Leptospirosis in travellers

International travel is growing rapidly worldwide. It has been estimated that international travellers will reach nearly 1.6 billion by 2020, with the highest rise in tropical and subtropical areas [1]. Leptospirosis is considered the most widespread zoonosis, occurring worldwide except in polar regions. During the past decade, leptospirosis has been increasingly recognized among adventure travellers in temperate and tropical areas. Protean manifestations of leptospirosis and unawareness of this illness as a cause of fever in the returning traveller may lead to many unrecognized cases [2,3]. Because the outcome of the disease is potentially fatal, physicians should consider leptospirosis in febrile travellers with compatible epidemiological history, and promptly administer treatment.

Transmission of leptospirosis may occur worldwide in both rural and urban areas; however, the incidence of infection is significantly higher in tropical areas [4,5,8–12]. Traditionally, leptospirosis has been considered an occupational hazard among professionals in contact with urine of infected animals [9,13]. However, outbreaks are increasingly reported among adventure travellers and athletes participating in freshwater sports [10,11,14–20]. Information regarding prophylactic measures should be targeted at this group of travellers and leptospirosis should be considered in febrile travellers returning with a compatible epidemiologic association [7,9,21].

The precise incidence of leptospirosis remains unknown because of the worldwide lack of awareness or systemic investigation for this illness. Estimates of annual incidence rates range from 0.02 to 1/100,000 persons in temperate areas and from 10 to 100/100,000 persons in humid tropics. During outbreaks, and in high-risk exposure groups, incidence may reach 100/100,000 persons [6,22]. Climate and rainfall influence the incidence and seasonality of leptospirosis. The higher incidence in the tropics is related to the longer survival of leptospires in the warm and humid environment, and in tropical areas to the presence of stagnant waters and poor sanitary conditions [22]. Although an increasing number of imported leptospirosis cases and outbreaks following international travel and adventure activities has been published during the last decade [5,10,11,15,17,20,24–26], most leptospiral infections in this group probably remain unrecognized. Reasons for this include the non-specific symptoms commonly encountered in leptospirosis, the lack of awareness of this illness as a cause of fever among returning travellers, and the relative unavailability of testing. However, given the increasing popularity of travel and eco-tourism in tropical areas, it appears that the risk and thus the incidence of leptospirosis among travellers will increase. Examples of leptospirosis outbreaks include the outbreak in Springfield, Illinois in 1998, at an international triathlon athletic event, where the attack rate was 12% among 834 participants [11], and the outbreak that occurred among 304 athletes from 27 countries in the ‘Eco-Challenge’ multisport race in Malaysia in 2000 with an attack rate of 62% of all athletes [10].

Adventure travellers, athletes participating in freshwater sports, and military recruits travelling in areas endemic for leptospirosis should be informed about the risk of infection during high-risk activities and advised about preventive measures: wearing protective waterproof clothes and boots, avoiding submersion and consumption of river water, and covering cuts and abrasions with waterproof dressings in order to minimize exposure to a contaminated environment. Special attention should be paid to travellers travelling to areas recently affected by floods. Drinking water should be purified by boiling and treating with chlorine. Filtration of water might not be effective because of the size of the organism which can pass through 0.45 µM filters [9].

Pre-travel counselling should focus on preventive measures, including the administration of prophylactic doxycycline for travellers engaged in freshwater activities in endemic areas. Pre-exposure doxycycline chemoprophylaxis at 200 mg/week p.o. should be considered for high-risk travellers. High-risk activities include fresh water swimming, rafting, kayaking, canoeing, fishing, hunting, and trail biking. Health-care providers should be aware of the possibility of imported leptospirosis among febrile returning travellers with a compatible epidemiological history, and administer appropriate treatment.

References
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Androula Pavli, Travel Medicine Office

Helena Maltezou, Department for Interventions in Health-Care Facilities

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