Exposure to Streptococcus suis among US swine workers.

Despite numerous cases of human infection with Streptococcus suis worldwide, human disease is rarely diagnosed in North America. We studied 73 swine-exposed and 67 non-swine-exposed US adults for antibodies to S. suis serotype 2. Serologic data suggest that human infection with S. suis occurs more frequently than currently documented.

Testing human sera for antibodies against avian influenza viruses: horse RBC hemagglutination inhibition vs. microneutralization assays.

BACKGROUND: The hemagglutination inhibition (HI) assay is a frequently used method to screen human sera for antibodies against influenza A viruses. Because HI has relatively poor sensitivity in detecting antibodies against avian influenza A strains, a more complicated microneutralization (MN) assay is often preferred. Recent research suggests that the sensitivity of the HI assay can be improved by switching from the traditionally used turkey, guinea pig, human, or chicken RBCs to horse RBCs. OBJECTIVE: To evaluate the performance of the horse RBC HI when screening for human antibodies against avian influenza types H3, H4, H5, H6, H7, H9, H11, and H12. STUDY DESIGN: We evaluated the reproducibility of horse RBC HI and its agreement with MN results using sera from people exposed or not exposed to wild and domestic birds. RESULTS: The horse RBC HI assay had high reliability (90%-100%) and good agreement with MN assay results (52%-100%). CONCLUSION: The horse RBC HI assay is reliable, less expensive, less complex, and faster than the MN assay. While MN will likely remain the gold standard serologic assay for avian viruses, the horse RBC HI assay may be very useful as a screening assay in large-scale epidemiologic studies.

Cases of swine influenza in humans: a review of the literature.

As the threat of a pandemic looms, improvement in our understanding of interspecies transmission of influenza is necessary. Using the search terms "swine," "influenza," and "human," we searched the PubMed database in April 2006 to identify publications describing symptomatic infections of humans with influenza viruses of swine origin. From these reports, we extracted data regarding demographic characteristics, epidemiological investigations, and laboratory results. We found 50 cases of apparent zoonotic swine influenza virus infection, 37 of which involved civilians and 13 of which involved military personnel, with a case-fatality rate of 14% (7 of 50 persons). Most civilian subjects (61%) reported exposure to swine. Although sporadic clinical cases of swine influenza occur in humans, the true incidence of zoonotic swine influenza virus infection is unknown. Because prior studies have shown that persons who work with swine are at increased risk of zoonotic influenza virus infection, it is prudent to include them in pandemic planning efforts.

Infection due to 3 avian influenza subtypes in United States veterinarians.

BACKGROUND: Pandemic influenza virus strains originate in avian species. We examined veterinarians in the United States for evidence of previous avian influenza virus infection. METHODS: We performed a controlled, cross-sectional seroprevalence study among 42 veterinarians and 66 healthy control subjects using serum samples collected from 2002 through 2004. Serum samples were tested using a microneutralization assay against 9 influenza A virus strains. RESULTS: Using multivariable logistic regression modeling, veterinarians exposed to birds demonstrated statistically significant elevated titers against the H5, H6, and H7 avian influenza virus isolates, compared with control subjects. CONCLUSIONS: These data suggest that occupational exposure to avian species may increase veterinarians' risk of avian influenza virus infection. Veterinarians should be considered for priority access to vaccines and antiviral drugs in pandemic planning.

Are swine workers in the United States at increased risk of infection with zoonotic influenza virus?

BACKGROUND: Pandemic influenza strains originate in nonhuman species. Pigs have an important role in interspecies transmission of the virus. We examined multiple swine-exposed human populations in the nation's number 1 swine-producing state for evidence of previous swine influenza virus infection. METHODS: We performed controlled, cross-sectional seroprevalence studies among 111 farmers, 97 meat processing workers, 65 veterinarians, and 79 control subjects using serum samples collected during the period of 2002-2004. Serum samples were tested using a hemagglutination inhibition assay against the following 6 influenza A virus isolates collected recently from pigs and humans: A/Swine/WI/238/97 (H1N1), A/Swine/WI/R33F/01 (H1N2), A/Swine/Minnesota/593/99 (H3N2), A/New Caledonia/20/99 (H1N1), A/Panama/2007/99 (H3N2), and A/Nanchang/933/95 (H3N2). RESULTS: Using multivariable proportional odds modeling, all 3 exposed study groups demonstrated markedly elevated titers against the H1N1 and H1N2 swine influenza virus isolates, compared with control subjects. Farmers had the strongest indication of exposure to swine H1N1 virus infection (odds ratio [OR], 35.3; 95% confidence interval [CI], 7.7-161.8), followed by veterinarians (OR, 17.8; 95% CI, 3.8-82.7), and meat processing workers (OR, 6.5; 95% CI, 1.4-29.5). Similarly, farmers had the highest odds for exposure to swine H1N2 virus (OR, 13.8; 95% CI, 5.4-35.4), followed by veterinarians (OR, 9.5; 95% CI, 3.6-24.6) and meat processing workers (OR, 2.7; 95% CI, 1.1-6.7). CONCLUSIONS: Occupational exposure to pigs greatly increases workers' risk of swine influenza virus infection. Swine workers should be included in pandemic surveillance and in antiviral and immunization strategies.