Leptospirosis-Associated Hospitalizations, United States, 1998–2009 - Volume 20, Number 8—August 2014 - Emerging Infectious Disease journal - CDC
Volume 20, Number 8—August 2014
Leptospirosis-Associated Hospitalizations, United States, 1998–2009
Leptospirosis is a bacterial zoonotic infection caused by pathogenic serovars in the genus Leptospira (1). Approximately 10% of infections in humans result in clinical disease characterized by abrupt onset of fever, headache, muscle aches, and gastrointestinal involvement (2,3). Some infected persons can experience biphasic illness, in which more severe symptoms begin after a short recovery period (2,3). A total of 10%–15% of patients with clinical disease experience severe leptospirosis, characterized by multiple organ involvement (e.g., renal and liver failure, pulmonary distress and hemorrhage, cardiac arrhythmia), and a high rate of death (2,3). Severe infections comprise the majority of reported cases, but these cases underrepresent the incidence of disease (4).
Leptospirosis has historically occurred in persons who have contact with fresh water following heavy rains and in persons who work outdoors, with animals, or in wet environments contaminated with animal urine (2,3,5). The disease occurs more frequently in adult men than in children or women (4,6), and it is most prominent during warm and rainy seasons (2,3). In the United States, new groups at risk for leptospirosis have emerged, including residents in urban areas (7) and participants in freshwater sports (8,9).
In most places worldwide, leptospirosis is considered a reemerging human and animal disease (1,5). However, the disease was not considered nationally notifiable during 1995–2012, so whether human leptospirosis is reemerging in the United States is unknown (10). During those years, leptospirosis was reportable in many states; among them, California and Hawaii showed reemergence of the disease (11,12). In addition, a report describing a higher than expected death rate among leptospirosis-infected persons in Puerto Rico suggested that, on the basis of the average death rate, many more clinical cases of leptospirosis should have been reported (13). The fewer than expected number of reported cases might have resulted from underreporting or from a lack of disease recognition. The findings in those reports indicate the potential reemergence of leptospirosis as a public health problem in the United States.
To increase our knowledge of this neglected disease in the United States, we used national hospital discharge data for 1998–2009 to estimate the number of persons in the US population with symptomatic leptospirosis requiring hospitalization. We also used the discharge data to evaluate trends of leptospirosis-associated hospitalizations during the study period and to compare hospitalizations for leptospirosis with those for other infectious diseases.