The changing nature of foodborne disease surveillance: a CDC perspective

David W. Warnock, PhD

DirectorDivision of Foodborne, Bacterial and Mycotic Diseases

Centers for Disease Control and PreventionAtlanta, Georgia

Foodborne diseases are a continuing public health concern

● Changes in the pathogens, in the environment, in human tastes, and in the scale of production and distribution have led to new problems

● These problems have created a need for improved surveillance and response

The role of CDC in foodborne disease surveillance

● Foodborne Diseases Active Surveillance Network(FoodNet)– Monitors trends in the burden of illness caused by

pathogens commonly transmitted through food

● National Antimicrobial Resistance Monitoring System (NARMS)– Monitors antimicrobial drug resistance among

enteric pathogens from humans, retail foods, and animals

These programs are organized in collaboration with USDA and FDA

The role of CDC in foodborne disease surveillance

● National Public Health Laboratory-Based Surveillance System– Collects limited information on laboratory-

diagnosed cases of salmonellosis, shigellosis, and Shiga toxin-producing E. coli infection

– Maintains enhanced surveillance for cases of botulism, cholera, listeriosis, typhoid and vibriosis

The role of CDC in foodborne disease outbreak detection and response

● National Molecular Subtyping Network for Foodborne Disease Surveillance (PulseNet)– Detects clusters of enteric illnesses due to

bacterial strains with matching DNA ‘fingerprint’patterns

● Outbreak Network for Foodborne Disease Surveillance and Response (OutbreakNet)– Coordinates investigation of dispersed multistate

outbreaks of foodborne illness to determine which foods are involved and which control strategies are needed

These programs are organized in collaboration with USDA and FDA

The role of CDC in foodborne disease outbreak surveillance

● Electronic Foodborne Outbreak Reporting System (eFORS)– Collects reports of outbreaks of foodborne

disease

● National Outbreak Reporting System (NORS)*– Collects reports of outbreaks of foodborne,

water-borne, zoonotic and person-to-person transmission of enteric disease

* Under development – targeted to be operational from 1.1.2009

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30000

40000

50000

60000

70000

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

7 pathogens

Num

ber o

f sub

mis

sion

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4 pathogens

1996 - E. coli O157; 2000 - Listeria, Salmonella, Shigella; 2004 - Campylobacter, Vibrio cholerae, Yersinia

PulseNet: a decade of development

• Old focal scenario• Large number of cases

in one jurisdiction

• Detected by affected group

• Local investigation

• Local food handling error

• Local solution

• New dispersed scenario• Small numbers of cases

in many jurisdictions

• Detected by lab-based subtype surveillance

• Multistate investigation• Industrial contamination

event

• Broad implications

The spectrum of foodborne disease outbreaks

These changes make coordination among multiple states and agencies even more important than before

● Ensure clinical laboratories do not replace culture with non-culture based diagnostic tests

● Support rapid shipment of isolates from clinical laboratories to state laboratories

● Support real-time ‘fingerprinting’ of isolates at public health laboratories

Enhancing outbreak detection and response:laboratory investigation

Enhancing outbreak detection and response:laboratory investigation

● Improve serotyping methods– Molecular serotyping is easier and cheaper than

traditional methods– The Luminex platform is capable of testing large

numbers of isolates with minimal hands-on time

● Improve ‘fingerprinting’ methods– PFGE is time-consuming, labor-intensive, and

image-based pattern interpretation is subjective – Sequence-based methods (MLVA, SNP) may

offer improved throughput and resolution

● In fall 2007, a multistate outbreak of E. coli O157 in the USA associated with imported beef trim from Canada led to one of the largest ever recalls (21.7 million pounds of ground beef)

● PulseNet USA and PulseNet Canada linked the strains found in beef from the Canadian firm with ground beef in the US plant and with ill persons in both countries

Enhancing outbreak detection and response:PulseNet International

The role of the CDC OutbreakNet Team

● Supports the national network of state and federal public health officials who investigate outbreaks of enteric illnesses

● Works in close partnership with the PulseNet database team

● Helps ensure – Rapid, coordinated detection and response to

multistate outbreaks– Comprehensive outbreak surveillance

15236Multistate clusters identified

84Regulatory activity

84Vehicle implicated3019Epidemiologic investigation

17667Clusters identified29,1685376PFGE patterns submitted

SalmonellaE. coli O157Investigation stage

The new paradigm for foodborne outbreak detection and response

[selected workload statistics from 2005]

Enhancing outbreak investigation and response:epidemiologic investigation

● Make cluster investigation faster and more efficient– Conduct standardized case interviews as

clusters are identified– Develop strategies for conducting rapid

interviews of control persons– Collect case information on-line and store in

standardized electronic database

The current situation contrasts with PulseNet where information on all isolates is stored in a standard electronic database at states, is

transmitted to the national database at CDC, and is available to all participants

Enhancing outbreak detection and response:epidemiologic investigation

● Develop better procedures for investigation of multistate outbreaks, including electronic submission of data to CDC

● Determine cluster characteristics that predict higher potential to detect common source of infection

Enhancing risk-based interventions to prevent foodborne diseases

• USDA and FDA have been working toward a more risk-based approach, in which hazards between the point of production and point of consumption are identified in order to determine where improvements are most needed

• For risk-based interventions be successful, the relationship between consumption of particular foods and illness due to particular agents needs to be understood

• Existing CDC surveillance systems have generated reliable data on the incidence of illness caused by specific enteric pathogens

• No system currently exists to determine routinely the number of illnesses or deaths caused by consumption of particular foods

• Methods are needed to determine the reservoirs (animals, plants, environment) to which foodborne disease can be attributed

Enhancing risk-based interventions to prevent foodborne diseases

Why use outbreak data to attribute illness to various food commodities?

● For most illnesses, the causative food can only be determined if the person was part of an outbreak

● Outbreaks capture information – on both common and uncommon agents– on both common and uncommon food

vehicles

● State and local public health departments report 1200-1400 outbreaks to CDC each year through eFORS

● In 1998, reporting was changed to include more information about food implicated (list of ingredients, method of preparation, and contaminated ingredient)

Why use outbreak data to attribute illness to various food commodities?

Attribution of foodborne illnesses, 1998-2004*

* preliminary data (high, low and most probable estimates)

Beef PorkPoultry

Game

Dairy EggsFruits-

NutsVegeta

blesGrain

s-Bean

sOil-S

ugar FishShellf

ish

● Attribution at point of consumption, not at point of processing, or source

● Broad categories of foods might not represent specific point of contamination– Contamination could be limited to specific foods

within each group of commodities

Limitations of the current attribution model

● The estimates are based on numbers of cases occurring during outbreaks:– Illnesses due to agents that cause many

sporadic cases but few outbreaks, are likely to be under-represented

– Outbreaks that are large, have short incubation periods, or cause more serious illness are likely to be over-represented

Limitations of the current attribution model

Food-related illness and death in the United States

‘We estimate that foodborne diseases cause ~76 million illnesses, 325,000 hospitalizations, and 5000 deaths in the United States each year’

Mead et al. Emerg Infect Dis 1999;5:607-25

This article had been cited on 1511occasions through 3.5.07

● Methods have improved; new and improved data are available

● Updated estimates are needed for decision making

● Revised estimates will be more precise, but because methods have changed:– New estimates cannot be compared with old– New estimates cannot be used to assess

trends

Updating estimates of the number of foodborne illnesses, hospitalizations, and deaths

● Number of persons with Salmonella illness = reported cases X multipliers for under-reporting

● Change in a multiplier: % of ill persons who seek medical care– 1998 estimate (based on 9,000 interviews):

~12%– 2008 estimate (based on 40,000 interviews):

~20%

● Change in this multiplier will decrease estimated annual number of persons with Salmonella illness

Updating estimates of the number of foodborne illnesses, hospitalizations, and deaths

Final thoughts

● There is an urgent need for improvement – In collection of exposure data from ill and well

persons to help state and local officials develop hypotheses and implicate products

– In linkage and analysis of epidemiologic and PulseNet data

– In product information to allow faster trace-back investigation (e.g. lot numbers)

We must shorten the time needed to determine how and where contamination occurred

Thank you for your attentionThe findings and conclusions in this presentation are those of the author and do not necessarily represent the views of

the Centers for Disease Control and Prevention or the Department of Health and Human Services