Occupational Exposure to Streptococcus suis

1. Swine exposed Variable Total (n=73) OD > 2sd (n=2)* Gender Male 56 1 Female 17 1 Nursery/finishing swine Nursery 11 0 Finishing 1 1 Nu rsery and finishing 59 1 No 2 0 Years working with swine 5 - 10 1 0 >10 70 2 Years living in a swine farm Never 2 0 5 - 10 1 0 >10 66 2 Use of gloves s when working with animals Never 19 1 Sometimes 29 0 Most of the times 15 1 Always 1 0 • Occupational Exposure to Streptococcus suis Z-061 Tara C. Smith, Ana Capuano,Brenda Boese, Kendall Myers, and Gregory C. Gray Center for Emerging Infectious Diseases Department of Epidemiology University of Iowa College of Public Health, Iowa City, IA RESULTS SUMMARY ABSTRACT BACKGROUND • Streptococcus suis--swine • Swine pathogen • Causes meningitis in newborn pigs • Transmitted from mother to piglet • Streptococcus suis—human • Sporadic human cases noted • 2005: large outbreak in China due to serotype 2 • 215 infections, 38 deaths [1, 2] • Toxic shock-like manifestation • First reported US case in 2006 [3]. • Swine-exposed individuals had higher mean titers of anti-S. suis antibodies than non-exposed individuals. • Those with the highest titers reported greater than 10 years of working with swine. • 1 individual reported never wearing gloves when working with swine. Streptococcus suis is a gram-positive bacterium that causes invasive disease and death in swine. This bacterium is considered an emerging disease in humans, and was the cause of an outbreak which sickened over 200 individuals in China in 2005. Previously documented human cases of S. suis infection have occurred primarily in those who contracted the bacterium via occupational exposure. Despite a high prevalence in swine, it was only in 2006 that the first human case of invasive disease due to S. suis was diagnosed in the United States. Prior research shows that because S. suis is considered to be typically a swine pathogen and only rarely a cause of human disease, infection is incorrectly attributed to other species of streptococci, including Streptococcus pneumoniae and viridans streptococci. Therefore, we hypothesized that human infections with S. suis are more common than currently recognized. To test this, we analyzed by ELISA the sera of 73 swine-exposed subjects and 67 non swine-exposed subjects in Iowa, testing for antibodies to S. suis serotype 2, the most common serotype to cause disease in humans. Groups’ mean optical densities were compared using generalized linear models. The exposed group presented higher mean optical density at all titer levels. Two swine-exposed observations above 2 standard deviations of the mean were identified. One individual was found to have worked with finish and nursery swine, and the second worked with finishing but not with nursery swine. One of them reported never using gloves when working with sick swine. This suggests that human infection with S. suis occurs more commonly than currently documented, particularly among those in close contact with swine. CONCLUSIONS • S. suis infects humans more frequently than currently recognized. • Swine-exposed individuals are at risk of exposure. • Future studies will further investigate exposure and carriage of S. suis in swine-exposed individuals. STUDY PROTOCOL • Population: • Swine-exposed individuals (n=73) and non-exposed individuals (n=67) from Iowa [4]. • IRB approval was obtained prior to collection. • Questionnaire data: • Individuals completed questionnaires asking about swine exposure and personal protective gear and practices. • Clinical specimens: • Blood samples were collected from all participants. • Molecular methods: • Whole cell enzyme-linked immunosorbant assay (ELISA) using S. suis serotype2. STUDY LIMITATIONS • Samples were not collected specifically for our study, and no samples were collected for bacterial isolation. • No human positive control was available. • Study tested only one serotype (type 2) of S. suis. Additional serotypes may also infect humans; therefore, our data are likely an underestimation of true infection prevalence. • Time period of infection is unknown; therefore, waning antibody • titers in exposed individuals also may underestimate actual infections. Figure 1: Comparison of group mean optical density by dilution, and 95% confidence intervals around mean. WORKS CITED STUDY QUESTIONS DATA ANALYSIS • Sriskandan S, Slater JD. Invasive disease and toxic shock due to zoonotic Streptococcus suis: an emerging infection in the East? PLoS Med 2006;3:e187 • Tang J, Wang C, Feng Y, et al. Streptococcal toxic shock syndrome caused by Streptococcus suis serotype 2. PLoS Med 2006;3:e151 • Willenburg KS, Sentochnik DE and Zadoks RN. Human Streptococcus suis meningitis in the United States. N Engl J Med 2006;354:1325 • Myers KP, Olsen CW, Setterquist SF, et al. Are swine workers in the United States at increased risk of infection with zoonotic influenza virus? Clin Infect Dis 2006;42:14-20. • How frequently does Streptococcus suis infection occur in those in close contact with swine? • Does infection with S. suis vary according to work area and duty? • What are the risk factors associated with infection by S. suis in swine workers? • Optical Density: • Groups’ mean optical density (OD) results were compared using generalized linear models. • The least square mean and 95% confidence interval were calculated per group. • Risk factors associated with prior infection: • Questionnaire data was examined to determine risk factors for infection. * at least in one dilution optical density (OD) greater than two standard deviations above the mean Table 1: Characteristics of swine exposed subjects