• D. Consuming pasteurized dairy products and thoroughly cooked meats in the field.

Answer: (A)