In the third session of the workshop, four speakers discussed “sentinel populations”—specific groups within a population that might help to elucidate possible links between food insecurity and obesity. As moderator Mariana Chilton, associate professor in health management policy at Drexel University, pointed out, such groups cannot easily and clearly be bounded. Children, immigrants, American Indians, and rural populations—the four groups discussed in the session—could all be represented in the same household. Nevertheless, focusing on distinct subgroups within an overall population offers a way to examine more closely the relationship between food insecurity and obesity.

YOUNG CHILDREN AS A SENTINEL POPULATION

John Cook, associate professor in the Department of Pediatrics at the Boston University School of Medicine, has been studying children under the age of 3 years in five states as a sentinel population to detect the effects of food insecurity on child health. He began his talk by pointing out, as described in Chapter 2, that the link between food insecurity and obesity is elusive. Although a few studies have found that children living in food-insecure households are more likely to be obese than children who are food secure, most studies have found no evidence of a direct relationship (Larson and Story, 2010). Still, the question remains whether sentinel surveillance of a population of young children could yield useful information about the prevalence or incidence of obesity among different groups, including the overall population of young children, subpopulations of young children, subpopulations distinguished by socioeconomic status (SES) or ethnicity, adolescents, all children, or adults.

Sentinel surveillance is a system in which a prearranged sample agrees to report all cases of one or more notifiable conditions. Such systems have been established for HIV infection, sexually transmitted diseases, influenza, and other diseases. Surveillance involves monitoring the rate of occurrence of specific conditions to assess the stability or change in health levels of a population. The study of disease rates in a specific cohort, geographic area, or population subgroup can point to trends in the larger population, revealing notable changes before they affect the general population, said Cook. A subpopulation may be especially vulnerable to a disease and experience higher disease rates before the general population. It also could be a subpopulation in which the occurrence of or exposure to a disease at one age or life-cycle phase reliably predicts occurrence of disease at a later age or life-cycle phase. “That is the sense in which it makes sense to think of young children as a sentinel population,” Cook said.

The prevalence of obesity varies by age and race/ethnicity (Figure 4-1). The prevalence is not as high for younger children ages 2 through 5 years



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