Multistate E. coli O121 Cluster Associated with Raw Clover Sprout Consumption

BACKGROUND:   Between May 5 and May 13, 2014 6 cases of shiga-toxin-2 producing E. coli (STEC) were reported regionally to either the Spokane Regional Health District (SRHD) in Washington State or just across the border to the Panhandle Health District in Northern Idaho. PulseNet data were reviewed and a multistate investigation was conducted to determine the extent of the outbreak and most likely source of infection.

METHODS:   Cases were classified as outbreak-associated if illness onset was during April 15-June 25, 2014 and the E. coli O121 strain detected was 1405WAEXK-1. Review of food histories implicated raw clover sprouts from Idaho sprout Producer A. FDA conducted a product trace-forward, seed trace-back, and inspection of Producer A facilities. Sprout samples from Producer A were collected from food establishments and tested. Producer A did not issue a voluntary product recall; product was removed from shelves at public health agencies’ suggestion. Idaho, Montana, and Washington public health agencies disseminated Health Alert messages and CDC and FDA issued media alerts.

RESULTS:   19 outbreak-associated cases were identified from 6 states: CA(1), ID(3), MI(1), MT(2), UT(1), and WA(11). Illness onset dates ranged from May 1 to May 20; the median age was 27y (range: 11y to 52 y); 13 (68%) were female, 7 (44%) were hospitalized, and no hemolytic uremic syndrome or deaths were reported.  Food histories were available from 16/19 cases; 13/16 (81%) reported consumption of Producer A raw clover sprouts in the week prior to illness onset.  All sprout samples from food establishments and environmental samples collected by FDA were negative for E. coli O121; however, FDA noted 9 violations in Good Manufacturing Practice (GMP) during their inspection. Implicated seed lots were removed from production and sprouting and packaging by Producer A were halted until violations were addressed to FDA’s satisfaction. Seed source information was not made available.

CONCLUSIONS:  A temporal multistate cluster of E. coli O121 cases, corroborated by PulseNet, occurred in May, 2014. Raw clover sprout consumption was a significant risk factor (p<0.00000001) for infection when compared with the 2007 FoodNet estimated consumption rate of 8%.  Because contamination of seeds and sprouts can occur at any point along the farm to table continuum, addressing violations and reinforcing GMP at the sprouter level is only part of food safety; a lack of information regarding the seed source limited opportunities for public health interventions targeted to seed management.