Shifting Paradigms in Epidemiology: The Expanded Role of the Public Health Laboratory Linda Gaul,...
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Transcript of Shifting Paradigms in Epidemiology: The Expanded Role of the Public Health Laboratory Linda Gaul,...
Shifting Paradigms in Epidemiology: The Expanded Role
of the Public Health Laboratory
Linda Gaul, PhD, MPH
Epidemiologist
Infectious Disease Epidemiology and Surveillance Division
The Old Paradigm
Salmonellosis Outbreak at a Hill Country Ranch,
Texas, 2001
Outbreak Notification
• Infection Control Coordinator at a central Texas hospital called the regional office of the state health department
• ~30 people had presented to the hospital’s emergency room during the previous 24 hours with gastrointestinal symptoms
• All of the ill persons had eaten a picnic supper the previous evening at a local ranch
Components of a Foodborne Illness Outbreak Investigation
• Preliminary epidemiologic investigation: Identification of person, place and time
• Environmental investigation: Assessment of risk factors• Specimen collection and laboratory analysis:
Identification of pathogen• Implementation of control measures: Prevention of
additional cases• Case-control (epidemiologic) study: Identification of
outbreak source• Conclusion and dissemination of findings
Case Definition
• Any three of the following symptoms: Diarrhea, fever, nausea, cramps, vomiting
• Diarrhea defined as > 3 loose stools in a 24 hour period
• OR culture positive stool specimen
• AND ate the picnic supper
Attack Rate
AR (case-defined ill persons) =
109 cases / 215 persons who ate meal =
50.7%
Salmonellosis Outbreak in a Church Camp, 2001
0
10
20
30
40
50
60
70
6/23 A
M
6/23 P
M
6/24 A
M
6/24 P
M
6/25 A
M
6/25 P
M
6/26 A
M
6/26 P
M
6/27 A
M
6/27 P
M
Onset date (by morning or afternoon)
Num
ber
of c
ase-
defi
ned
ill p
erso
ns
Case Control Study and Laboratory Results for Salmonella enterica
Serotype Panama outbreak
Food item Odds Ratio/significance Culture resultsBeans 27.9* N/AJalapenos 2.3 N/ABarbecue chicken 2.2* PositiveOnions 2.1 N/A Barbecue sauce 1.9* NegativeBarbecue brisket 1.6 NegativeSmoked sausage 1.6 NegativePotato salad 1.6 Negative
Food item Odds Ratio/significance Culture resultsPasta salad 1.6 NegativeIced tea 1.6 N/APunch 1.6 N/AColeslaw 1.5 NegativeCorn muffin 1.5 NegativeCorn-on-the-cob 1.3 PositiveIce 1.2 N/ASoda ~1+ N/ABrownies 0.9 Negative
Food item Odds Ratio/significance Culture results Watermelon 0.8 N/ALemonade 0.8 N/AWater 0.8 NegativeOther food items 0.7 N/ACupcakes 0.5 N/A
*Indicates an odds ratio that is statistically significant at the 95% confidence level.+An exact odds ratio could not be calculated because one cell contained zero entries. N/A indicates food not available for testing.
Conclusions• 109 persons developed salmonellosis
following consumption of a bean dish and/or chicken served at a ranch picnic
• Either raw chicken or an ill foodhandler could have been the source of the bacteria
• The beans were cross-contaminated with the bacteria in the kitchen
Pathogen
• Salmonella enterica serotype Panama• Incubation period: 6-72 hours, usually 1-3
days• Symptoms, in descending order of
frequency: Diarrhea, cramps, fever, nausea, vomiting, headache
• Detected in 25 of 37 stool specimens submitted
• Detected in leftover chicken and corn-on-the-cob
Summary: Old Paradigm • Outbreak notification results from detection of
more than the expected number of cases for the place and time
• Pathogen often unknown until after outbreak detection
• Epidemiologic investigation aims at identifying the exposure
• Laboratory results identify the agent and may confirm the epidemiologic findings implicating a source of exposure (food item)
The New Paradigm
Raw Oysters and Typhoid FeverTexas, 2003
Outbreak Notification
• 2 cases of Salmonella Typhi identified in Houston area• Cases had same strain of S. Typhi by PFGE
• 4 additional cases of the same strain reported over the next several weeks• 1 Houston area
• 2 Austin area
• 1 San Antonio
• None of the 6 cases had recent international travel
Components of a Foodborne Illness Outbreak Investigation
• Preliminary epidemiologic investigation: Identification of person, place and time
• Environmental investigation: Assessment of risk factors• Specimen collection and laboratory analysis:
Identification of pathogen• Implementation of control measures: Prevention of
additional cases• Case-control (epidemiologic) study: Identification of
outbreak source• Conclusion and dissemination of findings
Texas cases, typhoid fever strain 309 cluster, 2003
Typhoid Fever, Texas 2003
Case Definition
• Typhoid fever, strain 309, with onset during the summer of 2003
Attack Rate (among interviewed persons)
• Cannot be calculated because number of exposed persons is unknown– AR = # ill / # exposed
Working Hypotheses of Investigation
• Cases have a common exposure
• Vehicle • Unusual food item
• Small number of cases
• Food item not cooked prior to consumption• More than one establishment involved
Epidemiologic Findings
• In-depth exposure histories obtained• Food frequency questions for home eaten food• Categories of restaurants, some specific
examples• Specific questions about raw shellfish
consumption
• All 6 cases identified raw oyster consumption during 5 weeks prior to onset– Specific dates and locations identified
Oyster Traceback and Plant Investigation
• Oysters traced for all 6 cases to the same lease in Galveston Bay
• Samples of frozen product from same harvest area and timeframe, and specimens from oyster plant workers tested negative for S. Typhi
Case Control Study Results for Salmonella Typhi Outbreak
Food item Odds Ratio/significanceRaw oysters 148.2*
Conclusions• 6 cases of typhoid fever were linked to raw
oyster consumption• Implicated oysters were harvested from the
same area of Galveston Bay by the same harvester
• The source of the oyster contamination was not identified• Could have happened during harvesting• Could have happened at the lease site
Pathogen • Salmonella enterica serovar Typhi• Reservoir: Humans• Incubation period: 3 days – 5 weeks• Symptoms: Sudden onset of acute illness,
sustained high fever, severe headache, malaise, anorexia, splenomegaly, rose spots on trunk
• Case-fatality rate 10-20% without prompt antibiotic therapy
• 2-5% of patients become permanent carriers
Summary: New Paradigm • Outbreak notification results from detection
of an increased number of cases of a particular agent or strain of an agent by a laboratory– Pathogen identified at time of outbreak
detection
• Epidemiologic investigation aims at identifying the exposure
Recent Outbreaks Illustrating the New Paradigm
• Spinach-associated E. coli O157:H7 multistate outbreak, Fall 2006
• Lettuce-associated E. coli O157:H7 multistate outbreaks (2), Fall 2006
Recent Outbreaks with Texas Cases Illustrating the New
Paradigm • Peanut butter-associated Salmonella Tennessee
– Outbreak detection based on large number of cases reported to CDC’s PulseNet with unusual serotype of Salmonella and one of 3 similar strains
– Multistate epidemiologic investigation, using common questionnaire, identified 2 brands of peanut butter as suspect vehicles• 2 brands produced in same plant
Recent Outbreaks with Texas Cases Illustrating the New
Paradigm, cont.• 629 lab-confirmed cases in 47 states
reported to date– Onsets 8/1/06 – 4/23/07– Including 24 cases in Texas
• Outbreak strains of organism detected in 21 of 222 tested specimens of peanut butter
• Contamination conditions found in plant, plant shut down for thorough cleanup