Abstract
Salmonella infections cause an
estimated 94 million illnesses worldwide annually and are the
leading cause of hospitalization and death from US
foodborne illness. Serotyping yields important information
for Salmonella public health surveillance. Although most
illnesses represent sporadic infections, surveillance of
salmonellosis outbreaks provides valuable insight into transmission
routes of Salmonella infection if a source can be
implicated. The serotype distribution among all Salmonella
laboratory isolates reflects a variety of sources and not just
foodborne transmission (estimated 55-95% of illnesses). We used
data from the US Foodborne Disease Outbreak Surveillance System to
examine secular trends in serotype distribution specifically within
foodborne salmonellosis. We calculated proportions of foodborne
salmonellosis outbreaks caused by each serotype within 9 time
periods from 1973-2012 with bootstrap 95% confidence intervals
(CIs) and compared these with proportions of serotypes among
laboratory isolates from the National Salmonella
Surveillance System, which reflect all transmission routes. Among
3,326 salmonellosis outbreaks with a single, known serotype, 72%
were caused by the 4 most common serotypes (Enteritidis,
Typhimurium, Heidelberg, and Newport). Of 90 serotypes reported, 28
caused 10 outbreaks or more (94% of outbreaks). Serotype
Enteritidis caused 9% (95% CI 4-13%) of outbreaks from 1973-1977,
68% (95% CI 63-73%) from 1993-1997, and 30% (95% CI 26-34%) from
2008-2012. From 1993-1997 to 2008-2012, serotypes Typhimurium (11
percentage points), Newport (9), and Javiana (3) exhibited the
largest increases in proportions of outbreaks. The proportion of
outbreaks caused by serotype Enteritidis was higher than the
proportion of isolates that were Enteritidis in each time period
(maximum difference: 70% of outbreaks vs. 26% of isolates in
1993-1997), whereas proportions of outbreaks were lower than
proportions of isolates in nearly all time periods for serotypes
Typhimurium, Newport, and Javiana, suggesting that non-foodborne
transmission might be more common for these serotypes since they
were underrepresented among foodborne disease outbreaks. Given that
the overall incidence of salmonellosis has not declined in the past
decade despite intensive efforts, information
about these secular trends in serotypes
and foodborne disease outbreaks
may be useful in guiding future control and prevention
strategies.
Table of Contents
Section, Page
Background/Literature Review, 1
Methods, 4
Results, 8
Discussion, 11
Future Directions, 18
References, 19
Figures, 24
Tables, 28
Supplemental Figures, 30
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