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BACKGROUND: Leptospirosis is a zoonotic disease caused by bacteria of the genus Leptospira spp. It is considered to be the most widespread zoonotic disease, and is most commonly found in tropical or temperate climates. Traditionally, leptospirosis cases have been associated with occupational exposures through close contact with animals. However, recent trends suggest emergence of recreational and avocational risk groups. Leptospirosis is a reportable disease in more than 30 U.S. jurisdictions, and was one of 69 notifiable infectious conditions listed by the National Notifiable Diseases Surveillance System (NNDSS) in 2014.
METHODS: Leptospirosis cases in 2013 and 2014 were identified through three data sources: 1) requests to CDC for diagnostic assistance or interpretation from physicians and health departments; 2) specimen submissions to CDC’s Zoonoses and Select Agent Laboratory (ZSAL) for identification or confirmation; and 3) NNDSS.
RESULTS: CDC conducted specimen testing for 118 individuals in 2013-14, out of which 44 (37%) tested positive for leptospirosis; 11 (25%) had presumptive results for acute leptospirosis and 33 (75%) had confirmatory results based on PCR, serology, and culture. A review of leptospirosis case notifications through NNDSS from 2013-14 revealed 139 reported cases. Seventy-four (53%) were confirmed, while 61 (44%) met criteria for probable case classification. Two cases were identified as suspect, and two listed as unknown classification. Cases were distributed across 13 jurisdictions within the continental U.S.; however largest case burdens were reported from Puerto Rico (68%) and Hawaii (14%). The average age of those infected was 42, with 18 (13%) pediatric cases. In the two years of study, CDC received case report forms for nine cases of leptospirosis. Cited sources of exposure were recreational swimming in freshwater, occupational exposure to rodents in urban environments, occupational contact with a potentially contaminated watershed, and close contact with pet dogs.
CONCLUSIONS: Several factors, such as recent relisting as a notifiable condition, limited variables received through NNDSS, and limited exchange of case report forms, have likely resulted in underreporting of leptospirosis in the United States and minimal risk factor information. In order to estimate the true burden of disease and better characterize at-risk populations, CDC encourages state health departments to share information that can lead to prevention and care for leptospirosis. Interaction between clinicians, states and CDC can help improve surveillance, data-sharing, prevention programs, and diagnostic methods for leptospirosis detection.