Salmonella Surveillance Following the Introduction of a Statewide Web-Based Disease Reporting System - Iowa, 2009-2011

BACKGROUND:  Foodborne illness caused by Salmonella is of concern not only to public health because of food safety, but also to the public, as indicated by over 4,000 hits annually to the Iowa Department of Public Health’s (IDPH) Salmonella website. In 2008 the Iowa Disease Surveillance System (IDSS) was implemented, which links IDPH with local public health departments, hospitals, and laboratories via the internet.  During 2009-2011, 1,388 cases of Salmonella were reported, including 13 outbreaks and 19 PFGE clusters.  Positive Salmonella isolates are sent to Iowa’s State Hygienic Laboratory (SHL) for serotyping and pulsed-field gel electrophoresis (PFGE).  All reported cases are investigated for risk factors.

METHODS:  The system was evaluated using CDC’s “Updated Guidelines for Evaluating Public Health Surveillance Systems.”  Sensitivity was calculated by comparing Iowans reported with Salmonella in hospital discharge data with those reported to IDSS.  Data completeness was measured by comparing reported cases to Salmonella isolates sent to SHL for confirmation and genetic testing.  Timeliness was calculated by measuring the time required for each step of the case investigation.  Ease of entry and access to data was evaluated by interviewing IDSS users.  Accuracy of reporting Salmonella deaths was assessed by comparing death certificate information with case investigation results.

RESULTS:  Of 203 hospitalized cases in the hospital discharge data, 183 were also reported to IDSS (90% sensitivity). Analyses of data completeness demonstrated that SHL received isolates for 94% (1,057/1,114) of all culture confirmed Salmonella cases.  Average time from initial diagnosis to completion of the case interview was 13.9 days.  Of five IDSS users interviewed, all found it easy to enter data into IDSS, and four felt it was easy to access data in IDSS.  Four deaths due to Salmonella were reported in IDSS, all with detailed supporting information.  However, only one death certificate mentioned Salmonella as a cause of death.

CONCLUSIONS:  Identifying the hospitals least likely to report would allow IDPH to target education and potentially increase reporting of hospitalized cases.  Outbreaks are more easily identified because of the high percentage of isolates sent to SHL, but outbreak investigations are hindered by poor risk factor recall due to the lag time from initial diagnosis to case interview.  Investigators should work to contact cases more quickly and enter exposure and risk factor information into IDSS quickly.  IDSS data is more accurate than death certificate data concerning Salmonella deaths and should be used for any future analyses and publications.