Food Protection Trends - April 2009 - (Page 207) TABLE 1. pathogen distribution in foodborne illness outbreaks associated with Mexican food, as reported by the CDC (1990–2006) Etiology Salmonella serovars S. Enteritidis S. Heidelberg S. Typhimurium Other Salmonella Clostridium spp. C. botulinum C. perfringens Norovirus Shigella spp. S. sonnei Other Shigella Staphylococcus S. aureus S. aureus (enterotoxin type A) Escherichia E. coli O157:H7 Enterotoxigenic E. coli Bacillus cereus Campylobacter jejuni Listeria monocytogenes Norwalk virus* Hepatitis A Other and multiple Total 2 10 8 2 4 4 4 4 2 9 215 1 5 4 1 2 2 2 2 1 4 100 Number of outbreaks 74 29 10 10 25 52 1 51 28 13 8 5 11 9 Relative % 34 13 5 5 12 24 0 24 13 6 4 2 5 4 *Norwalk virus is now known as Norovirus food-associated outbreaks was 10 illness cases (range: 2 to 700). The percentage of outbreaks associated with Mexican foods rose slightly over the 16-year period (from 2.4% in 1990 to 2.8% in 2006) for both known and unknown etiology categories (Fig. 1). In some years (2000, 2002, 2003, and 2005) the percentage of outbreaks associated with Mexican cuisine was higher than usual (5% on average). While the total number of foodborne illness outbreaks associated with Mexican foods did not follow any specific trend, there is an increasing incidence of outbreaks associated with this type of food. This may be due to several factors. First, the increasing availability and consumption of Mexican-style food items would logically be expected to lead to greater numbers of illnesses over time. Also, in 1998, the CDC enhanced its outbreak surveillance network, resulting in an increase in the total number of foodborne illness outbreaks reported to the network. It is likely that this action by the CDC resulted in the increase in the number of reports of foodborne illness outbreaks associated with Mexican foods. The majority of outbreaks associated with Mexican foods were placed in the “unknown etiology” category (Fig. 2). Overall, only 215 outbreaks (10,359 illness cases) of the 560 outbreaks in Mexican foods (18,581 illness cases) were positively associated with known causative agents. Among the known pathogens, 34% of the outbreaks were caused by Salmonella, 24% by Clostridium spp., 6% by Shigella spp., 5% by Staphylococcus, and 5% by pathogenic Escherichia coli (Fig. 3). According to the CDC, Salmonella, E. coli O157:H7, and Listeria monocytogenes are among the top five bacteria that cause severe illness (13), and one of these top five bacteria, Salmonella, is often implicated in illnesses associated with Mexican foods. Norovirus (formerly known as Norwalk virus) (13%) was also an important viral agent associated with foodborne illness outbreaks in Mexican foods (Table 1). Foodborne illnesses associated with Mexican foods follow a pattern and are consistently associated with certain microorganisms, based on the 10-year data compiled by Simonne et al. (17) and the findings of this study. Salmonella, Clostridium spp., Shigella spp. and Staphylococcus were the most common pathogens in both studies. However, the prevalence (%) for each bacterium was higher in the first report (17) than in this study. The majority of the Mexican foodassociated outbreaks with known etiologies occurred in restaurants or delicatessens (47%), followed by private homes (16%), schools (6%), workplaces (8%), prisons (3%), unknown, churches or temples and multiple locations (2% each), and other locations (15%) (Fig. 4). The “other locations” category includes hotels, conferences, camps, festivals, fairs, and picnics. The outbreak locations reported in this study are similar to those reported by the CDC and in other studies. According to the CDC, from 1990 to 2006, 50% APRIL 2009 | FOOD PROTECTION TRENDS 207
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