Purpose: Salmonella serotypes are among the most common bacterial causes of foodborne gastroenteritis in the United States, associated with approximately 1.4 million human illnesses annually. Studies on trends of the serotypes and host-related factors are necessary for the development of effective prevention plans for foodborne diseases caused by these pathogens.
Materials and methods: To determine the epidemiologic trends of human infections with the most common Salmonella serotypes in Michigan, we analyzed cases of culture-confirmed salmonellosis at the Michigan Department of Community Health (MDCH) from 1995 to 2001.
Results: A total of 6797 cases were reported, with an average annual incidence per 100,000 population (AAI) of 9.9. Among cases for which information on Salmonella serotype were available (6292 cases), the most common serotypes were S. Typhimurium (1596 cases, 26%), followed by S. Enteritidis (1309, 22%), S. Heidelberg (466, 8%) and S. Newport (222, 4%). From 1998 to 2001, the incidence of S. Typhimurium and S. Enteritidis decreased significantly by 39% (95% confidence interval [CI], 49% to 26% decrease) and 32% (95% CI, 44% to 18% decrease) respectively. Whereas the incidence of S. Newport increased by 101% (95% CI, 25% to 225% increase) and S. Heidelberg remained stable. Infection with these serotypes frequently occurred in the summer months. As a group, infants had the highest AAI for all Salmonella serotypes (75.0), S. Typhimurium (21.9), S. Enteritidis (14.0), S. Heidelberg (5.4), and S. Newport (1.7). Among patients whose race was known, blacks had a significantly higher AAI compared to whites for S. Typhimurium (2.5 vs. 1.3; RR = 2.3, 95% CI, 1.6-3.3), S. Enteritidis (1.4 vs. 1.1; relative rate (RR) = 1.4; 95% CI, 1.1-1.6), S. Heidelberg (0.8 vs. 0.3; RR = 3.6; 95% CI, 2.8-4.6), and S. Newport (0.3 vs. 0.1; RR = 2.8; 95% CI, 1.9-4.2). Among patients whose ethnicity was known, Hispanics had a significantly higher AAI for S. Enteritidis compared to non-Hispanics (1.0 vs. 0.5; RR = 1.9; 95% CI, 1.2-3.0), but not different significantly for S. Typhimurium, S. Heidelberg, and S. Newport.
Conclusion: This study revealed the emergence of S. Newport and the high incidence of the most common Salmonella serotypes among infants, people of African descent, and Hispanics. This information can be used by the state and local health departments of Michigan to enhance salmonellosis prevention efforts by rationalizing the allocation of appropriate public health resources and personnel.