75 ORI GI NAL ARTI CLE ABSTRACT Aim: to investigate which recent infection could have caused the present dengue-like symptoms, in adult patients clinically fulfilling the WHO criteria for dengue, in which serologically were not confirmed for dengue virus infections. Methods: prospective study. During an outbreak of dengue (between May 1995 and May 1996) 118 consecutive adults ( >13 years) suspected by the WHO 1997 case definition of DF or DHF were investigated. Patients were examined for history of illness, physical and laboratory findings consisting of full blood counts, prothrombin time (PT), activated partial thromboplastin time (aPTT), liver function (bilirubin, ASAT, ALAT), renal function (creatinine), and serological assays included dengue, hantavirus, chikungunya, R. typhi, R. tsutsugamuchi, rubella virus, influenza A virus, and leptospira. Results: in 58 of the total 118 patients, recent dengue virus infection was serologically confirmed. In 20 of the remaining 60 patients, we found serological evidence of another recent infection: hantavirus (5), chikungunya virus (2), R. typhi (5), R. tsutsugamuchi (2), rubella virus (3), influenza A virus (1), and leptospira (2). No evidence for recent infection with any of the mentioned agents was detected in the remaining 40 specimens. Conclusion: we conclude that based on clinical characteristics alone, it is not easy to diagnose dengue. Specific laboratory tests to differentiate dengue from other febrile illnesses are needed. Among these, in Indonesia hantavirus infection should be considered as well. Key words: hantavirus, dengue virus infection, rickettsia, chikungunya. Hanta Virus Infection During Dengue Virus Infection Outbreak in Indonesia Catharina Suharti*, Eric C.M. van Gorp**, Wil M.V. Dolmans***, Jan Groen****, Suharyo Hadisaputro*, Robert J. Djokomoeljanto*, Osterhaus Ab D.M.E.****, Jos W.M. van der Meer*** * Department of Internal Medicine, Faculty of Medicine, Diponegoro University-Dr. Kariadi Hospital. Jl. Dr. Soetomo no. 18, Semarang, Indonesia, ** Department of Internal Medicine, Slotervaart Hospital, Amsterdam, *** Department of Medicine, University Medical Centre St Radboud, Nijmegen, The Netherlands, **** Institute of Virology, Erasmus University Hospital, Rotterdam, The Netherlands. Correspondence mail to: catrin@indosat.net.id. INTRODUCTION Indonesia has a tropical climate and humidity which is conducive to perpetuation of Aedes aegypti, the main vector of dengue. Dengue virus belongs to the genus Flavivirus, family Flaviviridae and may cause a wide spectrum of illness: asymptomatic infection, dengue fever (DF) and dengue hemorrhagic fever (DHF). 1 Clinical signs and symptoms of dengue fever are not specific and include sudden onset of fever, weakness, headache, joint pain, muscle pain, retro-orbital pain, nausea, vomiting, and rash. The less severe grades of DHF (grade I and II) manifest similar to DF with signs of spontaneous bleeding, and are difficult to distinguish from other viral illnesses found in tropical areas such as chikungunya virus infection (which is also transmitted by Ae. Aegypti), influenza, mild hantavirus infection and rubella, as well as bacterial infections such as mild leptospirosis and rickettsiosis. 1-7 Epidemiological studies have demonstrated that during outbreaks of dengue 10.5% to 42.7% of cases can be detected by virus isolation, 8,9 46.3% by IgM/IgG ELISA, 9 41.8% by hemagglutination inhibition (HI) tests, 10 41.4 to 66% by IgM ELISA and/or virus isolation, 11,12 and 73% by HI and/or virus isolation. 13 Thus, the rest of these patients may actually suffer from another febrile illnesses. Alternatively, the sensitivity of tests used may have been low, or a wrong sampling time-point for the test was used. We studied a group of patients >13 years clinically suspected of recent dengue virus infection, of whom some were confirmed serologically but others not. We asked the question which other infectious agents could