1) The vendor himself. I am not referring to all vendors. Some vendor never prepare the foods in sanitary manner. Vendors with contagious disease, simple colds or Hepatitis A, can transfer the sickness to their customers.
2) The surroundings. Street foods are sold in open environment. On street sides where hundreds or thousands of passing vehicles discharge toxic fumes. Street foods are also unprotected from dirt and other foreign bodies.
3) The costumers. Yes, the customers can make street foods not safe. This is true for foods serve with sauce. Notice how the isaw, dugo and fish ball are served: The vendor will fry the fish balls. Then the customers will get them by means of bamboo sticks and dip it into sauce of choice – sweet, hot and sweet and sour.
Whats wrong with the serving method? a) The bamboo sticks are pack in a container where customers can freely get it. A contagious disease or hazardous microorganisms might transfer from the infected person to group of bamboo sticks then to next customers. b) After eating, some customers have the tendency to get another set of fish balls using the same stick or they re-dip the unfinished fish balls. Cross contamination is from mouth to fish balls or sauce. c) Talking in front of foods can also be a vessel of cross contamination through accidental spray of saliva.