What is the infectious dose of Legionella causing food infections?
Legionella does not cause food infections.
What kind of disease does Legionella cause then?
Legionella causes pneumonia, a lung infection. Diarrhea can be a common symptom because the transmission is from contaminated water. However, the mode of transmission is aspiration, not aerosolisation as is commonly believed.
So if a person drinks water with Legionella, what is the infectious dose that will make them sick?
The infectious dose for contracting pneumonia is unknown, but it will be much lower than the infectious dose for typical food borne infections since the Legionella is aspirated directly into the lung.