Demographic and cultural influences

The aging of the population in the United States and most other industrialized countries has already altered food-borne disease epidemiology, and is projected to impact food preferences and consumption patterns. By 2020 in the United States, one in five persons will be aged ^65 years. These 71 million individuals will represent 12.4 percent of the population. In 2000, there were 35 million persons ^65 years. Depending on the pathogen, older persons may be more susceptible to clinical illness if infected (e.g. listeriosis); develop more severe disease (e.g. non-typhoidal salmonellosis); be more likely to develop complications (e.g. HUS with E. coli O157:H7 colitis); and be more likely to die (e.g. Vibrio infections). Although hospitalization rates vary by food-borne pathogen, they are usually higher for persons over age 60 years.

In addition to older persons, other populations have distinctly increased susceptibility for food-borne illness (see Table 8.5). Immunocompetent women are at increased risk of listeriosis when pregnant. Infants less than one year of age have the highest age-specific rate of salmonellosis; pre-term infants appear most susceptible to E. sakazakii infection. Persons living with HIV infection and AIDS have more severe salmonella infections and more protracted diarrhea due to cryptosporidium. In the United States, there are an estimated 950,000 persons

Table 8.5 Clinical conditions with increased risk of food-borne infection and illness

• Liver disease, cirrhosis

• Alcoholism

• HIV infection

• Transplantation (solid organ, stem cell)

• Cancer chemotherapy

• Immunosuppressive drugs - corticosteroids, monoclonal antibodies, immune modulators

• Gastric acid suppressing drugs living with HIV infection, and 40,000 new infections occur each year, representing a sizeable vulnerable population.

Perhaps the most significant trend is that of an increasing proportion of the population that is immunocompromized. Transplant recipients are an illustrative example. In 2005, there were nearly 100,000 persons on active waiting lists for solid organ transplant, and 28,108 transplants were performed; 62 percent of these were kidney transplants (OPTN, 2006). Bone marrow transplant recipients are another growing category, with these being performed for an increasing number of hematologic and oncologic conditions. There are an estimated 10 million persons in the United States with renal disease, and the annual number of new cases has tripled over a decade, most due to hypertension and diabetes. In 1997, 360,000 persons were on dialysis or had received renal transplants, and the transplant waiting list had been expanding at 11 percent per year for the past three years (Health and Human Services Department (US), 2000). Advances in earlier detection and treatment have changed the epidemiology of cancer, making it curable for some and converting it to a chronic disease for others. In 1971, there were 3 million cancer survivors in the United States; this had more than tripled to 9.8 million in 2001 (3.5 percent of the population) (CDC, 2004). Chronic diseases such as connective tissue diseases and inflammatory bowel disease are treated with a variety of immunomodulating drugs (e.g. corticosteroids, immuno-suppressive agents, anti-cytokine monoclonal antibodies) which increase susceptibility to infection.

Gastric acid is the first line of defense against food-borne pathogens, and it has been known for many decades that achlorhydria and gastrectomy increase the risk of Vibrio and salmonella infections, as well as tuberculosis. Yet treatment of common conditions such as peptic ulcer and gastro-esophageal reflux (GERD) with acid-blocking drugs neutralizes this primary defense. In 2003, there were 33 million prescriptions for H2 blockers and proton pump inhibitors - which, if administered to unique individuals, would have treated 7 percent of the population. The actual proportion of the population taking acid-blocking medications is likely higher, as these drugs are also available over the counter.

These population groups are increasing at varying rates. Some are new and exist because of medical progress, such as transplant recipients and preterm infants, while others, like the elderly, have always been present but magnify a disease trend because of their increase. Although there is a dearth of data comparing the risk of food-borne illness among these groups, it is likely they are not at equal risk. Some probably bear a disproportionate share of the burden of food-borne illness from individual pathogens. The cost of that disease burden is also measured with newer outcomes - examples being a need for renal transplantation following HUS from E. coliO157:H7, or the rejection of a solid organ transplant precipitated by salmonella infection.

Several cultural trends in the industrialized countries have influenced food-borne illness patterns therein. Congregate settings such as nursing homes and day-care centers have been the site of outbreaks of initially food-borne disease. An amplifier effect is seen with secondary transmission to staff and patients' family members with outbreaks due to E. coli O157:H7 and shigella, both low-inoculum infections capable of being transmitted from person to person in settings where hygiene is inadequate. Petting zoos have emerged as a new location for E. coli O157:H7 outbreaks, with mostly young children acquiring infection from direct contact with ruminant animals and their barnyard environment (CDC, 2005).

The need for behavioral change is evident in the lack of knowledge and consistent practice of food safety habits by the public, as indicated by responses in the periodic surveys of adults in the Behavioral Risk Factor Surveillance System (BRFSS). After handling raw meat, 18 percent of respondents indicated they did not wash their hands (CDC, 1998a). Videotaped observational study showed that consumers tended to underestimate the risk of specific practices, and repeatedly made food handling and sanitation errors (Anderson et al., 2004). Cumulatively, these errors would increase individual risk of food-borne disease over time. One wonders whether these behavioral risks for cross-contamination during food preparation are related to increased consumption of food away from home, and a subsequent lack of familiarity with cooking and safe food preparation practices.

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