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Background: Defining the primary characteristics of persons infected with hepatitis C virus (HCV) enables physicians to more easily identify persons who are most likely to benefit from testing for the disease. Objective: To describe the HCV-infected population in the United States. Design: Nationally representative household survey. Setting: U.S. civilian, noninstitutionalized population. Participants: 15 079 participants in the National Health and Nutrition Examination Survey between 1999 and 2002. Measurements: All participants provided medical histories, and those who were 20 to 59 years of age provided histories of drug use and sexual practices. Participants were tested for antibodies to HCV (anti-HCV) and HCV RNA, and their serum alanine aminotransferase (ALT) levels were measured. Results: The prevalence of anti-HCV in the United States was 1.6% (95% CI, 1.3% to 1.9%), equating to an estimated 4.1 million (CI, 3.4 million to 4.9 million) anti-HCV-positive persons nationwide; 1.3% or 3.2 million (CI, 2.7 million to 3.9 million) persons had chronic HCV infection. Peak prevalence of anti-HCV (4.3%) was observed among persons 40 to 49 years of age. A total of 48.4% of anti-HCV-positive persons between 20 and 59 years of age reported a history of injection drug use, the strongest risk factor for HCV infection. Of all persons reporting such a history, 83.3% had not used injection drugs for at least 1 year before the survey. Other significant risk factors included 20 or more lifetime sex partners and blood transfusion before 1992. Abnormal serum ALT levels were found in 58.7% of HCV RNA-positive persons. Three characteristics (abnormal serum ALT level, any history of injection drug use, and history of blood transfusion before 1992) identified 85.1% of HCV RNA-positive participants between 20 and 59 years of age. Limitations: Incarcerated and homeless persons were not included in the survey. Conclusions: Many Americans are infected with HCV. Most were born between 1945 and 1964 and can be identified with current screening criteria. History of injection drug use is the strongest risk factor for infection.

Background: Serologic data on diseases that are preventable by vaccine are useful to evaluate the success of immunization programs and to identify susceptible subgroups. Objective: To provide national estimates of immunity to diphtheria and tetanus by measurement of serum antibody levels. Design: Examination of data from the Third National Health and Nutrition Examination Survey, a representative cross-sectional sample of the U.S. population. Setting: 89 randomly selected locations throughout the United States. Participants: 18 045 persons 6 years of age of older who were examined from 1988 to 1994. Measurements: Serum samples obtained at a single time point were tested for diphtheria and tetanus antitoxin. Results: Overall, 60.5% of Americans 6 years of age or older had fully protective levels of diphtheria antibody (>=0.10 IU/mL) and 72.3% had protective levels of tetanus antibody (>0.15 IU/mL). Ninety-one percent of Americans 6 to 11 years of age had protective levels of both diphtheria and tetanus antibody; this proportion decreased to approximately 30% among persons 70 years of age (29.5% for diphtheria and 31.0% for tetanus). Adult Mexican-Americans were slightly less likely to have protective levels of antibody to both toxins. Only 47% of persons 20 years of age or older had levels that were protective against both diseases, and only 63% of adults who were protected against tetanus were also protected against diphtheria. Conclusions: A substantial proportion of adults in the United States do not have antibody levels that are protective against diphtheria and tetanus. In addition, although the recommended vaccine is a combination of tetanus and diphtheria, only 63% of adults with protective antibody to tetanus also had protective antibody to diphtheria.