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Journal of Clinical Microbiology, 10, 852-853. Received 28 April 2000; revised 8 August 2000; acceptedfor publication 8 August 2000 TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE (2001) 95,137-138 A double-blind randomized therapeutic trial of insect repellents for the prevention of malaria in pregnancy R. McGready1*2y3, J. A. Simpson2*3, M. Htway’ , N. J.White*,‘, F. Nosten’*233 and S. W. Lindsay4 ‘Shoklo Malaria Research Unit, I? 0. Box 46, Mae Sot 63110, Thailand; ’ Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand; 3Centre for Tropical Med- icine, Nujtield Department of Medicine, John RadclaIe Hospital, Headington, Oxford, UK; ‘Department of Bio- logical Sciences, University of Durham, Durham DH13LE, UK, and Danish Bilharziasis Laborato y, Charlottenlund, Denmark Keywords: malaria, Plasmodium falciparum, Plasmodium vivax, pregnancy, diseaseprevention, repellents, DET, Thailand The spread of multidrug-resistant malaria is threaten- ing malaria control in pregnancy on the western border of Thailand because of the paucity of effective preventive measures (DOLAN et al., 1993) and lack of treatment options (MCGREADY et al., 1998) against the highly drug-resistant Plasmodium falciparum parasites prevalent in this region. The aim of this randomized, blinded intervention trial was to compare the antimalarial effi- cacy of 20% DET (di-methyl-benzamide) and thanaka (a popular local cosmetic) with thanaka alone, as mos- quito repellent, in pregnant women. The study was carried out in camps for displaced people of the Karen ethnic minority. The effects of malaria in pregnancy (NOSTEN et al., 199 l), the epidemiology of the disease (LUXEMBURGER et al., 1996) and a pilot study of repellent use in this population (LINDSAY et al., 1998), have been described previously. The study received ethical approval from the committees of the Faculty of Tropical Medicine of Mahidol University, the Central Scientific Ethical Committee of Denmark, and the Karen Refugee Committee. Women who were 3-7- months pregnant and gave fully informed consent were provided with full obstetric, medical and delivery care. Weekly malaria smears and 2-weekly haematocrit exam- inations were performed to assess repellent efficacy. The newborn and placenta were weighed with a Salter scale (Model 810) and all newborns were assessed for gesta- tional age with the Dubowitz examination (DUBOWITZ & DUBOWITZ, 1977). Women applied the repellent to their arms and legs every evening at 17:OO. Daily compliance was self-reported weekly and actively reported monthly by random home visits. Between April 1995 and September 1996, 897 preg- nant women were enrolled in the study, 449 into the DET and thanaka group and 448 into the thanaka alone group with no difference in baseline characteristics. Delivery while using repellent was reported for 681 (75.9%) women, while 149 (16.6%) women moved or were lost before completion of the study, 51 (5.7%) women stopped because of adverse reactions, 15 (1.7%) women had abortions, and 1 woman died (0.1%) of hypertension at 7-months gestation. Women were fol- lowed for a median period of 18 weeks (range O-32 weeks) and no differences in duration of follow-up or birth outcomes were found in the 2 treatment groups (Table). Overall there were 115 patent parasitaemic episodes of I? falciparum (including 10 mixed infections) detected in 9 1 of the 897 women during the study (9 l/897,10* 1%). There was a 28% reduction in the incidence of falcipar- urn malaria for women using DET and thanaka, 10.6% (95% confidence interval 7.5, 13.7), compared to wo- men using thanaka alone, 14.8% (9.9,19.7), but this did not reach statistical significance (log rank test, P = 0.26). I? vivax incidence also showed a non-significant reduc- tion (9%), DET and thanaka 21.1% (16.6, 25.6) vs thanaka alone 26.4% (21.1, 31.7); log rank test, P= 0.51. There was no significant difference between the incidence of anaemia (excludes women who were anae- mic on admission) in the 2 groups, DET and thanaka 55% (1611293) vs thanaka alone 52% (153/294); P= 0.53. Women who were parasitaemic during the study were more likely to be anaemic on admission than women who had no documented malaria, 42.7% vs 30.6%, P= 0.001, indicating they may already have been infected before entering the study. Compliance with the daily use ofrepellents was self-reported at 90.5% (87 7 15196 955) for evening use, and actively detected at 84.6% (191812267) on random home visitor checks, with no difference between the groups; P = 0.24. Transmission was in fact too low to give any confident Address for correspondence: Dr F. Nosten, Shoklo Malaria Research Unit, P.O. Box 46, Mae Sot, Tak 63110, Thailand; e-mail shoklo@cscoms.com