THE IMPORTANCE OF LEPTOSPIROSIS IN SOUTHEAST ASIA KANTI LARAS, CAO BAO VAN, KHANTHONG BOUNLU, NGUYEN THI KIM TIEN, JAMES G. OLSON, SISOUK THONGCHANH, TRAN NGUYEN VAN ANH, HOANG KIM LOAN, NARAIN PUNJABI, HA BA KHIEM, UNG SAM AN, SITHAT INSISIENGMAY, DOUGLAS M. WATTS, H. JAMES BEECHAM, AND ANDREW L. CORWIN U.S. Naval Medical Research Unit No. 2 (US NAMRU-2), Jakarta, Indonesia; Pasteur Institute, Ho Chi Minh City, Socialist Republic of Vietnam; Center of National Laboratory and Epidemiology, Vientiane, Lao PDR; U.S. NAMRU-2/NIPH, Phnom Penh, Cambodia; National Institute of Public Health, Phnom Penh, Cambodia; U.S. Naval Medical Research Center, SilverSpring,Maryland. Abstract. The importance of leptospirosis in Southeast Asia was assessed in conjunction with other studies supported by the U.S. Naval Medical Research Unit No. 2 (US NAMRU-2), Jakarta, Republic of Indonesia. These included studies of hospital-based, acute clinical jaundice in Indonesia, Lao PDR, and Socialist Republic of Vietnam; nonmalarial fever in Indonesia; and hemorrhagic fever in Cambodia. Background prevalence estimates of leptospiral infection were obtained by a cross-sectional, community-based study in Lao PDR. Laboratory testing methods involved serology, microscopic agglutination test, and reverse-transcriptase polymerase chain reaction. Suggestive evidence of recent leptospiral infections was detected in 17%, 13%, and 3% of patients selected on the basis of non–hepatitis A through E jaundice, nonmalarial fever, and hemorrhagic fever (in the absence of acute, dengue viral infections). Leptospiral IgG antibody, reflective of prior infections, was detected in 37% of human sera, collected in Lao PDR. The predominant leptospiral serogroups identified from cases with clinical jaundice were Hurstbridge, Bataviae, and Icterohaemorrhagiae tonkini LT 96 69. Among the nonmalarial febrile cases, Bataviae was the most frequently recognized serogroup. Pyrogenes and Hurstbridge were the principal serogroups among the hemorrhagic fever case subjects. These findings further attest to the relative importance of clinical leptospirosis in Southeast Asia. The wide spectrum of clinical signs and symptoms associated with probable, acute, leptospiral infections contributes to the potential of significant under- reporting. INTRODUCTION Leptospirosis is caused by bacteria from the genus Lep- tospira, which comprises 12 species (L.alexanderi,L.biflexa, L. borgpetersenii, L. fainei, L. inadai, L. interrogans, L. kir- schneri,L.noguchii,L.santarosai,L.weilii,L.meyeri, and L. wolbachii). To date, only L. interrogans and L. fainei have been reported as pathogenic in humans. 1,2 Common symp- toms of leptospirosis in humans are sudden onset of fever, headache, chills, severe myalgia, and conjunctival suffusion. 3 Southeast Asia is an endemic area for leptospirosis, and infection in humans has been reported throughout the re- gion. 4–10 Of the serovars included in the major pathogenic species, 70% have been isolated in Asia 4 . The nonspecificity of signs and symptoms and the limited availability of labora- tory confirmation in endemic areas probably have contrib- uted to significant underreporting, however, most notably in association with jaundiced disease. 7 High regional endemicity of other diseases, such as malaria and dengue hemorrhagic fever, also leads clinicians to assign presumptive diagnostic status in the absence of supportive laboratory testing and alternative diagnostic considerations (e.g., leptospirosis). The purpose of this study was 4-fold: (1) to measures the relative importance of leptospiral infection in association with various clinical presentations; (2) to measure the relative im- portance of leptospiral infections in conjunction with jaundice case criteria from diverse localities in Southeast Asia; (3) to recognize possible clustering of leptospiral serogroups, as a function of specific clinical presentations (signs and symp- toms); and (4) to determine background endemicity of lep- tospirosis (in Lao PDR). METHODS Investigation of leptospirosis was sponsored by the U.S. Naval Medical Research Unit No. 2 (US NAMRU-2) Jakarta (Indonesia), in collaboration with partner institutions throughout Southeast Asia. This investigation was carried out in conjunction with the following related studies: (1) a study of causes of acute, hospital-recognized jaundice disease (con- ducted in Lao PDR, Socialist Republic of Vietnam, and Indonesia); (2) a study of causes of nonmalarial febrile disease (conducted in Irian Jaya, Indonesia); (3) a study of causes of hemorrhagic fever disease (conducted in Cambo- dia); and (4) a cross-sectional, community-based study of background Leptospira infection (conducted in Lao PDR) (Figure 1, Table 1). All studies, hospital-based (clinical) and community-based (nonclinical), were carried out in the pe- riod 1993–2001. Sera collected during acute jaundice disease studies were tested for hepatitis A, B, C, and E virus markers by enzyme- linked immunosorbent assay (ELISA) (Abbott Laboratories, Abbott Park, IL) at U.S. NAMRU 2, Jakarta. Sera negative for hepatitis A–E viruses were tested at the Pasteur Institute in Ho Chi Minh (HCM) City for evidence of recent leptospi- ral infections by microscopic agglutination test (MAT) 11 and polymerase chain reaction (PCR). 12,13 Sera collected from clinical patients with nonmalarial fever and nondengue hemorrhagic febrile manifestations first were screened by PanBio Leptospira IgM ELISA kit (Panbio Ltd, Brisbane, Australia) at the National Institutes of Public Health (NIPH)/U.S. NAMRU-2 laboratory, Phnom Penh, Cambodia. Positive ELISA specimens were tested by MAT and PCR at Pasteur Institute, HCM City. Before testing for recent evidence of leptospiral infections, all sera collected during the nonmalarial febrile study were examined for ma- laria parasitemia by microscopy at U.S. NAMRU-2, and sera from the hemorrhagic fever disease study were tested for den- gue antibody using IgM capture ELISA reagents supplied by the U.S. Armed Forces Research Institute of Medical Sci- ences (U.S. AFRIMS), Bangkok, Thailand. Am. J. Trop. Med. Hyg., 67(3), 2002, pp. 278–286 Copyright © 2002 by The American Society of Tropical Medicine and Hygiene 278