DENGUE Leptospirosis during Dengue Outbreak, Bangladesh Regina C. LaRocque,* Robert F. Breiman,† Mary D. Ari,‡ Roger E. Morey,‡ Firdous Ara Janan,§ John Mosely Hayes,¶ M. Anowar Hossain,† W. Abdullah Brooks,† and Paul N. Levett‡ We collected acute-phase serum samples from febrile patients at 2 major hospitals in Dhaka, Bangladesh, during an outbreak of dengue fever in 2001. A total of 18% of dengue-negative patients tested positive for leptospirosis. The case-fatality rate among leptospirosis patients (5%) was higher than among dengue fever patients (1.2%). Lchetes of the genus Leptospira. Infection usually eptospirosis is a zoonotic infection caused by spiro- results when water or soil contaminated with the urine of an infected animal comes in contact with human skin or mucous membranes (1). Clinical manifestations of lep- tospirosis can range from a self-limited febrile syndrome to a fatal illness (Weil disease) characterized by hemor- rhage, renal failure, and jaundice. In tropical settings, lep- tospirosis can be indistinguishable from other febrile illnesses such as scrub typhus, malaria, or dengue. Although leptospirosis has been reported in neighbor- ing areas of Southeast Asia (2,3), the disease is not recog- nized in Bangladesh, where diagnostic tests for leptospirosis are not available. However, environmental factors, such as floods, humidity, and water contamination, are amenable to spread of the disease in Bangladesh. An epidemic of dengue fever and dengue hemorrhagic fever began in Bangladesh in 2000 (4), and a surveillance system was established to identify patients with dengue- like illness at 2 major hospitals in Dhaka. Approximately three-quarters of patients meeting surveillance criteria had laboratory evidence of dengue infection. We hypothesized that leptospirosis might be a cause of illness among febrile patients who did not have dengue fever. To assess this, we retrospectively analyzed acute-phase serum samples from *Massachusetts General Hospital, Boston, Massachusetts, USA; †International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh; ‡Centers for Disease Control and Prevention, Atlanta, Georgia, USA; §Dhaka Medical College Hospital, Dhaka, Bangladesh; and ¶Centers for Disease Control and Prevention, San Juan, Puerto Rico, USA DISPATCHES all dengue-negative patients by using real-time polymerase chain reaction (PCR) for Leptospira. We used data collect- ed as part of the surveillance program to identify distin- guishing clinical characteristics of leptospirosis. The Study In 2000, the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B) worked with staff from Dhaka Medical College and Holy Family Red Crescent Hospital to initiate surveillance for dengue as part of an emergency response to an epidemic of dengue and dengue hemorrhagic fever. Physicians at Dhaka Medical College and Holy Family Red Crescent Hospital were trained in the clinical diagnosis and management of dengue and dengue hemorrhagic fever according to World Health Organization guidelines. Patients hospitalized with fever and in whom a physician suspected dengue were enrolled in the surveillance program. Clinical and epidemiologic information, as well as acute-phase serum specimens, were systematically collected from surveillance patients. Acute- phase serum specimens were assessed for dengue virus antibodies by using a commercial immunoglobulin (Ig)G and IgM capture enzyme-linked immunosorbent assay (ELISA) (PanBio Dengue Duo, PanBio Ltd., Brisbane, Queensland, Australia) (5). In addition, serum samples col- lected from a subset of patients during the first 5 days of illness were evaluated for dengue virus RNA by using reverse transcriptase–polymerase chain reaction (RT- PCR), as described previously (6). Serum samples from patients with no dengue infection shown by antibody or RT-PCR testing were retrospectively assessed for lep- tospirosis by using a real-time PCR that amplifies the LipL32 gene (7), a virulence factor that is conserved among pathogenic Leptospira strains (8). Microplate Leptospira IgM ELISA testing (PanBio Ltd) was conduct- ed on all Leptospira PCR-positive serum specimens of suf- ficient quantity (9). Specimens from 1,297 patients hospitalized at Dhaka Medical College and Holy Family Red Crescent Hospital between January 1 and December 31, 2001, were evaluat- ed for dengue infection by using capture ELISA; 55 acute- phase serum samples were additionally evaluated by using RT-PCR for dengue. A total of 938 (72%) patients were diagnosed with dengue fever by serology (932 patients), RT-PCR (3 patients), or both (3 patients). Acute-phase serum specimens from the 359 patients without laboratory evidence of dengue were evaluated for leptospirosis; 63 (18%) had Leptospira detected by using PCR. Sixty-one of the PCR-positive samples were tested for Leptospira-spe- cific IgM; 18 (30%) showed positive results and 5 (8%) showed equivocal results. Patients with leptospirosis diagnosed by using PCR were 6 to 70 years of age (mean 28, SD 13); 74% were 766 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 11, No. 5, May 2005