Title: Use of Syndromic Surveillance in the investigation of Salmonella Wandsworth Outbreak
1Use of Syndromic Surveillance in the
investigation ofSalmonella Wandsworth Outbreak
- Erin L. Murray, MSPH
- New York City Department of Health and Mental
Hygiene
2Overview
- Syndromic surveillance in NYC
- Multi-state S. Wandsworth outbreak
- Diarrhea activity in NYC, late June 2007
- Epidemiologic investigation
3NYC Syndromic Surveillance Systems
- Emergency Department (ED)
- 46/61 EDs
- 90 of ED visits
- 8500 visits/day
- Analyzed and monitored 7 days/week
- Over-the-counter (OTC) sales
- 27,500 units sold/day
- Analyzed 7 days/week
4NYC Experience Investigating Syndromic
Surveillance Signals
- Infrequently indicate an outbreak
- Only 2 investigated spatial signal linked to real
outbreak - Investigations are resource intensive
- Rarely conduct large scale investigations
5Multi-state S. Wandsworth Outbreak
- May 16 CDC announced
- 23 states involved
- 70 cases
- Onsets February 26 July 4, 2007
- 77 reported bloody diarrhea
- 92 3 years of age
- Linked to Veggie Booty snack food
- FDA recall on June 28
6Diarrhea Activity
Notification of multi-state S. Wandsworth outbreak
CDC
ED
Results assessed
OTC
21 T
25 M
26 T
20 W
27 W
28 T
23 S
22 F
24 S
June 2007
7Diarrhea Trends June 20-26
- 1 area with higher proportion of ED visits for
diarrhea than others - 3 of 6 hospitals had larger increases than other
hospitals
8Diarrhea Activity
FDA
Veggie Booty recall
Health Alert on S. Wandsworth
outbreak
NYCDOHMH
Notification of multi-state S. Wandsworth outbreak
CDC
ED
OTC
21 T
25 M
26 T
20 W
27 W
28 T
23 S
22 F
24 S
June 2007
9Objective
- Determine if increases in diarrheal illness
detected through syndromic surveillance in June
2007 were associated with a multi-state outbreak
of S. Wandsworth
10Investigation Methods
- Case-control study initiated July 3 among lt5 year
olds - Cases
- Children who visited ED for diarrhea at 3
hospitals with noted increases in diarrheal
illness from June 20-26 - Controls
- Children who visited ED for Other conditions at
same hospitals from June 20-26 - Other Chief complaints that did not mention
respiratory, GI, asthma, or severe illness
symptoms
11Investigation Methods
- Patient contact information obtained from
hospitals - Questionnaire administered to parent or guardian
of cases and controls - History of condition resulting in ED visit
- Included diarrhea and stool culture questions
- Food exposures
- Veggie Booty
- Other exposures
- Ill family members
12Investigation Analysis
- Two case/control designations
- ED chief complaint of diarrhea
- Interview report of diarrhea
- Odds ratios calculated
- 0.5 correction in every cell if zero-cell present
- 95 confidence intervals calculated
13Results
- 51 of 39 cases in diarrhea syndrome completed
interviews (n20) - 43 of 89 controls completed interviews (n38)
- Overall response 45
14Case/Control Designations
Interview
Chief Complaint
1 childs diarrhea symptom information was
missing on interview
15Results by Case/Control Status
- Chief complaint (diarrhea syndrome)
- OR 1.7
- 95 CI (0.1, 29.4)
4 controls had missing Veggie Booty consumption
information
16Results by Case/Control Status
- Interview (reported diarrhea)
- OR 8.3
- 95 CI (0.4, 182.7)
4 controls had missing Veggie Booty consumption
information 1 childs diarrhea symptom
information was missing on interview
17Laboratory Findings
- 7 of 20 cases reported providing stool cultures
in ED - None were children who ate Veggie Booty
- Only confirmed 2 had cultures taken
- 1 negative
- 1 positive for Campylobacter
18Limitations
- Delay from signals to interviews - Recall bias
- 11 days from OTC signal day to request for
contact information from EDs - 6 additional days to obtain all patient contact
information - Small sample size - Limited power
- Could not differentiate excess diarrhea from
baseline diarrhea - Bias towards null
19Retrospective Assessment
- Could an integration of other data sources have
prompted an earlier detection and response to
this outbreak? - Why didnt we detect an association between
Veggie Booty and diarrhea ED visits?
20S. Wandsworth in NYC
- 8 NYC residents culture confirmed
- Onset dates March 4 May 19, 2007
- All lt5 years of age
- Residents of 3 NYC counties
21Bronx
Hospital3/4/2007
Queens
Manhattan
Zip Code 3/14/2007
Brooklyn
22Zip Code 4/15/2007
Bronx
Queens
Manhattan
Brooklyn
23Retrospective Assessment
- Could an integration of other data sources have
prompted an earlier detection and response to
this outbreak? - Why didnt we detect an association between
Veggie Booty and diarrhea ED visits?
24Estimated Total Number of Cases in NYC
- FoodNet (CDC)
- 39 cases of Salmonella for each culture confirmed
case - Expected cases in NYC ?
- 8 x 39 312
- 4 per day (March 4 May 19)
25Expected Number of ED Visits
- FoodNet
- 12 of people with acute gastrointestinal illness
seek care (all ages) - Assumptions
- May be higher among young children
- Higher among those with bloody diarrhea
- Most would seek care from primary care provider
- 25 of NYC cases visited ED
- Of ED visits, some would not be identified by
diarrhea syndrome
26Expected Number of ED Visits
- S. Wandsworth outbreak ? very few (1/day)
additional ED diarrhea visits - Limited analysis 7 day period (6/20-26)
- Limited analysis to 3 (of 61) EDs
27Conclusions
- Outbreak unlikely to be captured by syndromic
surveillance - Small size
- Misalignment of syndromic signals and cases
- Spatially
- Temporally
- Delay in laboratory reporting
28Recommendations
- Create better methods for visualizing syndromic
surveillance data on daily basis - Integrate data from multiple systems
- Improve geographic visualization
- Incorporate laboratory data
- Increase the number of laboratories reporting
electronically
29Recommendations
- Develop rapid methods for obtaining patient
information - Identify appropriate contact person for data
extractions during an emergency - Identify methods on both sides that will ease
burden of data extraction - Create secure transfer methods for patient records
30Acknowledgements
- Richard Heffernan
- Lara Kidoguchi
- Bernadette Fascina
- Don Olson
- Debjani Das
- Andrea Fischer
- Giselle Merizalde
- Glenette Houston
- Staff from hospitals involved in investigation
- Alice Yeung
- Don Weiss
- Alejandro Cajigal
- Martha Felder
- Timothy Clark
- Kristin Wall
- Chris Goranson
- Trang Nguyen
- University of Pittsburgh (RODS)
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34Expected Number of ED Visits
- S. Wandsworth outbreak ? very few (1/day)
additional ED diarrhea visits - Limited analysis 7 day period (6/20-26)
- Expected 7 cases in EDs citywide
- Limited analysis to 3 (of 61) EDs
- Expect .1 cases/hospital ? .3 cases total
- Observed 2 possible cases
35Limitations
- S. wandsworth outbreak began in late-February
- Compared proportion of diarrhea visits in late
June to those in early/mid-June - Comparison baseline contained Salmonella outbreak
36Findings
- 8-fold increase in odds of eating Veggie Booty
among children with diarrhea - Not significant very large confidence interval
- No laboratory confirmation of Salmonella
- Chief complaint doesnt capture all symptoms
37Findings
- Exposed difficulties in obtaining high volume of
patient contact information from hospitals - Identifying correct person to handle request
- Ability to create electronic database of specific
records - Security of transferring files to NYCDOHMH
38NYC Syndromic Surveillance Systems
- Emergency department visits
- Pharmacy Sales
- RODS
- Over-the-counter (OTC)
- NYC specific system
- OTC
- Prescription
- EMS calls
- Hospital outpatient visits
- School nurse clinic visits
39Investigation Analysis
- Two case/control designations
- ED chief complaint of diarrhea
- Interview report of diarrhea
- Odds ratios calculated
- 0.5 correction in every cell if zero-cell present
- 95 confidence intervals calculated
40Case/Control Designations
41NYC Experience Investigating Syndromic
Surveillance Signals
- 375 statistically significant spatial signals
from 2002-2005 - 75 investigated
- 13 (of 117) for diarrhea syndrome
- 1 diarrhea signal determined to be true outbreak
- Signal investigations are resource intensive and
infrequently indicate an outbreak - Rarely conduct large scale investigation