Leptospirosis in Hawaii: 1999-2006: Epidemiologic and clinical analysis of 174 laboratory-confirmed cases

Leptospirosis is a zoonotic illness with worldwide distribution. From the mid 1970s through 1994, when it was dropped from the list of nationally notifiable infectious diseases, Hawaii consistently had the highest reported annual incidence rate in the United States. Cases remain reportable in Hawaii. The last large surveillance report on leptospirosis in the United States emanated from Hawaii and covered the years 1974-1998. The purpose of this study is to assess the current status of leptospirosis in Hawaii. From 1999 through 2006, 297 cases of leptospirosis were reported of which 286 were acquired through exposures within the state. Laboratory-confirmation, defined by either demonstration of at least a four-fold increase in microscopic agglutination test titer between acute and convalescent phase serum specimens, isolation of Leptospira from a clinical specimen, or demonstration of Leptospira in a clinical specimen by immunofluorescence, was obtained for 174 of the 286 cases (61%). The estimated annual incidence rate was 1.80 per 100,000. Confirmed cases were predominately male (91%), with an age range of 3-76 years (median = 37 years). Exposures leading to disease were most often recreational as opposed to occupational or habitational. Clinical manifestations included fever (98%), myalgias (86%), nausea or vomiting (67%), and jaundice (28%). The case fatality rate was 0.6%. Duration of illness ranged from 3-90 days (median = 14 days). The most common infecting serogroups were Icterohemorrhagiae and Australis. Analyses of large case series with laboratory-confirmation help better delineate the clinical and epidemiologic features of this widespread but underrecognized and underreported illness.