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Notes from the Field: Investigation of Leptospirosis Underreporting — Puerto Rico, 2010

Leptospirosis, a zoonosis transmitted through contact with the urine of infected animals, either directly or through exposure to contaminated water or soil, is a frequent cause of acute febrile illness (AFI) (1) and can be difficult to distinguish from dengue in areas where both are endemic (2,3). Approximately 5%–10% of patients with leptospirosis are affected severely; the case-fatality rate in those with severe disease is 5%–15% (4). Early identification of leptospirosis cases and early administration of penicillin G or doxycycline can reduce the duration and severity of illness (5).

Human leptospirosis is a reportable disease in Puerto Rico. During 2000–2009, approximately 15–100 cases of suspected leptospirosis were reported to the Puerto Rico Department of Health (PRDH) each year. In 2010, a total of 59 leptospirosis cases were reported, including one death. Barriers to determining the actual burden of leptospirosis in Puerto Rico include the unavailability of diagnostic testing on the island, no system of veterinary surveillance to detect animal cases, and no environmental surveillance to identify circulating serovars.

In January 2010, CDC's Dengue Branch initiated enhanced surveillance in Puerto Rico to determine the rate of dengue deaths through detection of fatal AFI cases at hospitals and pathology laboratories, and through review of death certificates. Autopsy tissue specimens from suspected cases were tested by CDC's Infectious Diseases Pathology Branch for dengue virus and other pathogens, including Leptospira (the cause of leptospirosis).

This enhanced fatal AFI surveillance system identified 20 laboratory-confirmed and five suspected fatal cases of leptospirosis in 2010 in Puerto Rico (0.67 deaths per 100,000 residents). If the PRDH passive case reporting system captured all cases of leptospirosis, three to nine reported deaths from 59 reported cases would have been expected, for a rate of 0.08–0.24 deaths per 100,000. These findings suggest that 60%–90% of fatal leptospirosis cases are not reported, reflecting underrecognition of cases, underreporting, or both.

As a first step toward developing strategies to improve leptospirosis surveillance and diagnostic capacity in Puerto Rico, reasons for underreporting were investigated. A convenience sample of 19 physicians and 39 veterinarians were interviewed to assess their knowledge of the clinical presentation and treatment of leptospirosis and reporting requirements. The physician interviewees were volunteers from two academic medical centers in Puerto Rico, and the veterinarians who were interviewed were recruited during a major veterinary conference. The physicians and veterinarians also were asked about their perception of barriers to reporting cases of leptospirosis and barriers to leptospirosis diagnostic testing. Of those interviewed, 95% were able to describe the signs and symptoms, risk factors, and appropriate treatment for leptospirosis. All believed diagnostic services were not timely, and very few were satisfied with the availability. More than 95% of physicians also believed they could distinguish leptospirosis from dengue. All veterinarian interviewees were willing to report cases of leptospirosis in animals if a case reporting system was in place.

Lack of timely diagnostic services and the absence of a system to report animal cases of leptospirosis (which could act as sentinels for risk of human disease) appear to be barriers to reporting cases in humans and animals, respectively. To strengthen leptospirosis surveillance, prevention, and diagnostic services, PRDH and CDC agreed on a plan to 1) implement a new surveillance system that records suspected cases of leptospirosis in humans and animals; 2) develop diagnostic capacity for leptospirosis within PRDH or clinical laboratories; 3) promote use of Food and Drug Administration–approved rapid tests in the field; and 4) revise case definitions for reporting. The new system will integrate case report data with laboratory data from PRDH, which will confirm cases and identify serovars.

Reported by

Brenda Rivera, DVM, Puerto Rico Dept of Health. William A. Bower, MD, Marta Guerra, DVM, Dianna Blau, DVM, Div of High-Consequence Pathogens and Pathology, Kay M. Tomashek, MD, Div of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases; Mahesh Swaminathan, MD, Tyler Sharp, PhD, EIS officers, CDC. Corresponding contributor: Marta Guerra,, 404-639-3951.


  1. McBride AJ, Athanazio DA, Reis MG, Ko AI. Leptospirosis. Curr Opin Infect Dis 2005;18:376–86.
  2. Bruce MG, Sanders EJ, Leake JA , et al. Leptospirosis among patients presenting with dengue-like illness in Puerto Rico. Acta Trop 2005;96:36–46.
  3. Libraty DH, Myint KSA, Murray CK, et al. A comparative study of leptospirosis and dengue in Thai children. PLoS Negl Trop Dis 2007;1:e111.
  4. Levett PN. Leptospirosis. Clin Microbiol Rev 2001;14:296–326.
  5. Edwards CN, Nicholson GD, Hassell TA, Everard CO, Callender J. Penicillin therapy in icteric leptospirosis. Am J Trop Med Hyg 1988;39:388–90.

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