Anatomy of an Outbreak Kirk Smith, DVM, MS, PhD Supervisor, Foodborne, Vectorborne, and Zoonotic Diseases Unit Acute Disease Investigation and Control Section Minnesota Department of Health Office phone:

Some Recent Notable Multi-state Foodborne Outbreaks of Salmonellosis Pot pies 401 cases 42 states PCA peanut butter 691 cases 46 states Cake Mix 25 cases 9 states Tomatoes 183 cases 21 states Hot peppers 1,442 cases 44 states Veggie Booty 70 cases 23 states Peter Pan peanut butter 714 cases 48 states

Diseases Reportable to the Minnesota Department of Health Botulism (Clostridium botulinum) Campylobacteriosis (Campylobacter sp.)* Cholera (Vibrio cholerae)* Cryptosporidiosis (Cryptosporidium sp.) Enteric Escherichia coli infection (E. coli O157:H7 and other pathogenic E. coli from gastrointestinal infections)* Giardiasis (Giardia lamblia) Hemolytic uremic syndrome Listeriosis (Listeria monocytogenes)* Salmonellosis, including typhoid (Salmonella sp.)* Shigellosis (Shigella sp.)* Toxoplasmosis Yersiniosis (Yersinia sp.)* FOODBORNE AND WATERBORNE DISEASES * Submit isolates or clinical materials to the Minnesota Department of Health

Submission of isolate to public health lab Report of case to public health Becomes ill Confirmation/ serotyping, PFGE subtyping Interview Lab and epi data combined Person eats contaminated food Stool sample positive Goes to doctor, stool sample collected days days (incubation) days1 - 5 days days

Reportable Bacterial Enteric Pathogen Surveillance in Minnesota Isolates must be submitted to the Minnesota Department of Health Real-time pulsed-field gel electrophoresis (PFGE) subtyping of all isolates Routine, real-time interviews of all cases

Molten agarose Pulsed-Field Gel Electrophoresis (PFGE) Lysis Enzyme digestion (XbaI) Bacteria Pulse electrophoresis DNA 18 hours 1.5 hours

The National Molecular Subtyping Network for Foodborne Disease Surveillance Area Labs National Database FoodNet Sites FDA, USDA Lab

PulseNet Laboratory Network Local Databases PulseNet National Databases (CDC) Participating Labs PFGE Patterns

Bacterial Isolate Flow from Clinical Labs to Public Health Labs Completeness and timeliness of isolate submission to public health labs, and timeliness of serotyping/PFGE subtyping at public health labs, determines the sensitivity of outbreak detection –i.e., need this for optimal detection of outbreaks (local and multistate) caused by Salmonella, E. coli O157:H7

Minnesota Surveillance Philosophy Interview all cases, ASAP Collect details on specific exposures –Restaurant, grocery store names –Brand names –Open-ended food histories Investigation of all PFGE clusters –Intensity/resource expenditure depends on the exact nature of the cluster –Follow leads aggressively

Standard Questionnaire for Salmonella, E. coli O157 cases

Minnesota Surveillance Philosophy Interview all cases, ASAP Collect details on specific exposures –Restaurant, grocery store names –Brand names –Open-ended food histories Investigation of all PFGE clusters –Intensity/resource expenditure depends on the exact nature of the cluster –Follow leads aggressively

Response for PFGE Clusters Minimum: Compare case interviews Maximum: Case-control study Food Testing: Before, during, or after case control study “Informational” product tracing

Minnesota Approach to Investigation of PFGE Clusters: Dynamic Cluster Investigation Model Case #1Case #2Case #3Case #4

Dynamic Cluster Investigation - Pot Pies Consumed Banquet PP 4 10/4 afternoon “trawling” questionaire 1 Initial trawling questionnaire interview date 9/10 2 9/ /3 night Re-interviewed cases about frozen foods and pot pies 10/4 morning 10/4 evening PP Exposure added

Team Diarrhea Fall 2007

Epidemiologic Follow-up of Cases Determines the likelihood of identifying the source of an outbreak

Epidemiologic Data are Dirty Not all exposed people get sick Some people get sick without being exposed Not all “exposed people” are really exposed Not all “unexposed people” are really unexposed Not all sick people are really sick

Presentations of Outbreaks due to Commercially Distributed Food Items Cases in community, no obvious common exposure –Retail food (grocery stores) Cases occur among patrons of restaurant(s) Cases clustered in institution(s) Any combination of above three

Presentations of Outbreaks due to Commercially Distributed Food Items Cases in community, no obvious common exposure –Retail food (grocery stores) Cases occur among patrons of restaurant(s) Cases clustered in institution(s) Any combination of above three

Dole Prepackaged Salad O157 Outbreak September 27, 2005 Three O157 isolates with indistinguishable PFGE patterns identified by Minnesota Public Health Laboratory PFGE pattern new in Minnesota, rare in United States –0.35% of patterns in National Database

Outbreak Investigation - Methods September 28–29, 2005 Additional O157 isolates received and subtyped by PFGE –7 isolates demonstrated outbreak PFGE subtype Supplemental interview form created Case-control study initiated –Age-matched community controls recruited through sequential digit dialing anchored on case’s telephone number

Case-Control Study Results Exposure Cases Controlsp-valueMatched OR*95% CI † Any lettuce9/1017/ –25.0 * OR = odds ratio † CI = confidence interval 9/10 Prepackaged lettuce salad 10/ –59.6 Brand A prepackaged lettuce salad 9/105/ –67.3

E. coli O157:H7 Cases Associated with Brand A Prepackaged Lettuce by Date of lllness Onset Date of Onset Number of Cases September October Initial cluster of 3 isolates among MN residents identified. Case-control study initiated. Case-control study implicated Brand A salad.

E. coli O157:H7 Cases Associated with Brand A Prepackaged Lettuce by Date of lllness Onset Date of Onset Number of Cases September October Initial cluster of 3 isolates among MN residents identified. Case-control study initiated. Case-control study implicated Brand A salad.

E. coli O157:H7 Cases Associated with Brand A Prepackaged Lettuce (n=26) Date of Onset Number of Cases September October WI Minnesota Additional states OR

Presentations of Outbreaks due to Commercially Distributed Food Items Cases in community, no obvious common exposure –Retail food (grocery stores) Cases occur among patrons of restaurant(s) Cases clustered in institution(s) Any combination of above three

Salmonella Saintpaul Patron Cases Associated with Restaurant A by Date of Isolate Receipt in MDH Laboratory, June 2008 June Date of Isolate Receipt Number of Cases Two cases name Restaurant A

Restaurant A Outbreak June 30, 2008 MDH and Ramsey County staff visited restaurant –Interviewed management and employees –Collected invoices for ingredients used in dishes consumed by cases –Requested credit card receipts from same time period –Obtained copies of menu

Salmonella Saintpaul Patron Cases Associated with Restaurant A by Date of Isolate Receipt in MDH Laboratory, June 2008 June Date of Isolate Receipt Number of Cases Second case names Restaurant A Visit restaurant Initial case-control study/traceback results to CDC

Univariate and Multivariate Results of Minnesota Case-Control study Ingredient No. cases exposed/total ORpaOR p Red salsa13/1814.7<0.001Not significant Avocado salsa14/197.5<0.001Not significant Mexican garnish 17/1969<0.001Not significant Red peppers17/1943<0.001Not significant Cilantro18/1921.4<0.001Not significant Fresh tomatoes 6/ Not significant Jalapenos17/1969< <0.001

Presentations of Outbreaks due to Commercially Distributed Food Items Cases in community, no obvious common exposure –Retail food (grocery stores) Cases occur among patrons of restaurant(s) Cases clustered in institution(s) Any combination of above three

December 3, 2008

1 st 11 cases in MN Institutional link, Implication of PB

S. Typhimurium Investigation, November 17-24, 2008 –MDH received 3 outbreak isolates Early December –Leading hypothesis in national investigation was chicken Restaurant-associated outbreak in another state with three PFGE patterns  Ultimately shown to be a “red herring”

Minnesota S. Typhimurium Investigation December 10-19, 2008 MDH received 8 additional outbreak isolates All chicken for first 4 cases traced back - source did not converge with other state’s investigation or with each other First 8 interviewed cases reported eating peanut butter –Suspicious, but not enough evidence to implicate one product, or even peanut butter overall, as the vehicle

Minnesota S. Typhimurium Investigation December 22, 2008 Medical director of LTCF (LTCF A) in northern MN reports confirmed Salmonella infections in 3 residents Specimens from 2 other residents pending –All five cases confirmed with outbreak strain of S. Typhimurium Outbreak cases identified in other institutions

Minnesota S. Typhimurium Investigation LTCF A, LTCF B, elementary school all purchased food from a common distributor in Fargo, North Dakota Only food common to the 3 institutions was King Nut Creamy Peanut Butter Open tub of King Nut peanut butter collected from LTCF A by Minnesota Department of Agriculture on January 5

Week JuneJulyAugSept Cases Cases of Salmonella Typhimurium, by Week of Specimen Collection, Minnesota, June -September, 1995

JuneJulyAugSept Cases PFGE Subtype Restaurant A PFGE Subtype Restaurant B PFGE Subtype Restaurant C Other PFGE Subtypes PFGE Subtype Patterns of Salmonella Typhimurium, by Week of Specimen Collection, Minnesota, June -September, 1995 Week

Selected Enteric Pathogens Reported to MDH, Year Number of Cases Campylobacter Salmonella E. coli O157:H7 Cryptosporidium Shigella

1 confirmed case of salmonellosis = 38 actual cases

Interview Options In person, telephone, mail, e- mail, web-based Rate-limiting step in most outbreak investigations is number of interviewers available to conduct interviews –staff epidemiologist or sanitarian –public health nurses and other professionals –Team Diarrhea

Examine Descriptive Epidemiology Age, gender distribution of cases can give clues to vehicle –e.g., predominately female, median age in 30’s suggests a produce item like lettuce, tomatoes, or sprouts –e.g., predominately school-aged children, young adults often associated with vehicles like ice cream, microwaveable chicken products, etc.

Generate and Test Hypotheses Analytic study designed to test hypothesis –study design based on study questions, resources, and target population –regardless of form of study, intent is to determine whether given exposure led to the occurrence of the disease.

Comparison Groups Gathering/event (e.g., wedding reception) –non-ill attendees Restaurant –well-meal companions, credit card names Cluster of bacterial cases identified through routine surveillance –age-matched controls obtained through sequential digit dialing using case’s telephone prefix –Friends, neighboring households –Population surveys –Cases with similar (but not exact) illness

Analytical Study – Need More than Just a Statistical Association A true exposure should account for high proportion of cases (although in some outbreaks there can be multiple vehicles) Biologic plausibility –right incubation, plausible vehicle, etc. Distribution of cases vs. distribution of food Converging tracebacks Explanation of outliers Watch out for co-linearity

Analytic Study Problems Background rate of consumption is high – chicken, eggs Risk is diffuse – product used in dozens of products Food is “cryptic” or eaten as an ingredient – e.g., spices Not enough interviews completed Interviewer variability Confounding

Sub-Cluster Analyses In large outbreaks, there may be sub-clusters of epi-linked cases – e.g., multiple cases at a restaurant, nursing homes, or school Look for common suppliers and food items Specific analytical studies in these settings

Why Epidemiologic Links May Not be Identified for Cases in a Cluster Cases have imperfect recall Cases may not know they were exposed

Secondary transmission Why Epidemiologic Links May Not be Identified for Cases in a Cluster

Case did not consume product but may have handled it or was exposed through cross-contamination

Why Epidemiologic Links May Not be Identified for Cases in a Cluster Common exposures could be difficult to link –Lack of specific brand information from patient on a common commodity (e.g., eggs, chicken) –Traceback inadequacies Establishment record-keeping Resources available

There isn’t a common source for all of the cases (or any of them) –Stable, endemic strains of various bacteria are present in the animal population e.g., E. coli O157 PFGE subtype associated with Jack-in-the-Box outbreak is still identified in Minnesota each year Why Epidemiologic Links May Not be Identified for Cases in a Cluster

Daily Report from MDH Lab to Epi Cultures Confirmed Yesterday

Daily Report from MDH Lab to Epi Cultures Confirmed or Subtyped in the Past 30 Days