Volume 2, Number 1
Number of hepatitis A cases in the state of Michigan, Calhoun County, and Siginaw County, by month 1997 to date |
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States that received A&W strawberries through the federal school lunch program |
Top National News: Tale of the Outbreak
Editor's Note: The recent hepatitis A incident traced to tainted frozen strawberries from Mexico was the biggest hepatitis news story in decades. We cannot remember another time when viral hepatitis held the news media's attention for weeks at a time. Part of the sensation was surely due to the large size of the outbreak. In Michigan, 264 people became ill, making it one of the largest common source epidemics of hepatitis A reported in the U.S. But it was probably the source of the fruit, the federal school lunch program, that really grabbed the interest of the news media. We Americans expect food supplied by our government to be supremely safe, especially food served to our children. When a breach occurs, it's news.
The outbreak itself was truly serious for those who were ill and their families. But the incident also pointed out the vulnerability of our food supply to microbial contamination, especially food imported from developing countries. That is why we decided to take the unprecedented step of devoting an entire issue of the Hepatitis Control Report to the incident. We also held up publication of the Spring issue to include information that became available only in late June. We based this report on news and wire reports, press releases, scientific papers, presentations at scientific meetings, and interviews with federal, state and local health and agriculture officials. We learned about strawberry farming and packing through conversations with over 20 people in the industry.
The tale is truly interesting and instructive to anyone who works in public health. In our upcoming Summer Issue, we'll resume our regular coverage of news on viral hepatitis. For the Doneth family, of Marshall, Michigan, the story of this outbreak began abruptly. On the morning of Wednesday, March 12, Lindsay Doneth, a 4th grader at Madison Elementary School in Marshall, became ill with body aches, headache, fever, abdominal pain and vomiting. Her mother thought she had the flu and kept her home from school. But, over the next three days, Lindsay's symptoms worsened. By Sunday, the little girl was lying on the couch with severe abdominal pain, afraid to move. Later that day, after she was taken to the emergency room of the local hospital, her mother was shocked to see that Lindsay's urine had turned the color of dark tea. The ER doctor told the Doneths that their daughter had hepatitis, and that several other cases had been confirmed in Marshall in the past two days.
The doctor admitted Lindsay to the hospital and ordered intravenous fluids. By Tuesday, several other people in Marshall had been admitted with hepatitis A, causing a strain on the small hospital's nursing services.
Alarm in Calhoun County
The city of Marshall is located in Calhoun County, Michigan (population 140,000). By the time Lindsay Doneth was admitted to the hospital, county health officials had already become alarmed by a rapid increase in hepatitis A cases. Between March 1 and March 23, 1997, they had received reports of over 100 hepatitis A cases among elementary school children and staff in three different school districts. This was a huge increase in the incidence of hepatitis A. In an average year, the county experienced only about six cases.
The temporal clustering of the cases strongly suggested a common source exposure, but county officials could not identify a common event, water source, or infected food handler. Soon after discovering the outbreak, Calhoun County health authorities administered immune globulin to over 11,000 schoolchildren, staff and contacts.
During the same time that the Calhoun County epidemic was developing, a few cases were also appearing in Saginaw County (population 211,000), located about 120 miles to the northeast. The Saginaw cases were also associated with primary and secondary schools. Officials at the Michigan Department of Community Health (MDCH) initially told the press that they did not believe that the Saginaw cases were related to the epidemic in Calhoun, but they soon changed their opinion in light of new data.
As cases continued to build, MDCH requested help from the federal Centers for Disease Control and Prevention (CDC). On March 23, a team of epidemiologists from CDC arrived to join the investigation, led by Dr. Vitale Pool, of the National Immunization Program, and Dr. Yvan J. F. Hutin, of the Hepatitis Branch, Division of Viral Diseases, National Center for Infectious Diseases. The team quickly confirmed that the outbreak began in Calhoun and Saginaw Counties simultaneously during the week ending March 8. Cases were tightly clustered around the week ending March 22 (see chart), strongly suggesting a common-source exposure about four weeks earlier, around Valentine's Day.
The simultaneous occurrence of two common-source outbreaks in counties 120 miles apart pointed to a remote source of HAV, a source that was not at the level of local food service personnel, but somewhere "upstream" in the distribution, packing, or harvesting of the food. The team soon learned that the only menu item common to all the affected schools was frozen sliced strawberries. The strawberry hypothesis had important public health implications. The berries came from California. They may have been distributed to other states, putting more schoolchildren at risk. But the team could not act until they had solid analytic evidence -and they had to get it quickly.
On March 24, the team began three analytical studies: a case-control study and a retrospective cohort study in Calhoun County, and a smaller case-control study in Saginaw County. Four exhausting days later, after hundreds of telephone interviews with cases and controls, they had their answer. All three studies implicated menu items that contained frozen sliced strawberries. The odds ratios for consumption of strawberry-containing foods in the two case-control studies were high, 6.1 and 7.5, and both were statistically significant.
Two lucky anecdotes also helped pinpoint frozen strawberries as the offender. At one school, a grandfather visited the cafeteria only once during mid-February, and he ate only strawberry shortcake. He became ill about one month later. At another school, a teacher ate at the cafeteria only once -on Valentine's Day -and consumed only hot macaroni and cheese and cold sliced strawberries. The teacher also became a case about a month later. These anecdotes supported the analytic results and boosted the team's confidence that frozen sliced strawberries truly were the vehicle for HAV transmission.
"Oh No, Not Strawberries!"
The investigative team was uneasy about the strawberry association, for good reason. A year before, in June 1996, public health authorities in Texas had identified fresh strawberries as the vehicle for an outbreak of cyclosporiasis. Strawberry sales around the U.S. crashed, causing $40 million in losses for the industry and the loss of 5,000 jobs. After further studies, the actual vehicle for the outbreak turned out to be Guatemalan raspberries, not strawberries. "When strawberries were first mentioned, people said, 'Oh, no,'" CDC investigator Dr. Ian Williams told the Associated Press. "We had to be so careful and take as much time as we could to look at the data before making a conclusion. It was a little intense." But with sturdy epidemiologic evidence in hand, the team confirmed the strawberry association to the federal Food and Drug Administration (FDA) on Friday, March 28.
Because they had already identified the implicated strawberries as supplied by the federal school lunch program, the team also notified the U.S. Department of Agriculture (USDA). The Department's records indicated that the product had come from Andrew and Williamson Sales Company, Inc. (A&W), of San Diego, California. Thirteen lots of A&W strawberries had been shipped in early December 1996 to Michigan and were available for use in the two counties during the exposure period. These 13 lots had been processed at A&W's plant almost a year before the outbreak, on three days in 1996, April 19, May 7 and May 8.
Unfortunately, no records existed in Michigan on which schools received which lots, so it was impossible to know exactly which of the 13 lots had been shipped to the schools that experienced illness. Any one or more of the lots could have contained HAV. FDA labeled all 13 lots as possibly contaminated, prompting an immediate voluntary national recall of the lots by A&W. Frozen strawberries from the same 13 lots had also been shipped to USDA vendors in five other states for use in school lunch programs -Arizona, California, Georgia, Iowa and Tennessee. USDA notified each affected school district. The Department also placed a no-use prohibition on all A&W strawberries, regardless of lot number, in states where they were known to have been shipped to school lunch programs: Florida, Illinois, Indiana, Maine, New Jersey, New York, North Carolina, North Dakota, Utah, Wisconsin and the District of Columbia.
After receiving the news from their team in Michigan, personnel from the CDC Hepatitis Branch spent Friday evening, March 28, telephoning state epidemiologists in the five states that had received strawberries from the Michigan lots. The CDC callers were relieved to hear that no unusual increases in hepatitis A cases had occurred in any of the five states. There was still time to act. CDC recommended that the states give immune globulin to schoolchildren who had eaten from the 13 Michigan lots if it could be given within 14 days of exposure. The clock was ticking, and tracking recipients of the 13 lots would be hectic and difficult.
Pickers, Packers and Processors
Within hours of learning of a possible association with A&W frozen strawberries, state and federal investigators in California followed the paper trail back to A&W's plant in San Diego. FDA inspectors quickly discovered that the strawberries had originated at three farms in Baja California, northern Mexico. This finding had immediate implications. It moved the investigation into the realm of criminal law. USDA rules require that all produce purchased by the federal school lunch program be U.S.-grown. Although this rule has nothing to do with food safety (it was meant to maintain the school lunch program as "Made in the USA" and protect U.S. farmers), it cast a cloud over A&W and its parent company, Epitope, Inc. A&W had signed a certification to USDA that the strawberries were U.S.-grown. Soon after this revelation became public, the president of A&W, Fred L. Williamson, Sr., resigned. The finding also created the potential to turn the matter into an international incident. U.S. relations with Mexico were already strained and did not need another aggravation.
Inquiries at the A&W plant in San Diego were difficult because the strawberry processing operation was closed for the season. Furthermore, no strawberries remained in the freezer from the implicated 13 lots. Investigators found no workers who had been ill with hepatitis-like illness during the three days in 1996 when the lots were processed.
They also learned that the procedures used to pack the strawberries would be insufficient to inactivate all HAV contamination. According to sources in the industry, all U.S. strawberry packers use the same basic method. Strawberries arriving from the fields are run through a tray of water that has been chlorinated at concentrations up to 10 pm (although usually lower). This wash step is very brief, 3-20 seconds. The degree to which the wash solution actually contacts the fruit varies according to the speed at which fruit is passing through the wash. This wash step would not inactivate all HAV located on or in a contaminated berry (see Favero MS, Bond WW. Disinfection and sterilization. In Zuckerman AJ, Thomas HC. Eds. Viral hepatitis: Scientific basis and clinical management. Churchill Livingstone. 1993: 565-75). In an outbreak traced to frozen strawberries in 1990, the wash step apparently did not fully inactive HAV.
Investigators also learned that, after washing, the berries are sorted and culled manually by workers standing over a moving conveyor belt. In some plants, these workers wear latex gloves, but their effectiveness in preventing HAV transmission can vary by how they are used and re-used. Workers are educated to wash their hands frequently, but, as in any part of the food industry, compliance varies.
Soon after rinsing, culling, and, in some cases, slicing, the strawberries are placed in freezers. Sometimes syrups or powdered sugars are added. The product may remain frozen for many months before it is distributed and consumed. Freezing has no adverse effect on the virus. Picking Techniques: Fresh vs. Frozen Strawberries Within days of arriving at A&W's plant in San Diego, federal inspectors traveled to northern Mexico to inspect the fields where the strawberries were picked. According to Fred Shank, director of the FDA's Center for Food Safety and Applied Nutrition, the strawberries were grown in highly unsanitary conditions. He said, "Open and unlined pit privies were placed immediately adjacent to the fields; there were too few [toilet] facilities for the picking crews and there were no handwashing facilities."
Agency officials also confirmed that strawberries destined for freezing or other processing are picked in a way that makes them more vulnerable to microbial contamination than fresh strawberries. Fresh strawberries are picked before they are fully ripe, and are severed from the plant at the stem, above the calyx (the green cap at the top of the berry). On the other hand, strawberries destined for freezing are picked when they are fully ripe, and are detached from the plant under the calyx. Sometimes this is done easily by merely holding the fruit and pulling. At other times (sometimes dependent on the strawberry variety), mere pulling is not effective, and the strawberries must be incised slightly by sticking a finger or fingernail under the calyx. Strawberry farmers are docked for defects in their berries as they arrive at the packing plant. A strawberry that has been picked for freezing is defective if any internal stem remains in the fruit, below the calyx. Farmers warn their pickers to remove all internal stem from the berry. To do this, the picker must sometimes manipulate the fruit to be sure the stem is completely gone.
Mexican Officials Unhappy
As the Mexican origin of the berries hit the news, Mexican agriculture officials reacted indignantly. "It is more likely that the strawberries were contaminated, if they were contaminated, during processing and packing rather than during cultivation," one Mexican official told the Associated Press. He said that farmers in Baja California use deep well water to provide clean water for irrigation, and that there is an "extremely rigorous procedure for handling fruit, and even more so when it is for export."
Another official, Dr. Cipriano Aquilar Aguayo, director of Baja California's Coordinated Health Services, said there were no reports of outbreaks of hepatitis A nor any increase in the number of cases in the area. Yet another Mexican official told Reuters that "a [processing] plant that commits the offense of using an imported product in a program in which it is banned, tantamount to contraband, could also be suspected of breaking standards, such as sanitary levels." Back in the U.S., the outbreak was commanding attention at the highest levels of the federal government. Each day during the crisis, a special conference call took place among top officials of the Departments of Health and Human Services and Agriculture, as well as the office of the FDA Commissioner, the CDC Director and a collection of epidemiologists and agriculture officials. President Clinton received a briefing memo on the incident from Health and Human Services Secretary Donna Shalala and Agriculture Secretary Dan Glickman, and the President's Press Secretary discussed it at a White House briefing.
Detective Work in the States
The response was swift in the five states where the 13 lots had been shipped to federal food lunch programs. Although no outbreaks caused by frozen strawberries had yet occurred in those states (weeks later, CDC confirmed that no cases occurred in any state except Michigan), thousands of children had consumed berries from the 13 implicated lots within the previous two weeks. CDC had recommended immune globulin prophylaxis for such children. If the states moved quickly, they could prevent outbreaks due to recent consumption.
By April 2, California epidemiologists had discovered that the strawberries were served in fruit cups at 18 schools in the Los Angeles school district from March 25 through March 28, well within the two-week window of effectiveness for immune globulin. That same day, students in Los Angeles went home with consent forms and educational packets about hepatitis A in five languages. Immune globulin shots began the following morning and, by the end of the week, 9,000 children had received injections. This huge shot program garnered nationwide news coverage.
In Georgia, officials found that the implicated strawberries had been served in about 30 school systems, all in southeast Georgia. County health officials gave immune globulin to anyone exposed within the previous two weeks. By the second week in April, over 10,000 Georgia students had been given shots of immune globulin. In Tennessee, the departments of health and education conducted a survey of county school districts. Only six counties had used any of the 13 lots within the previous two weeks. Immune globulin was given to 8,600 children in those counties, mostly in southeastern Tennessee.
Iowa took a somewhat different approach. There, state health officials quickly determined that only three of the 13 lots had reached the state, and, as in other states, there was no way to know if these three lots actually carried HAV. A survey by the state education department showed that fruit from the three lots had been served in 25 Iowa schools since as far back as January, with no cases of hepatitis A reported in any of the schools. Based on these findings, Iowa decided against administration of immune globulin.
In Arizona, disease control workers determined that the state's schools had received strawberries from five of the 13 Michigan lots. The Arizona Department of Education traced which schools had actually served the berries and when they had been consumed, an enormous amount of work. According to State Epidemiologist Dr. Bob England, most of the over 300 school districts in Arizona had received frozen strawberries from the implicated lots, and had been serving them since as early as December. Immune globulin was given only in two schools and one Headstart class, where the exposure was recent. As in many other states, Arizona had great difficulty in locating adequate doses of immune globulin. Meanwhile, back in Michigan, investigators found that the strawberries had been distributed to school districts in 28 counties. They had also been served at a Special Olympics event in Grand Rapids on March 22. Immune globulin was offered to all 1,400 attendees. Additionally, the berries had been distributed to the general public through a commercial distributor.
Distribution records from A&W showed that only about 40 percent of the 2.6 million pounds of strawberries processed on the three days in question were sold to the USDA. The remaining 60 percent were distributed commercially and were already being used by consumers in several states. Although A&W had agreed to recall all strawberries that had hit the commercial market, in many cases this was difficult or impossible. Worried officials were comforted by the knowledge that many of the strawberries that entered the commercial market probably ended up pasteurized or otherwise cooked, thus inactivating HAV.
Despite heightened surveillance, no outbreak-associated case of hepatitis A was identified in any state except Michigan. Although it is possible that the massive immune globulin campaigns prevented cases, it is also possible that, for reasons not understood, the HAV contamination was concentrated in a relatively small part of the lots sent to Michigan.
Legalities
Legal problems at A&W mounted quickly. Six days after the resignation of the company's president, A&W's parent company, Epitope, Inc., took legal action to reverse its December 1996 purchase of A&W. In early June, A&W was indicted on federal charges that it concealed the fruit's Mexican origin, in violation of USDA rules. The company has denied the charges, saying, "we believed we were following the law."
Recently, A&W announced that its original owners had reclaimed the company from Epitope, and that Fred L. Williamson, Sr. had been reinstated as CEO. The company also said that it is instituting a new field-to-customer quality assurance program, and that it has "made sure our insurance company paid for the inoculation of any schoolchildren at risk" (The Packer, June 23, 1997).
In Michigan, United Press International reported on April 9 that fifteen lawsuits on behalf of 34 plaintiffs were filed in Calhoun County against A&W and Epitope. The suits allege that the companies were negligent and that they violated the state's Consumer Protection Act. Also on April 9, Reuters reported that a class action lawsuit was filed against the two companies on behalf of all students in the Los Angeles area exposed to HAV through contaminated strawberries. That suit seeks compensation for students and their parents, as well as punitive damages and a sum for a "medical monitoring fund."
DÈjý Vu
Although the news media covered the strawberry incident intensively, very few stories mentioned that Michigan's was not the first multi-state epidemic of hepatitis A caused by frozen strawberries. A similar incident occurred in 1990, in which two outbreaks, in Georgia and Montana, were traced to frozen strawberries. Those strawberries, however, were grown and picked in the U.S. The 1990 outbreak involved 15 people sick with hepatitis A at an elementary school in Murray County, Georgia and 13 people sick at an institution for the developmentally disabled in Jefferson County, Montana. The implicated frozen strawberries were packed almost two years earlier at a plant in California. After processing and freezing, the strawberries were distributed nationwide. Investigators from CDC confirmed the source of the disease in each state through two case-control studies. Also, they found that the nucleic acid sequence of the HAV RNA in the Georgia outbreak was identical to the HAV RNA in the Montana outbreak.
The strawberries in the 1990 outbreak were processed in one evening shift. The manufacturer recalled all lots processed during that shift. No plant workers or field workers were known to have hepatitis during the time in question, and the exact source of the contamination was never determined. Dr. Manette Niu and her colleagues reported that "contamination probably did not occur from an infected worker within the processing plant but most likely from an infected picker (J Infect Dis 1992;166:518-24)."
The 1990 outbreak received little media attention at the time, in part because it was much smaller than the Michigan outbreak and in part because it did not involve the federal school lunch program.
Epidemiologic and Economic Tallies
On June 3, 1997, CDC confirmed that the precise source of the contamination was not known and may never be known. The agency's analysis suggests that the contamination occurred before the strawberries arrived in Michigan, but investigators have not been able to pinpoint whether HAV contaminated the fruit during irrigation or picking in Mexico, during packing in San Diego, during subsequent processing, or by some other route. CDC also confirmed that outbreak-associated cases occurred only in Michigan. Investigators were still reviewing hepatitis A cases in Maine (N=36), Louisiana (N=12), Wisconsin (N=5) and Tennessee (N=1), but no association with strawberries had been established in those states.
In Michigan, 264 cases of hepatitis A were associated with the outbreak, 242 in Calhoun County and 22 in Saginaw County. At the end of May, 17 percent of the Calhoun County cases had been identified as secondary; i.e., contacts of primary cases. No deaths occurred as a result of the outbreak, according to Dr. David R. Johnson of MDCH. Approximately 10 percent of the cases were hospitalized. One patient, a second-grade teacher in Marshall, Michigan, experienced hepatic coma and was airlifted to the University of Michigan's liver critical care unit. She later recovered. Dr. Johnson estimated the public health cost of the outbreak to state and local agencies in Michigan at nearly $475,000 in person hours and other resources, including $110,895 for immune globulin. Other states have not yet reported their public health costs.
Policy Aftermath
By coincidence, publicity about the strawberry incident erupted on the same day that federal agencies were meeting in Washington to discuss President Clinton's National Food Safety Initiative. Reportedly, the incident prompted agency and White House staff to add hepatitis A to the list of foodborne diseases that will receive special attention under the Initiative. If the Initiative, now renamed "Food Safety from Farm to Table," is approved by Congress, CDC will receive badly-needed funds and staff positions for research in HAV genetic epidemiology, for a large hepatitis A case-control study and for expansion and improvement of viral hepatitis surveillance (for further details on the Initiative, see FDA's web site, WWW.fda.gov). In May, USDA announced an 11-step plan to assure that imported produce will never again be purchased by the the federal school lunch program. Members of Congress have proposed legislation that would stiffen the penalties for suppliers who lie about the origin of USDA food. These are necessary steps, but it is unclear how much protection they can actually provide against another multi-state HAV incident. The 1990 frozen strawberry outbreak proved that U.S. origin is no guarantee against HAV contamination of produce. More importantly, even if foreign produce never again infiltrates the federal school lunch program, American school children will continue to eat foreign-grown fruits and vegetables often -at home, in restaurants and in non-USDA lunches at school. In a May 29 editorial in the New England Journal of Medicine, Dr. Michael Osterholm, State Epidemiologist in Minnesota, observed that, in some seasons, up to 70 percent of selected fruits and vegetables consumed in the U.S. come from developing countries.
Produce-Associated HAV Outbreaks: Rare but Costly
Although the frozen strawberry incident brought hepatitis A to the attention of the American public in a very vivid way, these incidents actually represent only a tiny risk to consumers. Most Americans consume uncooked fresh and frozen produce on a daily basis, either as a ready-to-eat food or as a component of other foods. Despite this high level of exposure, only three outbreaks have been reported in the U.S. during the past ten years involving fresh or frozen produce contaminated "upstream" from the local foodhandler. These three outbreaks involved a total of 494 cases of hepatitis A, a minuscule proportion of the more than 250,000 cases reported in the U.S. during the same period.
In addition to the two frozen strawberry-associated outbreaks, one outbreak was traced to iceberg lettuce in 1988. In that epidemic, 202 cases occurred mostly among diners who ate green salad at one of three restaurants, which were supplied by the same fresh produce distributor. CDC investigator Dr. Lisa Rosenblum and her colleagues concluded that contamination of the lettuce probably occurred before local distribution to the restaurants (Am J Public Health 1990;80:1075-79). One non-U.S. outbreak was reported from Scotland in 1987 by TM Reid and HG Robinson (Epidemiol Infect 1987;98:109-12), involving frozen raspberries.
Although rare, incidents such as the recent one are truly costly in economic terms. As mentioned above, the public health cost in Michigan alone was nearly $475,000. The total public health cost in the U.S. is sure to be substantially more. For immune globulin alone, at least 38,000 doses were administered by public health and school agencies in states that received the 13 implicated lots. Assuming $15 per dose, the total cost of these shots exceeded $575,000. The total societal cost of the incident would include these public health costs, plus other direct and indirect costs borne by patients, families, schools, businesses, insurance companies and governmental agencies. Prevention
How can such outbreaks be prevented in the future? There is no quick fix, partly because the exact mechanism of contamination in these outbreaks remains unknown. In her report on the 1990 frozen strawberry-associated outbreak, Dr. Niu and her colleagues wrote that "the mainstay of prevention of hepatitis A is strict attention to hygiene and sanitation at all levels of food preparation. For fruits and produce that are served raw, this requires a high level of sanitation during picking, processing, packing, and food preparation. Workers harvesting fruit and produce must have the same access to hand washing and bathroom facilities as food handlers who process, package, and prepare these items. Hepatitis A immunization of certain high-risk groups, including food handlers, and selected institutionalized persons may be beneficial in preventing similar outbreaks." Experts in public health and food safety continue to suggest a multi-pronged strategy: strengthened environmental and sanitary procedures in the growing fields and processing plants, better worker education on basic hygiene such as handwashing, and improved barrier, decontamination and pasteurization methods. To truly protect U.S. consumers, these components would have to be implemented both in this country and in exporting countries.
Dr. Niu's suggestion that hepatitis A immunization of foodhandlers might be beneficial has not yet been tested for feasibility and cost-effectiveness in the produce industry. Vaccinations have begun in the restaurant industry (see Hepatitis Control Report, Winter 1996-97), and one state, Minnesota, recently recommended hepatitis A vaccination for foodhandlers. But only Virginia has begun vaccinating migrant farm worker families. In the short term, vaccination of produce workers will probably be most attractive to individual growing and packing companies that are highly risk-sensitive and that seek "insurance" against the risk of HAV contamination. These vaccination programs will have to include pre-vaccination testing, since most adult produce workers were probably infected during childhood and are anti-HAV seropositive. In the future, the risk of acquiring HAV infection through food will be gradually eliminated by universal hepatitis A vaccination. ACIP endorsed this approach in 1996, while pointing out that it will not become feasible until hepatitis A vaccine is licensed for use in children under 2 years of age, and until combination vaccines containing hepatitis A antigen are available (see Hepatitis Control Report, April 1996).
Until then, it is reasonable to expect that rare outbreaks of hepatitis A caused by contamination of uncooked fruits and vegetables at the distributor, packer, or picker levels will continue to occur. Theoretically, they could actually increase in frequency. Living conditions are improving south of the U.S.-Mexico border, causing HAV infection to be postponed into older age groups. As more people begin work in the produce industry still susceptible to the virus, the risk of food contamination could theoretically increase.
Prevention efforts have already started and will continue. FDA recently organized a meeting in Tijuana with representatives from USDA, CDC, the State of California, and growers and officials from Mexico to help resolve sanitation problems in Mexican fields. U.S. growers and packers are pursuing several other avenues that will help reduce the risk of another HAV contamination incident.
Back in Marshall, Michigan, Lindsay Doneth is pretty much over her bout with HAV, although she still feels fatigued at times. Her mother, Susan, was so shaken by the outbreak that she has since become an avid food safety crusader.
Editor's Comment: The response of our public health system to this incident was, by every account, rapid, well organized and effective. Federal, state and county health agencies worked extraordinary hours for weeks to trace the cause of the contamination and prevent further infections. They should be commended, and consumers should be reassured that our public health system can expertly manage an interstate alarm.
On the other hand, it is not difficult to imagine a future outbreak of this kind occurring in many more states, with many more cases. Indeed, one of the mysteries of the recent incident is why HAV did not spread more widely. We simply do not know what factors determine the quantity and distribution of virus in contaminated foods. As prevention efforts proceed, more epidemiologic and virologic research is needed to determine the mechanism of these outbreaks.