Seroprevalence to Bartonella quintana among patients at a community clinic in downtown Seattle.

In 1993, an outbreak of 10 cases of Bartonella quintana bacteremia occurred among homeless, alcoholic, human immunodeficiency virus (HIV)-negative persons in Seattle. To estimate the prevalence of past exposure B. quintana among this population, a serosurvey was conducted in 1994 among patients at a downtown Seattle clinic. Microimmunofluorescent titers to B. quintana in 192 clinic patients were compared with titers in 199 age- and sex-matched Seattle volunteer blood donors. Titers > or = 64 were detected in 20% (39/192) of clinic patients compared with 2% (4/199) of blood donors (P<.001). Among clinic patients, alcohol abuse was independently associated in multivariate analysis with titers > or = 64 (odds ratio, 3.3; 95% confidence interval, 1.6-6.9). Of the 39 patients with B. quintana titers > or = 64, 24 (62%) also had titers > or = 64 to Bartonella henselae, indicating serologic cross-reactivity between Bartonella species. These results suggest that a substantial proportion of this indigent, inner-city Seattle population was infected with B. quintana.