PROSPECTIVE INVESTIGATION OF CRYPTIC OUTBREAKS OF SALMONELLA-AGONA SALMONELLOSIS

The number of Salmonella agona isolates reported annually in Texas fro m 1992 through 1994 ranged from 14 to 21. An increase in incidence of S. agona infections was noted in the fall of 1995, Pulsed-field gel el ectrophoresis (PFGE) analysis identified prospectively two possible cr yptic outbreaks caused by an indistinguishable strain which was isolat ed from 18 of 59 patients who were culture positive from March through December 1995. These 18 patients had onset of illness from 20 May thr ough 3 October 1995, Eight individuals resided in the Austin area, eig ht resided in San Antonio, and two resided in Houston; none had attend ed a common social gathering or owned common pets, Six patients in San Antonio and one patient from Houston recalled eating food items from the same Mexican food restaurant in San antonio, S. agona organisms wi th the same PFGE profile were isolated from machacado, an air-dried, r aw beef product prepared at the restaurant, The machacado had been shr edded in a kitchen blender which was the probable source for cross-con tamination of other food items. Five patients in Austin reported eatin g at a popular Mexican food restaurant in Austin. Improperly prepared machacado also may have been served at the Austin restaurant; however, sufficient quantities of machacado were not available for analysis. P FGE was essential in determining whether the cases constituted outbrea ks and was invaluable in guiding the epidemiological investigation.