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Foodborne Disease and Public Health: Summary of an Iranian–American Workshop
2
Foodborne Disease Surveillance in Iran and in the United States
Moderator: Mohammad Mehdi Aslani
Great strides have been made in the surveillance of foodborne disease over the past few years. This chapter covers three workshop presentations related to surveillance in Iran and the United States: Ali Ardalan’s description of the Iranian Foodborne Disease Surveillance System Pilot Project, with additional details about laboratory testing provided by Nahid Arjmand Kermani; Robert V. Tauxe’s discussion of foodborne disease surveillance in the United States; and Jennifer A. Kincaid’s description of PulseNet USA, the national molecular subtyping network for foodborne disease surveillance in the United States. Following the synopses of these three presentations, the chapter concludes with a summary of the group discussion concerning these topics.
IRANIAN FOODBORNE DISEASE SURVEILLANCE SYSTEM PILOT PROJECT
Presenter: Ali Ardalan,1 with Nahid Arjmand Kermani
Iran is a country with an area of more than 1.6 million square kilometers and a population of approximately 70 million people, 68 percent of whom live in urban areas. It has 30 provinces, 340 districts, and more than 66,000 villages. Iran has nearly 750 hospitals, nearly 8,000 public clinics, and many laboratories, pharmacies, and radiology facilities. The countries
1
Ardalan acknowledged contributions from Hamid Mohaghegh.
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Foodborne Disease and Public Health: Summary of an Iranian–American Workshop
FIGURE 2-1 Map of Iran.
SOURCE: Reprinted with permission from Britannica Concise Encyclopedia, © 2001 by Encyclopedia Britannica, Inc.
that border Iran—and thus can potentially affect the health of its people—include Afghanistan, Pakistan, Turkmenistan, and Iraq (see Figure 2-1). In his presentation, Ardalan provided background information on surveillance in Iran, described the design and preliminary results of a surveillance system pilot project, identified the limitations and strengths of the surveillance system, and proposed future steps that could improve the surveillance.
Background on Surveillance
Surveillance data show that Iran has made great strides in improving health. According to Iran’s Statistical Center, for example, cases of acute diarrhea per year decreased dramatically between 1986 and 1999: from more than 1.6 million in 1986 to fewer than 115 thousand in 1999 (see Figure 2-2).
Among the foodborne diseases monitored for by Iran’s existing surveillance system are typhoid fever, cholera, botulism, and brucellosis. The system requires that any outbreak or epidemic be reported immediately,
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Foodborne Disease and Public Health: Summary of an Iranian–American Workshop
FIGURE 2-2 Number of cases of diarrhea in Iran, 1986–1999.
SOURCE: Iran’s Statistical Center, 2003.
regardless of cause. Figure 2-3 shows the reporting flow for the health care system. (See Chapter 1 for background information on the Iranian health care system.)
In 2004, 16 foodborne illness outbreaks were reported to the Iranian Center for Disease Control. These outbreaks involved a total of 5,804 cases, 793 of which required hospitalization and 5 of which resulted in death. The most commonly identified pathogens were Escherichia coli, Shigella, and Salmonella. Epidemiological studies were conducted for four of the outbreaks.
Recognizing some limitations of the surveillance system, the pilot project described below was designed to encourage the upgrading of the entire system by integrating lessons learned from the pilot project into the national surveillance system.
Project Design
The pilot project described by Ardalan was conducted by the Iranian Research Center for Gastroenterology and Liver Diseases. Field coordination and preparation took place in 2006, and the implementation and data collection occurred from March through May of 2007.
The goal of the project was to develop a model for a national foodborne disease surveillance system. The project had four objectives:
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Foodborne Disease and Public Health: Summary of an Iranian–American Workshop
FIGURE 2-3 Iranian health system reporting flow.
NOTE: HC = health center.
SOURCE: Office for Foodborne and Waterborne Disease Prevention Center/CDC, I.R. Iran.
Estimate the incidence of diarrhea in pilot sites
Determine the etiology of reported diarrhea in the pilot sites
Detect and investigate foodborne and other common-source outbreaks in pilot sites
Assess trends over time
The pilot sites covered a population of 340,000 people. They were located in Pakdahst, a semiarid region in which 57 percent of the population resides in urban areas, and in Damavand, a cold and humid area in which 74 percent of the population is urban. The case definition for diarrhea in adults was at least three loose stools per 24 hours (compared to previous bowel habits) with the occurrence of the loose stools lasting more than 24 hours. For infants the definition was an increased frequency or decreased consistency of the stool compared to previous bowel habits that the mother considered to be diarrhea.
Data-collection instruments included a questionnaire for diarrhea cases, a stool-sample form, and a case-number reporting form. The questionnaire covered signs and symptoms, treatments, contacts, and risk
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factors. A second data-collection form was completed two weeks after the onset of the illness. Recorded data included complications, duration of illness, physician visits, medications, hospitalization, absence from work or school, costs, and whether the illness was fatal.
Laboratory Tests
During the pilot project, health care staffs were asked to provide a stool specimen for every patient who had a diarrheal episode, preferably within 48 hours after the onset of the illness. Samples were to be obtained before the use of any antibiotic and were not to be mixed with urine. For collecting samples from small children, a diaper swab or rectal swab was suggested. Transport media packaging was specified to allow for the testing of different types of organisms. When possible, staff stored the package at 4°C, and the packages were transported to the Research Center for Gastroenterology and Liver Diseases within 2 to 4 hours.
The laboratory detected a variety of bacterial pathogens in the collected samples, including four categories of E. coli (Shiga toxin-producing E.coli, enterotoxigenic E.coli, enteroaggragative E. coli, and enteropathogenic E. coli) and also Salmonella, Shigella, Yersinia enterocolitica, and Vibrio cholerae. Among the protozoa found were Entamoeba histolytica, Giardia lamblia, Cryptosporidium parvum, and Blastocystis hominis. The samples were also tested for rotavirus. Kermani showed slides illustrating the main steps used to detect the organisms, including several steps that used deoxyribonucleic acid (DNA) extraction and polymerase chain reaction.
Preliminary Results
During the three months of the pilot study, 133 cases were reported, nearly half of which involved children younger than 5 years of age. More than one-third of the isolates failed to exhibit any pathogen after being cultured. Rotavirus and E. coli were the most commonly identified pathogens; the reported percentages of Shigella and Salmonella were much lower. None of the cases required hospitalization or resulted in death. Medical treatment varied: Nearly 60 percent of the patients used antibiotics (which are readily available in Iran without prescription); nearly 50 percent used oral-rehydration solution; about 36 percent used anti-diarrhea/cholinergic medicine; 7 percent used herbal medicine; and another 7 percent used medicine that they had prepared for themselves.
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Limitations and Strengths of the System
A variety of factors may have limited the effectiveness of this monitoring and reporting system. Potential limitations include the underreporting of cases, incomplete cooperation by some patients, incomplete cooperation by the staff (especially during the night shift, when the absence of key personnel may be part of the problem), slow transportation of the stool samples, incomplete pathogen identification, and a lack of precise epidemiologic investigations during outbreaks. A lack of knowledge or technical problems in several areas may explain why many attempts to isolate pathogens, including S. aureus and Campylobacter, did not yield positive results. These areas include growth requirements and the proper strategies to be used in collecting, transporting, storing, and processing the samples. The consumption of antibiotics by the patients also may have affected the detection of pathogens in their samples.
The major strength of the pilot project is that, as the first Iranian effort to include both field and laboratory capacities, it provides a good starting point from which to improve the foodborne disease surveillance system in the country.
Closing Remarks—Potential Future Steps
Ardalan proposed a series of steps to improve foodborne disease surveillance in Iran:
Ensure that the surveillance system has been integrated into the health care system
Ensure that the surveillance system contributes to real-time decision making by health managers
Enable the health care system to analyze and interpret the data in the field
Conduct operational research to ensure the feasibility of the model and its adaptability to the current health care system
Improve data collection and transfer, data analysis, laboratory testing, and feedback processes
Improve the ability of the public health care system and of the Research Center on Gastroenterology and Liver Diseases to handle outbreak investigations quickly
Engage and train the community health volunteers
Conduct population-based surveys to obtain such information as the incidence of diarrhea and patterns of health utilization
Design and implement community intervention trials on health education and the prevention of foodborne disease
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Foodborne Disease and Public Health: Summary of an Iranian–American Workshop
FOODBORNE DISEASE SURVEILLANCE IN THE UNITED STATES
Presenter: Robert V. Tauxe
Overview
The Centers for Disease Control and Prevention (CDC), part of the U.S. Public Health Service, is a non-regulatory agency that provides independent scientific assessment to regulatory agencies through the efforts of epidemiologists, microbiologists, statisticians, and other public health professionals. In the 1950s, the CDC established the Epidemic Intelligence Service as an emergency response mission. This program has trained many epidemiologists in the United States and is integral to the agency’s mission. One of the CDC’s roles is foodborne disease surveillance.
In 1997 the CDC estimated that about 36 percent of diarrheal illness in the United States is attributable to foods. It further estimated that approximately 76 million illnesses, 323,000 hospitalizations, and 5,000 deaths each year are attributable to foodborne illness. The United States has a goal of reducing selected foodborne diseases by 50 percent by the year 2010.
Core Concepts and Features of Foodborne Disease Surveillance
Public health surveillance is the ongoing and systematic process of collecting, analyzing, and interpreting disease-specific data for use in the planning, implementation, and evaluation of public health practices. In other words, it is a form of monitoring that is linked to action. There are several reasons to conduct foodborne disease surveillance:
To define the magnitude and burden of diseases that can be prevented or controlled
To identify outbreaks so that control actions can be taken and new problems can be identified
To provide a platform for applied research related to foodborne disease
To measure the effects of control and prevention efforts
In the United States, public health surveillance is complex and occurs at four levels: the clinical level, the county level (approximately 3,500 county health departments), the state level (50 state health departments plus 4 large cities), and the national level (CDC). As illustrated in Figure 2-4, when an ill person visits a health care provider, the flow of information from agency to agency follows a path that depends in part on the disease itself. For some diseases, clinical communication goes straight to the county surveillance office, then to the state epidemiology office and
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FIGURE 2-4 Multi-level structure of public health surveillance in the United States.
NOTE: CDC = Centers for Disease Control and Prevention; Epi = epidemiologists;
PFGE = pulsed-field gel electrophoresis.
SOURCE: U.S. Centers for Disease Control and Prevention.
the CDC. For other diseases, the flow may be from the clinical laboratory to the state public health laboratory. For a very small number of conditions (such as botulism), the CDC offers consultation services 24 hours a day, 7 days a week: any clinician, surveillance officer, or epidemiologist may call to discuss a possible case of botulism immediately. Currently, non-typhoid Salmonella, E. coli O157:H7, and Campylobacter are among the most prevalent causes of foodborne illness in the United States.
More than 250 different diseases can be caused by contaminated foods. Potential sources of pathogens include food, water, animal contact, and contact with other ill or infected persons. The clinical system provides the diagnosis of the particular disease involved. The source can be very difficult to determine in individual cases, but in outbreaks the source can often be identified. The CDC tracks outbreaks of foodborne diseases regardless of which microbe caused them.
In the United States, the costs of surveillance are borne by the particular level of government carrying out the surveillance—county, state, or federal—so the information that is collected must be useful to each level. The states have the basic formal authority for surveillance. An annual meeting of the Council of State and Territorial Epidemiologists sets stan-
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dard case definitions and makes decisions about which diseases to report nationally. All reporting to the national level is voluntary.
Depending on the purpose of surveillance and the support available, the details of the surveillance can vary in a number of ways including the frequency of data collection, the use of rotating versus periodic surveys, and the use of representative sentinel sites. Such sentinel sites are used to obtain more accurate measurements of trends or of the burden of illness and also for the study of sporadic cases.
Enhancements to Foodborne Disease Surveillance
Since 1996, foodborne disease surveillance in the United States has been enhanced in a number of ways. These include improvements in notifiable disease reporting in all 50 states, strengthening of the serotyping of Salmonella and Shigella, the addition of antibiotic resistance monitoring, the initiation of FoodNet (an active sentinel 10-site surveillance system that collects data about sporadic cases), the initiation of PulseNet USA (the national subtyping network for bacterial foodborne pathogens, described in the next section), and the web-based electronic Foodborne Outbreak Reporting System.
With support from the U.S. Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA), the CDC began FoodNet in 1996. The goals of FoodNet are to determine the burden of foodborne illness in the United States, to monitor the trends in the burden over time, to determine which specific foods and settings contribute to that burden, and to develop and assess interventions to reduce the burden of foodborne illness. FoodNet is a collaborative effort and is guided by a steering team with representatives from the CDC, FDA, USDA, and each of the 10 FoodNet sites. Each of these FoodNet sites is a state or a section of a state that is monitored by the state health department, usually in conjunction with an academic school of public health. In 2003, FoodNet covered 14 percent of the U.S. population. Since FoodNet’s inception, the number of pathogens it monitors has increased from 7 to 12; but the very common norovirus is still not covered. The pathogens most commonly identified are Salmonella, Campylobacter, Shigella, Cryptosporidium, and E. coli O157:H7 (Shiga toxin-producing E. coli).
FoodNet uses a variety of methods to estimate the actual number of cases of foodborne illness, which is known to be much higher than the number of diagnosed and reported cases. It performs population surveys to determine the rates of diarrheal illness in the population, the percentage of affected people who seek care, and the percentage of affected people who submit specimens to the laboratory. It also carries out surveys of physicians and laboratories, and it performs active surveillance regard-
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ing culture-confirmed cases and data reported to health departments and the CDC. Using the results from these various approaches, the CDC then assigns multipliers to various steps in the process of estimating rates of occurrence. For example, the general multiplier for Salmonella is 39, meaning that an estimated 39 cases of Salmonella occur for each one that is diagnosed and reported.
Examining Outbreaks of Foodborne Illness
Outbreak investigations can act to improve public health by helping prevent additional cases in a current outbreak, by identifying a new pathogen or problem that is involved in the outbreak, and by determining what can be done to prevent future outbreaks. Outbreaks can be detected at any level of the surveillance system. Furthermore, individuals outside the health system may serve a useful role in outbreak detection by serving an “alert function”—for example, by calling the county health department if they suspect a problem of foodborne illness.
Food can be contaminated at any stage, from production and processing to distribution, final storage, preparation, and cooking. The point at which contamination occurs defines the shape of an outbreak. If contamination takes place during final preparation, cooking, or storage, the outbreak will be focused. By contrast, if the contamination occurs during processing, the outbreak will be diffuse, often covering many states. Characteristics of focused and diffused outbreaks are listed in Table 2-1.
The section on PulseNet USA below contains information about an effective new method for detecting a dispersed outbreak.
TABLE 2-1 Food Outbreak Scenarios
Local/Focused Outbreaksa
Diffused/Dispersed Outbreaks
• Acute large local outbreak
• Diffuse, widespread outbreak
• High dose, high attack rate
• Low dose, low attack rate
• Increase in sporadic cases
• Detected locally
• Detected by laboratory-based subtype surveillance
• Local investigation
• Complex multistate investigation
• Involves a local food handling error, often egregious
• Involves an industrial contamination event
• Local solution
• Industry-wide implications
aA series of local outbreaks may be a manifestation of the widespread distribution of a contaminated food product.
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Closing Remarks
Public health surveillance depends on a system of collaborative networks in which epidemiologists work closely with laboratory personnel. The use of public health laboratory subtyping to detect and investigate diffuse outbreaks has been growing in importance. Identifying and investigating new outbreaks and diseases will require a variety of surveillance strategies and a robust and flexible public health capacity.
The following websites provide additional information related to foodborne illness and surveillance:
FoodNet: http://www.cdc.gov/foodnet
PulseNet: http://www.cdc.gov/pulsenet
Foodborne outbreak surveillance: http://www.cdc.gov/foodborneoutbreaks
CDC Safe Water System: http://www.cdc.gov/safewater
General information about diseases: http://www.cdc.gov/health
PulseNet USA: THE NATIONAL MOLECULAR SUBTYPING NETWORK FOR FOODBORNE DISEASE SURVEILLANCE
Presenter: Jennifer A. Kincaid
Description of PulseNet USA
PulseNet USA, established in 1996, is the national molecular subtyping network for foodborne disease surveillance. Coordinated by the CDC and the Association of Public Health Laboratories, PulseNet USA consists of a national network of state- and local-level public health laboratories and food regulatory agency laboratories. In her presentation, Kincaid provided participants with an informative recent article describing PulseNet USA (Gerner-Smidt et al., 2006).
Laboratories that participate in the network perform standardized molecular typing of foodborne pathogens with pulsed-field gel electrophoresis (PFGE). The CDC houses the resulting databases of PFGE patterns (also called DNA fingerprints), and it makes the databases available to the participating laboratories. Figure 2-5 shows a set of PFGE patterns from E. coli O157:H7.
PulseNet USA has two major roles: 1) detecting foodborne disease case clusters through the use of PFGE, which facilitates the early identification of common source outbreaks; and 2) assisting epidemiologists in their investigations of outbreaks by providing case definition, culture confirmation, and a rapid alert system. It is important to note that PulseNet
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FIGURE 2-5 Pulsed-field gel electrophoresis patterns of E. coli O157:H7.
SOURCE: Centers for Disease Control and Prevention, PulseNet USA.
detects clusters, not outbreaks. A PulseNet cluster is a group of patterns that are indistinguishable by PFGE. It is only after epidemiologists investigate a cluster and find epidemiologic links between its cases that the cluster is classified as an outbreak.
The three basic elements of PulseNet USA all involve data: its acquisition, analysis, and exchange. Participating laboratories use the Internet to upload and download information to and from the main database and server located at the CDC. The successful operation of PulseNet depends upon effective communication, comprehensive quality assurance, and reliable quality-control processes.
Advantages of Pulsed Field Gel Electrophoresis
PFGE serves as the current “gold standard” for molecular typing. It has three major advantages:
It is highly discriminatory.
The universal, relatively simple technique can be used in most laboratories.
If highly standardized, PFGE is a definitive subtyping method.
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Furthermore, with PFGE the time from receiving the isolate to obtaining the result is satisfactory: approximately 4 days (see the discussion regarding rate-limiting steps in the identification of a source at the end of this chapter).
PulseNet USA Activities
Laboratory Network and Databases
The laboratories that participate in PulseNet USA provide PFGE patterns and demographic data to the PulseNet USA national databases. The CDC manages the databases and produces reports. More than 300,000 PFGE patterns have been submitted to PulseNet USA databases, the largest number of which are for Salmonella.
Data Analysis—Cluster Search and Detection
PFGE can be used for molecular subtyping of isolates, which results in an image that is used for analysis. Software tools are used to help compare the PFGE images to find indistinguishable patterns. Cluster detection of cases involves 60-day searches (or, in the case of Listeria, 120-day searches). Once a cluster has been detected, the CDC’s WebBoard is used to post information about it. Participants can then compare PFGE images and information for the identified cluster with PFGE images and information for the cases from their own local area.
PulseNet has greatly improved the ability to identify and investigate dispersed outbreaks. As shown in Figure 2-6, PulseNet detected a 2002 outbreak of E. coli O157 in less than half the time required in 1993. This faster detection allowed for faster recall of contaminated products and helped prevent further illness.
International Efforts
Because the world is now a global community, foods produced in one part of the world may be consumed and cause disease in another part of the world. Consequently, there is a need for effective global early warning systems. Efforts are already underway to establish international collaborations for investigating outbreaks, identifying the sources of problems in laboratories, developing methods to resolve such problems, and developing and validating protocols.
The international family of subtyping networks is growing and now includes PulseNet USA, PulseNet Canada, PulseNet Europe, PulseNet Asia Pacific, PulseNet Latin America, and PulseNet Middle East, which is
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Foodborne Disease and Public Health: Summary of an Iranian–American Workshop
FIGURE 2-6 Illustration of the improvement in the identification of dispersed outbreaks made possible by PulseNet. PulseNet was established in 1996.
SOURCE: Centers for Disease Control and Prevention, PulseNet USA.
the newest network. At least two representatives from Iran plan to attend an update meeting of PulseNet Middle East in Cairo in December 2007.
Closing Remarks
The CDC is looking to the future. Its current PulseNet international collaborations include outbreak investigations; addressing various problems with laboratories, analyses, and protocol development and validation; and the development, evaluation, and validation of new typing methods. Among the methods being developed are a simple non-image-based method to use in conjunction with PFGE; multi-locus, variable-number, tandem assay analysis; and single nucleotide polymorphism analysis.
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Foodborne Disease and Public Health: Summary of an Iranian–American Workshop
DISCUSSION
Throughout the session there were opportunities for questions and comments. Some highlights of the discussions are summarized below.
Standardization of Terminology
Workshop participants discussed the meaning of the term outbreak. One definition is the occurrence of an illness at a higher rate than expected, with the expected rate being specific to the particular illness under consideration. In the U.S. foodborne disease surveillance system, an outbreak is defined as two diagnosed infections causing the same illness and being traced to the same food exposure.
Participants noted that perceptions of diarrhea differ around the world and that an international definition could be useful for surveillance purposes. For young children, the mother’s report of diarrhea generally is clinically useful. For older individuals, diarrhea is generally said to occur if there is a change in the bowel movement involving increased looseness or frequency of the stool, or both. The Burden of Illness network—a group of people who are conducting FoodNet-like surveys around the world—has been working to develop and validate a standard definition of acute gastroenteritis. Reportedly, they have come to agreement and will publish their definition soon.
Iranian Foodborne Disease Surveillance
During the discussion it was noted that Iran has a large private health care sector that is distinct from the public system described in Ardalan’s presentation.
Outbreak Investigation
Mohammad Reza Zali noted that in Iran neither private nor public laboratories or physicians have a legal obligation to make a report to the public health system when pathogens are found in the stool. Field investigation of outbreaks has tended to come a bit late, and in many cases an epidemiologist has not accompanied the team.
The statistical centers at the Iranian universities each have a physician trained for epidemiological investigation. Each university is responsible for covering a specific area of the country. Outbreaks are reported to a deputy, the deputy reports to the university, and the university reports to the Iranian CDC.
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Pilot Study
In response to questions about patient cooperation in the pilot study, Ardalan explained that the most common problem area was obtaining stool samples, and he suggested that educating infected patients about the importance of the samples might help improve cooperation. He also noted that the problem was more common during the night shifts and that the lack of samples at that time might also be related to staffing. Aslani commented that diagnostic laboratories tend to report the result and give it to the patient, but not send the isolate to a public health laboratory.
One of the goals of the pilot project was to convince the Iranian CDC to expand the project nationwide. The pilot study was designed to obtain information to be used in strengthening the capacity for investigations of outbreaks. One aspect of building capacity will be to improve the training of people in the field, including volunteers in small villages.
Reduction in Cases of Diarrhea
The Iranians attribute the remarkable decline in diarrhea from 1986 to 1999 to improvements in their country’s water and sewage systems and in sanitation. Cholera was the only reportable disease covered by the earlier data, but, with improved reporting, investigators are beginning to identify other causes of diarrhea.
PulseNet and FoodNet
International Opportunities
A World Health Organization (WHO) program called Global Salmonella Surveillance includes a set of training courses to which many institutions contribute. Another WHO program offers field epidemiology training. Iranians have been actively discussing and planning to participate in this WHO training program.
PulseNet International is developing subtyping networks in different regions of the world (e.g., PulseNet Middle East). Because Iran has a facility for PFGE subtyping, it may be able to take part in PulseNet Middle East in the future. Kincaid explained that PulseNet Middle East is not yet an official network; rather, it still is in development. Currently the main laboratory involved in PulseNet Middle East is the Oman laboratory, which has been receiving training from the only laboratory in the Middle East that is certified through PulseNet International to perform the method (namely, the Navy-Army Research Medical Laboratory in Cairo). Two representatives from Iran (Dr. Amahti Mohammedi, Chief Director of Reference Laboratories, and Dr. Mohammed Rachbar, Deparment of
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Microbiology Reference Laboratories) are scheduled to attend the second meeting on PulseNet Middle East in Cairo in December 2007.
Testing
Because very many Salmonella strains exist, PulseNet USA sets priorities for when to use PFGE on Salmonella. Isolates from the common Salmonella serotypes receive the highest priority for PFGE subtyping (along with all E. coli O157 isolates). Listeria monocytogenes also receives priority because PFGE is essentially the only way to identify outbreaks caused by this organism. Outbreaks caused by the rare Salmonella serotypes usually can be identified without using PFGE.
PulseNet USA has improved the ability of public health departments to detect clusters of illnesses that may be foodborne disease outbreaks, in part because it brings together subtyping data from many public health departments of states, regions, and countries for comparison. The CDC has developed and standardized the PFGE method, participating laboratories have helped validate the method; the CDC has continuously compared the results and refined the methods as needed, and has published the validated PFGE methods for molecular subtyping of pathogens in PulseNet USA. All PulseNet participating laboratories use standardized protocols, approved equipment, and exactly the same software.
Identification of the Sources of Foodborne Illnesses in the United States
Of the 1,200 to 1,400 outbreaks of foodborne illness reported each year in the United States, the microbial etiology is determined for approximately 60 percent, and a specific food that was the source of the illness is identified in slightly less than half the outbreaks. In a much smaller number of outbreaks, a specific component of the food may be identified as the source of contamination.
The time required to identify the vehicle of the foodborne illness is highly variable. Clusters of cases reported to a health department may make it possible to determine the cause within a few days, but cluster detection may require weeks, months, or even years. In the United States, new rapid DNA-based subtyping methods are being explored, but they are not yet in common use for Salmonella and Campylobacter. Since the PulseNet system requires the isolation of the causative agents of foodborne disease outbreaks, there is often a delay of several days to a week in obtaining PFGE results.
The speed of diagnosis and the speed of the reporting system are also
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critical. In the United States, the rate-limiting steps may include obtaining stool samples from patients and the laboratory testing of stool samples.
The PulseNet system, which focuses on sporadic cases of foodborne illness, has made it possible to detect food sources that might have been common to cases that are widely dispersed geographically. For example, PulseNet made it possible to identify the contamination of eggs and poultry as contributing factors to acquiring salmonellosis and the undercooking of ground beef in the home as a risk factor for acquiring E. coli O157:H7 infection.
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