The emergence of another tickborne infection in the 12-town area around Lyme, Connecticut: Human granulocytic ehrlichiosis

Human granulocytic ehrlichiosis (HGE) is an emerging tickborne infection, i ncreasingly recognized in areas in which Lyme disease is endemic, but there are few data on the incidence of HGE. Prospective population-based surveil lance was conducted in the 12-town area around Lyme, Connecticut, by means of both active and passive methods, from April through November of 1997, 19 98, and 1999. Five hundred thirty-seven residents presenting to their prima ry care provider with an acute febrile illness suggestive of HGE were ident ified. Of these, 137 (26%) had laboratory evidence (bg indirect fluorescent antibody staining or polymerase chain reaction) of HGE; 89 were confirmed cases, and 48 were probable cases. The incidence of confirmed HGE was 31 ca ses/100,000 in 1997, 51 cases/100,000 in 1998, and 24 cases/ 100,000 in 199 9. A subset of sera was tested by use of immunoblot assays, and results wer e in agreement with indirect fluorescent antibody methods for 86% of sample s analyzed. Thus, HGE is an important cause of morbidity and is now the sec ond most common tickborne infection in southeastern Connecticut.