Integrated food chain surveillance system for Salmonella spp. in Mexico

Abstract

Few developing countries have foodborne pathogen surveillance systems, and none of these integrates data from humans, food, and animals. We describe the implementation of a 4-state, integrated food chain surveillance system (IFCS) for Salmonella spp. in Mexico. Significant findings were 1) high rates of meat contamination (21.3%-36.4%), 2) high rates of ceftriaxone-resistant S. Typhimurium in chicken, ill humans, and swine (77.3%, 66.3%, and 40.4% of S. Typhimurium T isolates, respectively), and 3) the emergence of ciprofloxacin resistance in S. Heidelberg (10.4%) and S. Typhimurium (1.7%) from swine. A strong association between Salmonella spp. contamination in beef and asymptomatic Salmonella spp. infection was only observed in the state with the lowest poverty level (Pearson r = 0.91, p<0.001). Pulsed-field gel electrophoresis analysis of 311 S. Typhimurium isolates showed 14 clusters with 102 human, retail meat, and food-animal isolates with indistinguishable patterns. An IFCS is technically and economically feasible in developing countries and can effectively identify major public health priorities.

Figure 1

Percentage of human, retail meat, and food-animal samples positive for Salmonella spp. detected by an integrated food chain system in Mexico, 2002–2005. Numbers to the right of bars indicate average values, and numbers in parentheses indicate the frequency of positive samples in the states with the lowest and highest prevalence, respectively. The number of specimens examined from each source (n) is shown next to each source heading.

Figure 2

Selected pulsed-field gel electrophoresis (PFGE) clusters that represent 102 strains of Salmonella Typhimurium and shared indistinguishable PFGE patterns among humans (H), chicken meat and intestine (C), pork meat and swine intestine (P), and beef meat and cattle intestine (B). Several clusters (C,D, E, and L) were present in more than one state. MI, Michoacan; SLP, San Luis Potosi; SO, Sonora; YU, Yucatan. An expanded version of this figure containing the complete set of PFGE patterns is available from http://www.cdc.gov/EID/content/14/3/429-G2.htm.