PREDICTIVE FACTORS OF RICKETTSIOSES Vol 35 No. 3 September 2004 657 Correspondence: Dr Chansuda Wongsrichanalai, US Naval Medical Research Unit No. 2 (NAMRU-2), Kompleks P2M/PLP-LITBANGKES, Jalan Percetakan Negara No. 29, Jakarta 10560, Republic of Indonesia. Tel: 62-21-421-4457; Fax: 62-21-420-7854 E-mail: chansuda@namru2.med.navy.mil The opinions or assertions contained herein are those of the authors and should not be construed as reflect- ing the official positions of the US Department of the Army or Department of Defense. INTRODUCTION Rickettsioses are caused by obligate, intra- cellular, gram-negative coccobacilli bacteria in the Order Rickettsiales. For recent taxonomic reclas- sification within the Order Rickettsiales please refer to Dumler et al (2001). Rickettsial infec- tions may vary in their manifestations from mild and self-limiting to severe and fatal. Scrub typhus A STUDY OF FEBRILE ILLNESSES ON THE THAI-MYANMAR BORDER: PREDICTIVE FACTORS OF RICKETTSIOSES Amy L Pickard 1,2 , Philip McDaniel 3 , R Scott Miller 1 , Nichapat Uthaimongkol 1 , Nillawan Buathong 1 , Clinton K Murray 4 , Sam R Telford III 5 , Philippe Parola 1,5,6 and Chansuda Wongsrichanalai 1 1 Armed Forces Research Institute of Medical Sciences (AFRIMS), Bangkok, Thailand; 2 University of North Carolina School of Public Health, Chapel Hill, NC, USA; 3 Kwai River Christian Hospital, Sangkhla Buri, Kanchanaburi, Thailand; 4 Brooke Army Medical Center, Fort Sam Houston, San Antonio, TX, USA; 5 Harvard School of Public Health, Boston, MA, USA; 6 Unité des Rickettsies, WHO Collaborative Center for Rickettsial Reference and Research, Faculty of Medicine, Marseilles, France Abstract. We have performed a case-control analysis to determine the significance of clinical, labo- ratory and epidemiological features as predictive factors of rickettsioses among patients in Sangkhla Buri, Thailand (Thai-Myanmar border). Fifteen serologically-confirmed rickettsiosis patients in- cluding Spotted Fever Group (SFG) rickettsioses, scrub typhus, and murine typhus were classified as ‘cases’; one hundred and sixty-three acutely febrile patients presenting to the same hospital during the same time period, who had no serological evidence of acute rickettsiosis, were classified as ‘con- trols’. Patients’ report of rash/arthropod bite [Odds ratio (OR) 22.90, 95% CI (confidence interval) 6.23, 84.13] and history of jungle trips (OR 5.30, 95% CI 1.69-16.62) were significant risk factors. Elevated ALT (OR 3.04, 95% CI 1.04, 8.88) and depressed platelet count (OR 3.38, 95% CI 1.13, 10.10) were also useful differentiating markers of rickettsioses in this population. Definitive diagno- sis of rickettsioses is difficult without specialized diagnostic capabilities that are rarely available in remote areas such as Sangkhla Buri, where other acute febrile illnesses with similar presentation are commonly found. The relative importance of predictive factors presented here may provide clini- cians with some useful guidance in distinguishing rickettsioses from other acute febrile illnesses. Timely administration of empiric treatment in highly suspicious cases can deter potential morbidity from these arthropod-borne infections. (due to Orientia tsutsugamushi and transmitted by chiggers) and murine typhus (due to Rickett- sia typhi and transmitted by fleas) have long been known as the most common rickettsioses in the Southeast Asian region (Sangkasuwan et al, 1969; 1973; Silpapojakul et al, 1993; Chen et al, 2001; Ong et al, 2001). However, tick- and flea-borne Spotted Fever Group (SFG) rickettsioses are also present (Sirisanthana et al, 1994; Parola et al, 2003b). Infections caused by rickettsiae are of- ten undiagnosed outside of specialized referral centers, but the diseases are treatable. Fatal out- comes may result from misdiagnosis or delayed treatment. Thailand’s Sangkhla Buri district (Kancha- naburi Province), is a malaria endemic area on the Thai-Myanmar border. Patients presenting with acute fever in this region are first screened by ma- laria smear. If found to be malaria negative, spe-