E. coli O157 Outbreak in a Daycare Environment: Screening of Asymptomatic Attendees and Staff, Oregon, 2014

BACKGROUND:  During September–October 2014, three cases of E. coliO157:H7 (O157) infection were identified in a daycare in a rural Oregon community.  Implemented control measures included active case finding, testing of students/staff with diarrheal illness, education of staff, review of cleaning procedures, and exclusion of the cases until two stools tested negative. The cases occurred over a 7-week period in two separate classrooms. Previous studies recommended screening of all attendees to rule out ongoing person to person transmission among asymptomatic carriers, the school voluntarily closed and all staff and students submitted stools for testing.

METHODS:  Cases were interviewed with both a standardized case report form and a hypothesis-generating questionnaire.  High-risk foods were tested. O157 isolates were analyzed by PFGE. Cases were defined as school-associated persons with PFGE-matching O157 and illness onset during 9/1/14 – 11/12/14. Attendance records were reviewed for unreported cases. Parents were asked to report gastrointestinal illnesses by letters (10/10/14, 10/26/14) and during public health facilitated meetings (10/12/14, 10/28/14).  Staff reported any gastrointestinal illness in children or staff.  Symptomatic persons were tested.  Multiple environmental assessments and testing occurred, including drinking water testing.  In early November, all children and staff submitted fecal specimens for O157.

RESULTS:  Environmental inspections identified no concerns in the operations of the school or in the food vendor. Active surveillance resulted in ten children and two staff being tested, all were negative O157. Case #2 consumed UV-treated, unpasteurized cider from a local farm and ground beef that was noncommercially butchered; both tested negative for O157. Drinking water samples were without coliforms or E. coli. All (79) staff and students submitted fecal specimens; none yielded.  One environmental sample from an outdoor dirtpit play area was a PFGE match to the cases.

CONCLUSIONS:  Three cases of O157 infection occurred in a daycare setting over 7 weeks; interviews did not identify any direct contact among cases.  Active surveillance and stool testing of symptomatic children did not identify additional cases. Finally, screening of all staff and students did not identify additional cases of E. coli O157.  Other studies suggest that screening based on reported symptoms only may be insufficient to identify cases that might be contributing to ongoing transmission. However, we found that screening in this setting is resource-intensive and not uniformly fruitful. A decision to screen needs to be weighed against the likelihood of identifying asymptomatic carriers who are likely to transmit infection to others.