Older adults at risk of complications from microbial foodborne illness

Food Review, Summer-Fall, 2002 by Jean C. Buzby

Although younger individuals usually face far higher rates of infection from foodborne pathogens (bacteria, fungi, parasites, viruses, and their toxins), older adults, along with the very young and the immuno-compromised, are more likely to have some of the more severe complications from these infections. In particular, some research has shown that the elderly are more vulnerable to gastroenteritis-induced deaths.

Data from the Centers for Disease Control and Prevention's (CDC) FoodNet surveillance system show that for some pathogens, older adults have lower culture-confirmed rates of infection than most or all of the other age groups, despite many age-related factors, such as decreased immune functioning and decreased stomach acid production, that predispose older persons to gastrointestinal infections and their more severe complications. These low rates may be partly due to older persons being more careful about food handling and food consumption than younger persons. Culture-confirmed rates of infection for people over age 60 range from 0.1 cases per 100,000 people for Vibrio and Cyclospora to 10.8 cases per 100,000 people for Salmonella. The infection rates for all Americans range from 0.04 cases per 100,000 people for Cyclospora to 17.4 cases per 100,000 people for Salmonella. Preliminary new FoodNet data from a separate telephone survey on diarrheal disease indicate that adults over the age of 65 have the lowest prevalence of diarrheal disease of any age group for monitored pathogens.

Older adults can benefit from education on safe food handling and food consumption behavior and, in turn, prevent some of the annual foodborne illnesses among this age category. In this article, the term "older adults" refers to individuals age 60 or older, following a category used by FoodNet. The growing number of older adults in the U.S. population suggests that preventing foodborne illness and death among older adults will remain an important challenge.

Foodborne Illness Can Have Secondary Complications

CDC estimates that each year in the United States, nine microbial pathogens cause an estimated 3.5 million foodborne illnesses, 33,000 associated hospitalizations, and over 1,200 deaths (table 1). Data are unavailable on what proportion of these illnesses and deaths afflict older adults.

Most cases of foodborne illnesses are classified as "acute." These cases are usually self-limiting and of short duration, although they can range from mild to severe. Gastrointestinal problems and vomiting are common acute symptoms of many foodborne illnesses. Deaths from acute foodborne illnesses are relatively rare and more typically occur in the very young, the elderly, or persons with compromised immune systems.

The U.S. Food and Drug Administration estimates that 2-3 percent of all acute foodborne illnesses develop secondary long-term illnesses and complications called chronic sequellae. These sequellae can occur in any part of the body, such as the joints, nervous system, kidneys, or heart. One chronic sequella from Campylobacter infections that particularly afflicts older adults is Guillain-Barre Syndrome (GBS), which is an auto-immune reaction that can cause paralysis. GBS may afflict patients for the remainder of their lives and may result in premature death. Other causes of GBS have been documented, such as an auto-immune response to respiratory infections.

Rates of Infection Tell Part of the Story

The 1999 FoodNet data provide information on the annual cases per 100,000 U.S. persons in nine U.S. sites by age distribution for nine foodhorne pathogens (see box on FoodNet). The foundation for these estimates are U.S. foodhorne illnesses that were identified by clinical laboratory tests, or "culture confirmed," and recorded by FoodNet surveillance personnel in each site. To estimate the number of cases per 100,000 people for each age category, the number of reported cases in each age category was divided by the population for each age category according to the 1999 Census population estimates.

According to CDC, FoodNet data have three limitations. First, current reporting captures roughly 13 percent of the U.S. population, meaning that the data may not be nationally representative. Second, FootNet data are limited to laboratory-confirmed illnesses that are reported by surveillance personnel. However, most individuals with foodborne illnesses are never tested to determine the type of pathogen that caused their illness, and even if the illness is laboratory confirmed, an unknown portion of these illnesses is not reported to surveillance personnel. Additionally, individuals of different age groups may not all be tested at the same rate. For example, children may be tested for foodborne illness more frequently than older adults. Third, some laboratory-confirmed illnesses reported to FoodNet can be acquired through nonfoodborne routes, such as contaminated water, person-to-person contact, and direct exposure to infected animals. Therefore, the reported rates do not represent foodborne sources exclusively.