Someone comes in to the hospital with an infection. The infection does not respond to antibiotics, and the organism is too small to see when viewed under the microscope, even smaller than a bacterium....

Someone comes in to the hospital with an infection. The infection does not respond to antibiotics, and the organism is too small to see when viewed under the microscope, even smaller than a bacterium. What is the most likely cause of the illness? Bacteria Virus Fungus Protozoan